Giardiasis in Children and Adults: Clinical Guidelines

List of Abbreviations

ALT - alanine aminotransferase

AST - aspartate aminotransferase

WHO - World Health Organization

EIA – enzyme immunoassay

GGT - gamma-glutamyl transferase

DNA - deoxyribonucleic acid

Biliary dyskinesia

GI – gastrointestinal tract

EIA – enzyme immunoassay

Infectious diseases department / office

Russian Ministry of Health - Ministry of Health of the Russian Federation

ICD-10 - International Statistical Classification of Diseases and Related Health Problems 10th Revision

INN - international nonproprietary name

Complete blood count (CBC)

Urinalysis

OKI – acute intestinal infections

Compulsory medical insurance of citizens

PCR — polymerase chain reaction

Ultrasound — ultrasound examination

Federal Law

Class A immunoglobulins (IgA)

IgM – class M immunoglobulins

IgG – class G immunoglobulins

WHO - World Health Organization

Terms and Definitions

Evidence-based medicine – an approach to medical practice in which decisions about the use of preventive, diagnostic, and therapeutic measures are made based on available evidence of their efficacy and safety, and such evidence is searched for, compared, summarized, and widely disseminated for use in the best interests of patients.

Disease – a disturbance of bodily function, working capacity, and the ability to adapt to changing environmental conditions arising from the impact of pathogenic factors, accompanied by alterations in the body's protective-compensatory and protective-adaptive reactions and mechanisms.

Quality of medical care – a set of characteristics reflecting the timeliness of medical care, the correctness of the choice of prevention, diagnostic, treatment and rehabilitation methods during the provision of medical care, and the degree of achievement of the planned result.

Clinical guidelines – a document based on proven clinical experience, describing the physician's actions regarding the diagnosis, treatment, rehabilitation and prevention of diseases, and helping them make correct clinical decisions.

Level of evidence certainty – reflects the degree of certainty that the found effect of a medical intervention is true.

Grade of recommendation – reflects not only the certainty in the reliability of the intervention's effect, but also the certainty that following the recommendations will bring more benefit than harm in a specific situation.

Instrumental diagnostics – diagnostics performed by examining a patient using various devices, apparatuses and instruments.

Laboratory diagnostics – a set of methods aimed at analyzing the test material using various specialized equipment.

Medical intervention — a set of medical examinations and/or medical manipulations, as well as artificial termination of pregnancy, performed by a medical worker or other employee entitled to carry out medical activities in relation to a patient, affecting their physical or mental state and having a preventive, diagnostic, therapeutic, rehabilitative, or research focus.

1. Brief information on the disease or condition

1.1 Definition of the disease or condition

Giardiasis is an intestinal protozoosis caused in humans by the flagellated protozoan Lamblia intestinalis (synonyms: Giardia lamblia, Giardia duodenalis, Giardia intestinalis), occurring either as latent parasite carriage or in manifest forms with primary involvement of the small intestine [1, 2, 3, 4].

1.2 Etiology and pathogenesis of the disease or condition (group of diseases or conditions)

Giardiae were first discovered by Antoni van Leeuwenhoek in 1681. The morphology of the parasite was described by Dušan Fedorovič Lambl (Czech: Vilém Dušan Lambl) in 1859, who named it Cercomonas intestinalis. In 1882, Johann Kunstler established that giardiae belong to the genus Giardia. Later, Raphaël Blanchard proposed naming the species Lamblia intestinalis in memory of D.F. Lambl, a name that became firmly established in Russian-language medical literature. However, in international medical literature, according to the rules of biological taxonomy, this protozoan belongs to the genus Giardia, and the species names used are Giardia intestinalis, G. duodenalis, or G. lamblia, which are synonyms of Lamblia intestinalis [1, 2].

Giardiae are parasitic protozoa from the order Retortomonadida, which throughout their life cycle exist in two morphological forms: the trophozoite (the active feeding stage of the parasite responsible for colonizing the host intestine) and the cyst (the infective stage of the parasite's development, ensuring temporary survival in unfavorable external environment conditions and transfer to another host) [4, 5, 7, 8].

Trophozoites (vegetative form of Lamblia intestinalis) — large, motile cells 9–21 micrometers long and 5–15 micrometers wide, bilaterally symmetrical and pear-shaped with a pointed (tapered) posterior end. Their surface bears four pairs of posteriorly directed flagella that help the parasite move and participate in digestion. Two symmetrical nuclei with distinct karyosomes create a smiley-face appearance under microscopy, which is clearly visible in stained preparations. A "ventral disc" is located on the ventral surface of the cell, through which the parasite attaches to the epithelium of the intestinal villi in the upper GI tract [1, 2, 4, 5, 7]. The cyst (resting form) is formed from the trophozoite as a result of encystation; it is oval-shaped, measuring 11–14 × 7–10 µm. In a freshly formed cyst, the rudiments of the locomotor apparatus (curved median bodies and linear axonemes) are clearly visible, as well as two nuclei, the number of which doubles in the mature cyst (Fig. 1B and C). Giardia cysts have a dense, double-contoured wall that protects them from adverse external factors, ensuring long-term viability [1, 4, 5, 6, 7].

Among representatives of the genus Giardia, six species are distinguished, differing in morphology and specific host range. The species Lamblia intestinalis = Giardia intestinalis (syn. G. lamblia and G. duodenalis) inhabits the GI tract of humans and a wide range of mammals (cats, dogs, rats, etc.). G. muris has been found in rodents; G. agilis in amphibians; G. psittaci and G. ardeae in birds; G. microti in voles and muskrats; and G. duodenalis in bats [8, 9, 10].

Using molecular genetic methods, 8 main genetic subtypes (genotypes) within the Lamblia intestinalis species complex have been identified: A, B, C, D, E, F, G, H. Human infections involve Giardia genotypes from groups A and B, within which, in turn, intragroup differences are distinguished: AI–AIII and BIII–BIV. Giardiae of different genetic subtypes differ phenotypically in reproduction rate, drug resistance, resistance to gastric juice, timing of excystation and encystation, metabolic processes, etc. Genotypes A (AI and AII) and B are most commonly detected in humans, while other genotypes are found less frequently [9, 10, 11].

Life cycle of Giardia

The parasite's lifecycle begins with infection of the human gastrointestinal tract after the ingestion of a cyst. In the small intestine, under the influence of bile and trypsin in an alkaline environment, excystation occurs [2]. In the proximal small intestine, cysts rapidly transform into trophozoites (one cyst gives rise to two trophozoites), which attach to intestinal epithelial cells via a sucking (adhesive) disc, after which feeding and reproduction by binary fission begin. As food is mixed by peristaltic movements of the intestine, some lamblia detach from the epithelial cells and pass into the lower parts of the intestine. Encystation occurs in the large intestine—the transformation of trophozoites into cysts, which leave the host organism with feces. Cysts are the only form of L. intestinalis capable of surviving outside the human body, ensuring the possibility of infecting new hosts and the survival of the parasite as a species [1, 2, 3, 4, 6].

Pathogenesis

The mechanisms by which lamblia cause diarrhea and intestinal malabsorption are multifactorial [1, 2, 12]. The habitat of lamblia in the human body is the duodenum and the proximal jejunum, where the most intensive membrane digestion, necessary for the vital activity of these parasites, takes place. Compared to adults, the child's body is most vulnerable to lamblia parasitism because children have the most active membrane digestion processes [1, 2, 3].

The main source of energy for the parasite is glucose; they practically do not utilize other carbohydrates. An excessive carbohydrate content in the diet stimulates the growth of lamblia populations. Low concentrations of bile stimulate the development and reproduction of lamblia, while high concentrations have a detrimental effect on them [7]. Lamblia lack the ability to synthesize most amino acids, and their vital activity depends on the presence of amino acids in the intestinal environment. To generate energy, they actively utilize alanine, arginine, and aspartate [4, 7, 10, 12]. Parasitism of lamblia on the brush border of enterocytes in the duodenum and proximal jejunum disrupts the absorption of carbohydrates, proteins, fats, vitamins, minerals, and trace elements [1, 2, 3, 4].

Lamblia attach to the surface of the mucous membrane using a sucking disc and lateral flagella, casting food substrate into the resulting gap between their body and the enterocyte's brush border. The substrate is subjected to the action of digestive enzymes located on the glycocalyx of the brush border, and the digestion products are absorbed by the parasite. By fixing onto the surface of enterocytes, lamblia block membrane digestion and cover the absorptive surface of the small intestine with their bodies; as a result, part of the food substrate remains undigested and enters the distal small intestine and further into the large intestine. In the development of diarrhea in giardiasis, processes of intense fermentation and gas formation in the large intestine, impaired absorption of water and salts, and changes in the composition of the intestinal microbiota are of significance [1, 2, 3, 4].

Lamblia trophozoites do not penetrate the intestinal tissues and do not form inflammatory infiltrates. It was previously erroneously believed that lamblia are capable of inhabiting the biliary tract and gallbladder [1, 2, 3, 5, 7].

During massive infection, up to 1 million trophozoites can be localized per 1 cm² of the small intestinal mucosa, which can cause mucosal subatrophy and shortening of intestinal microvilli with a disruption of their architecture. Repeated attachment and detachment of trophozoites from the mucous membrane contribute to the destruction of the microvillar glycocalyx, which also adversely affects the efficiency of membrane digestion. Metabolic products of lamblia, including certain proteases, in the presence of caspase-3, are capable of disrupting tight junctions between epithelial cells and promoting enterocyte apoptosis, which can lead to increased intestinal permeability [9, 12, 13].

Actively moving trophozoites irritate the neural receptors of the intestinal wall, which can contribute to the formation of pathological viscero-visceral reflexes with impaired gastrointestinal motility, the development of biliary dysfunction, and non-specific neurotic reactions [1, 3, 7].

During their life cycle, some lamblia trophozoites move with chyme into the middle and distal parts of the small intestine, where encystation processes are triggered. This process is finally completed in the colon.

Parasitism by lamblia causes local and general host defense responses. Parasite antigens selectively stimulate the production of interleukins (IL-4 and IL-5) by T-helper cells. IL-4 is a factor for the expression of CD23 markers, which are involved in the IgE-mediated cytotoxic response [9, 15].

In giardiasis, a mixed immune response is formed, including both antibody synthesis and Th1-type CD4+ T-cell reactions with the formation of circulating memory T cells with a Th1 phenotype. Adaptive immune responses are triggered by dendritic cells producing IL-6 and CD4+ T lymphocytes secreting TNF-α and IL-17. Under the influence of IL-17, epithelial cells enhance the secretion of antimicrobial peptides and activate IgA transport into the intestinal lumen; however, the efficiency of local immunity is not high because lamblia are capable of producing IgA proteases that destroy host IgA [9, 10, 15, 16].

Lamblia are non-invasive protozoa; therefore, significant influx of parasite antigens for the immune response does not occur, and a full-fledged humoral response is not formed, which determines the possibility of reinfections [1, 3, 5, 7].

In immunocompetent individuals, self-cure is often observed in giardiasis. In the presence of immunodeficiency, giardiasis can take a chronic course [1, 3, 5, 7].

The question of human body sensitization in giardiasis is currently of a debatable nature, and clinical practice shows that various kinds of allergic reactions and eosinophilia are mostly associated with concomitant pathology [1, 3].

1.3 Epidemiology of the Disease or Condition

According to WHO data, the global incidence of giardiasis is estimated at 280 million cases per year; however, according to experts, 10% to 20% of the world's total population is infected with lamblia. Infected people are significantly more numerous in developing countries (10-50%) than in developed countries (2-5%), which is associated with the high prevalence of asymptomatic carriers of the parasite, as well as the unavailability of developed infrastructure for safe water supply and centralized sanitation systems for a portion of the population [1, 3, 9, 10, 30]. Giardiasis is most widespread in African, Asian, and North American countries, where up to 200 million cases of the disease are registered per year [6, 9, 18].

In Russia the incidence of giardiasis is low, but in 2023 the incidence increased by 24.1%, with 23,278 cases registered (in 2022 – 18,651 cases). The incidence rate of giardiasis in 2023 was 15.87 per 100,000 population (in 2022 – 12.79 per 100,000 population). Compared to the multi-year average rates (34.7 per 100,000 population), the rate in 2023 decreased by 2.2 times.

In the age structure of those affected, the proportion of children under 17 years of age is 71.1% (54.42 per 100,000). The maximum incidence of giardiasis occurs in children aged 3-6 years (4,272 cases, a rate of 62.07 per 100,000 population), while among children aged 1-2 years, 1,356 cases were registered, at 47.50 per 100,000 population [19, 20].

The incidence of giardiasis is registered in all constituent entities of the Russian Federation, except for the city of Sevastopol, the Republic of Karachay-Cherkessia, and the Nenets Autonomous Okrug. Exceeding the national average is observed in 26 constituent entities of the country.

Constituent entities of the Russian Federation with the highest incidence rates of giardiasis in 2023 [20]

As a rule, sporadic cases of giardiasis are registered, but large outbreaks of waterborne giardiasis have been described in the literature [33].

The main source of infection is humans—a patient infected with lamblia or an asymptomatic carrier (lamblia carrier) [1, 3, 7]. The role of various animals as a source of human infection remains a subject of scientific debate, but modern molecular-biological research data indicate such a possibility.

The mechanism of transmission of the infection is fecal-oral. Mature, infective cysts are excreted in the feces of an infected person. The infectious dose for humans is low, ranging from 10 to 25 cysts. Ingestion of more than 25 cysts leads to 100% infection. The period of cyst excretion in humans begins on average on the 9th–12th day after infection; this process occurs in waves at intervals of 1 to 17 days and can last for many months. A patient with giardiasis poses the highest risk as a source of infection during the resolution phase of diarrhea, as the maximum number of cysts—about 1.8 million per 1 g of feces—is excreted during this period [1, 2, 3, 7]. Children under 9 years of age are most frequently infected with giardiasis, with boys being affected 2–3 times more often [1, 3].

High-risk groups for developing giardiasis among the adult population include travelers, individuals with low standards of hygiene and socioeconomic status, residents of institutional settings (hospitals, nursing homes, prisons), homosexual men, immunocompromised patients, individuals with weakened immunity (common variable immunodeficiency, hypogammaglobulinemia, HIV), patients with malabsorption syndrome, as well as representatives of certain professions (staff of childcare facilities, sewage and irrigation utilities, zoos, animal breeding farms, etc.) [1, 7].

Genetic studies reveal a "predisposition" to giardiasis in individuals with HLA antigens: B5, B14, DR3, DR4, and DR7 of the major histocompatibility complex. Haplotypes A1, A9, and B5 may serve as markers of predisposition [10, 22].

Modes of transmission of the causative agent: waterborne, contact-household, foodborne. Cases of the disease are most frequently recorded in the spring months (April–May) as well as in summer [1, 3, 5, 7].

Waterborne transmission is the primary route for giardiasis. Giardia cysts are detected in 80% of freshwater bodies (rivers, lakes, streams, ponds) and in 15% of wastewater samples. Water from unverified sources that fails to meet sanitary standards for microbial contamination frequently contains Giardia cysts [11, 19, 23]. Water from unverified sources that fails to meet sanitary standards for microbial contamination frequently contains Giardia cysts [11, 19, 23], which remain viable in fresh water at 4–20 °C for up to 3 months, and in dairy products for over 2 months [1, 7]. They are resistant to chlorine concentrations used for disinfecting tap water and are included in the list of test organisms used to verify the efficacy of water disinfection methods [1, 3, 5, 7]. Cysts are resistant to ultraviolet (UV) irradiation, but are rapidly killed by boiling; freezing at -13 °C reduces cyst viability to 1%. Air-drying of Giardia cysts for 24 hours leads to their complete destruction [7].

Contact-household transmission is mainly realized in childcare groups of younger age groups. The primary role as transmission factors can be played by the contaminated hands of children and staff, floors, carpets, toys, and the surfaces of furniture and restroom fixtures. In kindergartens, from 20% to 75% of children may be infected, who in turn can become sources for the formation of secondary family foci with the infection of family members, including adults [7, 14, 25].

Foodborne transmission is rare and occurs through the consumption of food products contaminated with Giardia cysts that have not undergone thermal processing (salads, puddings, etc.). As a rule, the source of infection in such outbreaks was a food service worker infected with Giardia [1].

Domestic insects have a certain significance in the spread of Giardia. In the intestines of flies, they remain alive from 30 hours to several days, and in the intestines of cockroaches—up to 8 days [5].

1.4 Features of Coding the Disease or Condition

A07.1 – Giardiasis [Lambliasis]

1.5 Classification of the disease or condition

Clinical forms of giardiasis:

• latent form (asymptomatic carriage);

• manifest form (with clinical manifestations).

By severity: mild, moderate, severe.

By course: acute, chronic.

1.6 Clinical presentation of the disease or condition

Asymptomatic giardiasis (latent, carriage) is not accompanied by clinical symptoms.

Symptomatic giardiasis (manifest) most commonly manifests with symptoms of gastrointestinal tract involvement.

The duration of the incubation period in manifest forms ranges from 7 to 28 days (average – 2 weeks).

Clinical signs and symptoms

The latent form is asymptomatic. In such cases, the only sign of giardiasis is the detection of Giardia cysts upon coproscopy. In immunocompetent individuals, parasite eradication occurs without treatment within several weeks. The entry of parasites into the gastrointestinal tract triggers a local immune response characterized by an increased concentration of secretory immunoglobulin A, leading to rapid destruction and elimination of the parasites [1, 3, 12, 13].

The manifest form of giardiasis typically presents with gastrointestinal dysfunction and nutritional deficiency. In some cases, symptoms of biliary dyskinesia develop, mainly in children and young adults [1, 3].

Clinically apparent giardiasis can be acute or chronic. The acute course lasts 5–7 days. At the onset of the disease, bloating and abdominal pain appear in the periumbilical region. This is followed by diarrhea ranging from 2–4 up to 6–10 times per day. The stool is foamy, foul-smelling, with a characteristic greasy sheen, devoid of blood and mucus. Symptoms of intoxication are mild. Patients occasionally complain of fatigue, decreased performance, and lowered emotional tone. Abdominal pain episodes (in the epigastrium, pyloroduodenal and periumbilical regions, and right hypochondrium) unrelated to food intake are frequently observed in giardiasis. The abdominal syndrome is often accompanied by nausea, eructation, heartburn, bitterness in the mouth, a feeling of gastric fullness, bloating, and decreased appetite. The severity of enteral disorders largely depends on age—the older the person, the less severe they are. Even without treatment, the majority of patients achieve clinical recovery confirmed by laboratory tests. Outcomes may include asymptomatic carriage (latent form) and a chronic course, which is characterized by alternating periods of exacerbation and subsidence of clinical symptoms.

Giardiasis typically follows a mild course. In infants, patients with concurrent gastrointestinal diseases, and those with severe immunosuppression, a moderate course of giardiasis may be observed, accompanied by prolonged wave-like episodes of diarrhea, the development of biliary dysfunction, and malabsorption [1, 3, 7, 14]. In children under 5 years of age, Giardia can cause severe acute diarrhea, while chronic infection may lead to weight loss and growth retardation [37]. Post-infectious lactase deficiency is common, occurring in 40% of cases [30].

Following giardiasis and parasite eradication, full recovery ensues, although in some cases irritable bowel syndrome, functional dyspepsia, or chronic fatigue syndrome may develop [31, 32, 33, 39, 42].

Differential diagnosis of giardiasis

When performing a differential diagnosis, other acute intestinal infectious diseases characterized by diarrhea must first be ruled out (escherichiosis, cryptosporidiosis caused by enteroinvasive strains, salmonellosis, shigellosis, yersiniosis, campylobacteriosis, clostridial infection, viral diarrhea, foodborne toxicoinfections, amebiasis, etc.).

Differential diagnosis of giardiasis is also performed with Crohn's disease, irritable bowel syndrome (IBS), lactose intolerance, celiac disease (gluten intolerance), acute appendicitis, ulcerative colitis, and other gastrointestinal diseases [1, 3, 10, 25, 26, 29].

Giardiasis is characterized by:

• absence of systemic intoxication symptoms;

• diarrhea up to 6–10 times per day; foamy, foul-smelling stool without blood and mucus, with a pungent odor;

• moderate pain localized in the upper abdomen;

• flatulence;

• wave-like course, tendency to recur;

Approaches to differential diagnosis are presented in Appendix A3.

2. Diagnostics, medical indications and contraindications for diagnostic methods

Diagnostic criteria

Diagnosis of giardiasis is carried out based on medical history, clinical examination, and laboratory tests, and aims to determine the nosological and clinical form, severity of the condition, and treatment indications [1, 2, 3, 4, 7, 8, 28, 29, 34]:

1. amnestic data – contact with patients having intestinal infections, poor personal hygiene, consumption of water from open water bodies, consumption of unboiled water from springs and wells, consumption of contaminated food;

2. complaints and physical examination data – absence of systemic intoxication signs, presence of flatulence, moderate pain primarily localized in the upper abdomen, signs of enteritis in the form of copious, loose, green, foamy stool with a pungent odor, wave-like course, tendency to recur;

3. laboratory tests: detection of vegetative forms of Giardia in liquid stool or duodenal contents; detection of cysts in mushy or formed stool.

2.1 Complaints and Anamnesis

• When taking the medical history, it should be determined whether the patient stayed 10–30 days prior to the disease onset in areas endemic for giardiasis, as well as in locations lacking adequate water supply and centralized sewerage. In children, parents should be asked about a history of animal contact and geophagia [1, 2, 3, 4, 7, 8, 27, 28, 34]:

GDR CLE 5Grade of recommendation C (level of evidence – 5)

Comments: It is recommended to pay attention to staying in areas where giardiasis is widespread, consuming unboiled water from open water sources, and staying in an outbreak focus of an acute diarrheal disease whose incubation period corresponds to that of giardiasis, in order to identify the source and transmission factors of the infection. It is important to clarify whether the patient belongs to a decreed (vulnerable/occupational) group. Whether there was close contact with animals [1, 2, 3, 4, 7, 8, 28, 29, 34].

• When taking the medical history, the presence or absence of complaints of fever, nausea, vomiting, diarrhea, the nature and frequency of stool, pain in the epigastric and umbilical regions, intestinal bloating, weight loss, and fatigue are ascertained. Attention is paid to the sequence and duration of the existing symptoms [1, 2, 3, 4, 7, 8, 28, 29, 34, 35]:

GDR CLE 5Grade of recommendation C (level of evidence – 5)

Comments: It is recommended to pay attention to the duration of diarrhea and the nature of the stool (foamy consistency, presence of blood and mucus) [1, 2, 3, 4, 7, 8, 28, 29, 34, 35].

2.2 Physical Examination

Comments: Changes in the skin and mucous membranes are absent in the majority of patients. In some cases, a moderate coating on the tongue is observed.

Comments: giardiasis is characterized by signs of enteritis, however, in some cases, symptoms characteristic of biliary dyskinesia may be detected. Liver size generally remains within normal limits.

2.3 Laboratory Diagnostics

At the diagnostic stage, indications for screening for giardiasis include [1, 3, 26, 46]:

1. diarrhea of undetermined etiology;

2. chronic gastrointestinal diseases;

3. impaired nutritional status, especially malnutrition.

Mandatory screening for giardiasis is required for the following groups:

1. children and staff of organized childcare facilities upon admission and thereafter once a year;

2. decreed population groups upon employment and thereafter once a year;

3. individuals who have been in contact with patients or parasite carriers;

4. inpatient and outpatient patients as clinically indicated.

2.3.1. Non-specific laboratory diagnostics

Comments: performed to assess baseline parameters and detect eosinophilia, which is characteristic of certain parasitoses.

Comments: performed to assess baseline parameters; in the presence of biliary dyskinesia, a slight increase in ALT, AST, ALP, and GGT activity may be observed.

Specific laboratory diagnostics

Comments: Molecular biological and bacteriological stool testing for the presence of pathogens belonging to the leading spectrum of acute intestinal infection pathogens is characterized by high sensitivity (over 90%) and specificity (over 95%), which significantly reduces the time required to establish an etiological diagnosis, determine etiological therapy tactics, and carry out anti-epidemic measures in the focus (in case of registered focal incidence). Since the clinical symptoms of infections caused by various enteropathogens largely overlap, it is difficult to differentiate the etiology of diarrhea in patients at the initial medical consultation stage.

Comments: Macro- and microscopic parasitological laboratory diagnostic methods are direct methods for detecting helminths, their fragments, eggs, and larvae; vegetative and cystic forms of pathogenic protozoa, the detection and identification of which do not require indirect research methods (MUK 4.2.735-99). Protozoological stool examination is the "gold standard" for laboratory diagnosis of giardiasis. Vegetative forms of Giardia are detected by the native smear method only in liquid freshly passed stool. In mushy and formed stool, cysts are detected. The most effective methods for their detection are formalin-ether sedimentation and Lugol's iodine smear. If the initial stool test is negative, individuals with suspected giardiasis are screened three times with an interval of 3-5 days. Feces samples can be placed in a container with a preservative (Turdyeva, Safaralieva, et al.) and then examined simultaneously. The sensitivity of the method is – 60-80% for a single test; – 80-90% for two tests; over 90% for three tests [2, 64].

Comments: The coproimmunodiagnostic method allows the detection of the specific Giardia antigen GSA-65 in feces. However, given the stated sensitivity of this test of 50-70% for a single test and 90% for three tests, false-positive results are frequently observed due to the transient presence of the antigen in the patient's feces, as well as the potential for cross-reactivity with other proteins.

IMPORTANT! A positive result of this test must be confirmed by the microscopic method using a triple stool examination for the presence of Giardia. Only after receiving confirmatory results can a definitive diagnosis of giardiasis (giardia carriage) be established [1, 3, 5].

Comments: Examination of duodenal contents is the most informative method. When giardiasis is suspected, bile portion "A" is examined to detect motile vegetative forms of Giardia. The biological material must be delivered to the laboratory for microscopic examination within 20–30 minutes after sampling.

Comments: Specific class M antibodies to Giardia antigens can be detected in blood serum from the 10th–14th day of the illness. Following sanitization, immunoglobulins M rapidly disappear, whereas immunoglobulins G may persist for 6–12 months. Serological blood tests for IgA, IgM, and IgG antibodies to Giardia antigens are indirect laboratory diagnostic methods and are recommended for use in seroepidemiological studies, as well as an additional diagnostic test to determine the body's immune response to pathogen invasion. These tests can yield both false-negative and false-positive results.

IMPORTANT! The detection of specific IgA, IgM, and IgG does not constitute a basis for confirming a definitive diagnosis of giardiasis and prescribing antiparasitic therapy. The diagnosis can only be confirmed by the microscopic method of parasite detection in feces!!! [1, 3, 5, 7].

Comments: The collection of material and its research methods are carried out in accordance with MUK 4.2.3145-13. The method makes it possible to detect the presence of certain gastrointestinal helminthiases in the patient, which may present with symptoms similar to giardiasis, or to rule out their presence.

2.4 Instrumental Diagnostics

Comments: Ultrasound allows for the detection of certain signs of biliary dyskinesia, as well as other pathological changes: gallbladder enlargement, presence of sediment structures, gallstones, their number, size, localization, etc.

2.5 Other Procedures

Comments: it is recommended to perform differential diagnosis between giardiasis and other diseases presenting with diarrheal syndrome. Approaches to differential diagnosis are presented in Appendix A3.

3. Treatment, including drug and non-drug therapies, diet therapy, and pain management

When prescribing treatment for patients with giardiasis, it is necessary to consider the clinical course variant, all comorbid conditions, and the patient's age.

Infected individuals are subject to treatment in outpatient or inpatient settings based on their informed voluntary consent and taking into account the right to refuse medical intervention. Etiotropic therapy is carried out only after establishing a definitive diagnosis, which must be confirmed by direct microscopic methods [1, 3, 5, 7, 23].

Outpatient or general inpatient regimen. Treatment of giardiasis is carried out mainly on an outpatient basis and does not require isolation measures. Treatment must be comprehensive and include specific antiparasitic drugs and, if necessary, pathogenetic therapy aimed at correcting functional disorders of the digestive system.

Etiotropic (antiparasitic) therapy

Comments: 5-Nitroimidazoles are drugs of choice for the treatment of giardiasis.

• Metronidazole** orally: adults 250 mg 3–4 times a day for 5 days; children 2–5 years old at a dose of 250 mg (in 2 doses) for 5 days; children 5–10 years old at a dose of 375 mg per day (in 2 doses) for 5 days; children 10–15 years old 250 mg 2 times a day for 5 days.

• Ornidazole orally: adults at a dose of 1.5 g once in the evening; children with a body weight of 20–35 kg at a dose of 40 mg/kg of body weight per day, over 35 kg at a dose of 1.5 g per day once. Contraindicated in children under 3 years of age and with a body weight of less than 20 kg.

• Secnidazole orally: adults once at a dose of 1.5–2.0 g; children from 3 years of age at a dose of 30 mg/kg of body weight per day once, washing down with a small amount of liquid. Course duration is 1 day.

• Tinidazole orally: adults at a dose of 2 g orally once; children over 12 years of age at a dose of 50–75 mg/kg of body weight per day (not exceeding 2 g) once after meals. Course duration is 1 day.

Second-line drugs:

• Albendazole orally: adults and children over 3 years of age with a body weight of more than 10 kg, 400 mg once daily for 3 days. Children with a body weight of less than 10 kg – 200 mg once daily in suspension form for 5 days. Tablets are contraindicated in children under 3 years of age.

• Nifuratel orally: adults at a dose of 400 mg 2–3 times a day; children at a dose of 15 mg/kg of body weight 2 times a day after meals. Course duration is 7 days. Contraindicated in children with a body weight of less than 20 kg.

• Furazolidone orally: adults at a dose of 0.1 g 4 times a day; children from 3 years of age at 10 mg/kg of body weight per day in 3–4 doses. The maximum single dose for adults is 200 mg, daily dose – 800 mg. Course duration is 5–10 days. Contraindicated in children under 3 years of age.

5-Nitroimidazoles are the most frequently used first-line drugs. Metronidazole** has a relatively short half-life and requires a 5-day course of administration. Tinidazole, secnidazole, and ornidazole have a longer half-life, so single doses are highly effective against Giardia. The efficacy of drugs from the 5-nitroimidazole group ranges from 70% to 90%.

Albendazole at recommended doses shows an efficacy of 83–96%.

Nifuratel has a broad spectrum of activity against a large group of bacteria, protozoa, and fungi. Its efficacy against giardiasis is over 90%.

Furazolidone currently has limited use in the treatment of giardiasis; its efficacy is over 88% [1, 3, 7, 37].

All antiparasitic drugs have various side effects; therefore, treating individuals infected with Giardia (especially children) without parasitological confirmation of giardiasis is unacceptable. Treatment for contacts is carried out only upon detection of the pathogen, regardless of clinical manifestations.

Drugs recommended for the treatment of giardiasis in children [29]

Initial therapy: Nifuratel, Albendazole, Metronidazole**, Furazolidone

Alternative therapy: Tinidazole

Reserve drugs: Ornidazole, Secnidazole

Comments: in addition to clinical improvement and disappearance of diarrhea, the criteria for the effectiveness of giardiasis treatment are 3 negative results of coprological examination (using Turdyev, Safaraliev, or Barrow preservatives) performed at intervals of 2–3 days one week after antiprotozoal therapy [1, 3, 5, 14].

3.1.2 Pathogenetic and symptomatic therapy

Comments: The probiotic Saccharomyces boulardii CNCM I-745 exhibits direct antigiardial activity. The use of Saccharomyces boulardii CNCM I-745 or probiotics (Lactobacillus acidophilus, Bifidobacterium infantis, Enterococcus faecium) concomitantly with antigiardial drugs is more effective in treating giardiasis than monotherapy with antiparasitic agents. Due to the disruption of the intestinal microbiota composition in all patients with giardiasis, the administration of probiotics containing Bifidobacterium bifidum, Bifidobacterium longum, Bifidobacterium animalis subsp. lactis (BB-12), Lactobacillus rhamnosus GG, and Streptococcus thermophilus TH-4 is recommended to correct this imbalance. According to preclinical and clinical studies, probiotics can protect against parasite-induced mucosal damage by enhancing antioxidant capacity, suppressing oxidative products, and regulating systemic and local immune responses. Probiotics may also reduce the parasite load of G. duodenalis through a direct destructive effect on the parasite and the inhibition of trophozoite proliferation and growth. [14, 27, 40, 41, 43, 44].

Comments: The recommended dose of ursodeoxycholic acid** is 10 mg/kg/day. For children with a body weight of less than 47 kg, the drug is prescribed in the form of a suspension. For adults, ursodeoxycholic acid** preparations are prescribed at 500–1000 mg/day (at bedtime) orally.

3.1.3 Diet therapy

The organization of therapeutic dietary nutrition for patients with giardiasis during inpatient treatment in medical organizations is carried out in accordance with the Orders of the Ministry of Health of the Russian Federation No. 330 of August 5, 2003, "On measures to improve therapeutic nutrition in healthcare institutions of the Russian Federation," No. 395n of June 21, 2013, "On approval of therapeutic nutrition standards," and No. 1008n of September 23, 2020, "On approval of the procedure for providing patients with therapeutic nutrition."

Comments: in the acute period and during etiotropic therapy, Diet No. 4 is recommended, aimed at creating conditions that impair Giardia reproduction (restriction of carbohydrates and exclusion of dairy products); introduction of foods that act as nutritional sorbents (porridges, bran, baked apples, pears, dried fruits, vegetable oil). Foods and dishes that cause mechanical and chemical irritation of the gastrointestinal tract (milk, canned food, smoked meats, spicy and seasoned dishes, raw vegetables and fruits) are completely excluded from the diet. Food should be taken fractionally, 4–6 times a day. Mucilaginous soups, minced or pureed meat dishes, boiled lean fish, omelets, porridges, and cottage cheese are recommended. Food should be consumed every 4–6 hours and should not be heavy. The use of grated raw apples is indicated. The duration of the diet is individual and determined by the patient's condition and well-being. Expansion of the diet can begin on the 2nd–5th day after the cessation of diarrhea by prescribing Table No. 5.

Dishes are prepared boiled, stewed, baked, pureed or non-pureed, and steamed. Food temperature ranges from 15 to 60–65 °C. Free fluid 1.5–2 L. Fractional meal schedule, 4–6 times a day. Proteins 110–120 g, including animal proteins 45–60 g; total fats 80–90 g, including vegetable fats 30 g; total carbohydrates 250–350 g, including mono- and disaccharides 30–40 g; energy value 2080–2690 kcal [38].

4. Medical Rehabilitation and Sanatorium-Resort Treatment

Rehabilitation measures are not indicated for giardiasis.

5. Prevention and Dispensary Observation

Prevention of giardiasis is aimed at reducing the risks of infection and is carried out in accordance with the requirements of guidelines MU 3.2.3966-23 [1, 2, 4, 5].

• Isolation of a patient with giardiasis is not required, as the person does not pose an epidemiological hazard.

Level CLevel 5Level of recommendation evidence C (reliability level of evidence – 5).

Comment: transmission of the pathogen from person to person under normal conditions is completely ruled out.

5.1 Specific prevention

Not performed.

5.2 Non-specific prevention

Comments: Detection of patients with giardiasis is carried out: upon seeking medical care in healthcare facilities; during medical examinations and monitoring of individuals who have been in contact with patients and Giardia carriers; during unscheduled parasitological examinations of designated population groups in the event of an epidemiological emergency regarding acute intestinal infection in the given territory or facility. The necessity of their implementation, frequency, and scope are determined by Rospotrebnadzor specialists.

5.3 Clinical follow-up (dispensary observation)

• Follow-up (dispensary observation) is limited to quality control of treatment effectiveness. 5–6 days after the completion of therapy, a two- to three-stool coprological analysis is indicated at intervals of 1–2 days. If results are positive, repeat therapy is indicated. If test results are negative, the patient is discharged from follow-up observation. Designated workers may be cleared for work, and children attending organized groups may return to their childcare facilities [3, 10, 12, 27, 35, 36].

Level CLevel 5Level of recommendation evidence C (reliability level of evidence – 5).

Comments: Food industry workers and equivalent personnel with positive results from control parasitological examinations conducted after a repeat course of treatment are transferred to other work not related to the production, storage, transportation, and sale of food products and water supply (until recovery). If Giardia excretion persists for more than 3 months after the illness, they are permanently transferred to work not involving food products and water supply as chronic carriers.

6. Organization of Medical Care

Comment: The following patients are subject to hospitalization based on clinical and epidemiological indications:

1. belonging to risk groups (HIV-infected individuals, patients with immunodeficiency states);

2. with protracted and chronic courses of giardiasis during exacerbations, suffering from severe comorbid diseases;

3. designated groups (food industry workers and equivalent personnel) when outpatient treatment cannot be provided.

Comments: Food industry workers and equivalent personnel are cleared for work only after therapy quality control (see section 5.3).

Patients not belonging to the above categories are cleared for work based on a recovery certificate and a single negative result of a parasitological stool examination.

Medical care is provided in the form of:

• planned medical care.

Conditions for the provision of medical services

Medical care is provided in the form of:

• primary health care;

• specialized medical care, including high-tech medical care.

Medical care for adult patients with giardiasis may be provided in the following settings:

• outpatient (in settings not providing round-the-clock medical observation and treatment);

• in a day hospital (under conditions providing medical observation and treatment during the day, not requiring round-the-clock medical observation and treatment);

• inpatient (in settings providing round-the-clock medical observation and treatment).

Primary health care is provided to patients on an outpatient basis and in a day hospital setting.

Primary paramedic-led health-care in outpatient settings is provided at feldsher-midwifery stations.

Primary health care is provided by a district general practitioner, general practitioner (family physician) in an outpatient setting.

Primary specialized primary health care is provided by an infectious disease specialist of a medical organization providing medical care to outpatients.

Specialized, including high-tech, medical care is provided in an inpatient setting by infectious disease specialists and other specialist physicians and includes the prevention, diagnosis, treatment of diseases and conditions requiring the use of special methods and complex medical technologies, as well as medical rehabilitation.

Treatment of patients is carried out in an inpatient setting upon referral by a general practitioner, general practice physician (family physician), infectious disease physician, or medical personnel who identified the giardiasis.

Criteria for Evaluating the Quality of Medical Care

References

Appendix A1. Working Group Composition

1. Gorelov, A.V. – Academician of the Russian Academy of Sciences, Doctor of Medical Sciences, Professor, Deputy Director for Scientific Work at the Central Research Institute of Epidemiology of Rospotrebnadzor, Head of the Department of Infectious Diseases and Epidemiology at the A.I. Evdokimov Moscow State University of Medicine and Dentistry of the Russian Ministry of Health, Chairman of the Board of the Academician V.I. Pokrovsky National Association of Infectious Disease Specialists.

2. Anokhin, Vladimir Alekseevich – Doctor of Medical Sciences, Professor, Head of the Department of Pediatric Infections at Kazan State Medical University of the Russian Ministry of Health

3. Galeyeva, Nelly Vasilyevna – Candidate of Medical Sciences, Associate Professor at the Department of Infectious Diseases, Federal State Budgetary Educational Institution of Higher Education "Kazan State Medical University" of the Ministry of Health of the Russian Federation.

4. Gilmullina, Fayruza Saubanovna – Candidate of Medical Sciences, Associate Professor at the Department of Infectious Diseases, Federal State Budgetary Educational Institution of Higher Education "Kazan State Medical University" of the Ministry of Health of the Russian Federation.

5. Kozlov, Konstantin Vadimovich – Doctor of Medical Sciences, Professor, Head of the Department of Infectious Diseases (with a course of medical parasitology and tropical medicine) with a clinic of infectious diseases at the S.M. Kirov Military Medical Academy of the Ministry of Defense of the Russian Federation.

6. Kozlov, Sergey Sergeyevich – Doctor of Medical Sciences, Professor at the Department of Infectious Diseases (with a course of medical parasitology and tropical medicine) with a clinic of infectious diseases at the S.M. Kirov Military Medical Academy of the Ministry of Defense of the Russian Federation; Professor at the Department of Adult Infectious Diseases and Epidemiology at the Federal State Budgetary Educational Institution of Higher Education "Saint Petersburg State Pediatric Medical University" of the Ministry of Health of the Russian Federation.

7. Kravchenko, Irina Eduardovna – Doctor of Medical Sciences, Associate Professor, Professor at the Department of Infectious Diseases, Federal State Budgetary Educational Institution of Higher Education "Kazan State Medical University" of the Ministry of Health of the Russian Federation.

8. Morozov, Yevgeny Nikolayevich – Doctor of Medical Sciences, Professor at the Department of Medical Parasitology and Virology, Federal State Autonomous Educational Institution of Higher Education "I.M. Sechenov First Moscow State Medical University of the Ministry of Health of the Russian Federation" (Sechenov University).

9. Nikolayeva, Irina Venidiktovna – Doctor of Medical Sciences, Professor, Head of the Department of Infectious Diseases, Federal State Budgetary Educational Institution of Higher Education "Kazan State Medical University" of the Ministry of Health of the Russian Federation.

10. Usenko, Denis Valeryevich – Doctor of Medical Sciences, Head of the Educational Center, Leading Researcher at the Clinical Department of Infectious Pathology, Central Research Institute of Epidemiology of Rospotrebnadzor.

11. Fatkullina Guzel Roaldovna – Candidate of Medical Sciences, Associate Professor of the Department of Pediatric Infections, Kazan State Medical University of the Russian Ministry of Health

12. Khaliullina Svetlana Viktorovna – Doctor of Medical Sciences, Professor of the Department of Pediatric Infections, Kazan State Medical University of the Russian Ministry of Health.

13. Chulanov Vladimir Petrovich, Doctor of Medical Sciences, Professor, Deputy Director for Science and Innovative Development, National Medical Research Center for Phthisiopulmonology and Infectious Diseases of the Russian Ministry of Health.

14. Esaulenko Elena Vladimirovna, Doctor of Medical Sciences, Professor, Head of the Department of Adult Infectious Diseases and Epidemiology, Federal State Budgetary Educational Institution of Higher Education "Saint Petersburg State Pediatric Medical University" of the Ministry of Health of the Russian Federation.

All members of the working group are members of the Pokrovsky National Association of Infectious Disease Specialists (NAIDS).

There is no conflict of interest.

Appendix A2. Methodology for Developing Clinical Guidelines

Target audience of the clinical guidelines:

1. Infectious disease specialist;

2. General practitioner (internist);

3. Gastroenterologist;

4. General practitioner;

5. Medical students, residents, postgraduate students.

In these clinical guidelines, all data are ranked by level of reliability (evidence) depending on the quantity and quality of studies on the issue.

Determination of levels of evidence certainty and grades of recommendation for diagnostic interventions

Table А1 – Scale for assessing the levels of evidence (LE) for diagnostic methods (diagnostic interventions)

¹The standard accepted design for clinical studies of diagnostic interventions is a cross-sectional study design, in which the diagnostic method under investigation and the reference method, which is the "gold standard" for diagnosing the disease or condition under study, are applied in parallel and under identical conditions to each included patient. The investigational and reference methods must be applied independently of each other (i.e., the investigational method cannot be part of the reference method) and must be interpreted by the investigator without knowledge of the results of the other method (blinding is recommended).

Table A2 – Scale for assessing the grades of recommendation (GR) for prevention, diagnosis, treatment, and medical rehabilitation methods, including those based on natural therapeutic factors (preventive, diagnostic, therapeutic, and rehabilitative interventions)

Table P3. Possible combinations of LCE and GGR for diagnostic interventions

Determination of the level of evidence reliability and recommendation strength for therapeutic, rehabilitation, and preventive interventions

Table A4 – Scale for assessing the levels of evidence (LE) for methods of prevention, treatment, and medical rehabilitation, including those based on natural therapeutic factors (preventive, therapeutic, and rehabilitative interventions)

Procedure for updating clinical guidelines

Clinical guidelines are updated every 3 years.

Appendix A3. Reference Materials

These clinical guidelines were developed taking into account the following regulatory legal documents:

1. Federal Law of the Russian Federation No. 326-FZ dated November 29, 2010, "On Compulsory Medical Insurance in the Russian Federation."

1. Federal Law No. 323-FZ of November 21, 2011, "On the Fundamentals of Protecting the Health of Citizens in the Russian Federation".

2. Order of the Ministry of Health and Social Development of Russia No. 494 of August 9, 2005, "On the Procedure for the Use of Medicinal Products in Patients for Vital Indications".

3. Order of the Ministry of Health and Social Development of Russia No. 804n of October 13, 2017 (as amended on September 24, 2020, with amendments of October 26, 2022) "On Approval of the Nomenclature of Medical Services".

4. Order of the Ministry of Health and Social Development of Russia No. 69n of January 31, 2012, "On Approval of the Procedure for Providing Medical Care to Adult Patients with Infectious Diseases".

5. Order of the Ministry of Health of Russia No. 205n of May 20, 2023, "On Approval of the Nomenclature of Positions of Medical Workers and Pharmaceutical Workers".

6. Order of the Ministry of Health of Russia No. 700n of October 7, 2015, "On the Nomenclature of Specialties of Specialists with Higher Medical and Pharmaceutical Education".

7. Order of the Ministry of Labor of Russia No. 585n of August 27, 2019, "On Classifications and Criteria Used in Carrying Out Medical and Social Expertise of Citizens by Federal State Institutions of Medical and Social Expertise".

8. Order of the Ministry of Health of Russia No. 203n of May 10, 2017, "On Approval of Criteria for Assessing the Quality of Medical Care".

9. SanPiN 3.3686-21 "Sanitary and Epidemiological Requirements for the Prevention of Infectious Diseases" XXIV. Prevention of Acute Intestinal Infections (Registered with the Ministry of Justice of Russia on February 15, 2021, N 62500)

10. Order of the Ministry of Health of the Russian Federation No. 906n dated November 12, 2012, "On Approval of the Procedure for Providing Medical Care to the Population Profiled in 'Gastroenterology'."

11. GOST R 52600-2006 "Patient Management Protocols. General Provisions" (Order of the Federal Agency on Technical Regulating and Metrology dated December 5, 2006, No. 288).

12. International Statistical Classification of Diseases and Related Health Problems (ICD-10).

13. Methodological Guidelines MU 4.2.2039-05. 4.2. Control Methods. Biological and Microbiological Factors. Technique for Collection and Transport of Biological Materials to Microbiological Laboratories. Methodological Guidelines" (approved by Rospotrebnadzor on December 23, 2005).

14. Methodological Guidelines MUK 4.2.2746-10 "Procedure for Using Molecular Genetic Methods in the Investigation of Acute Intestinal Infection Foci with Group Morbidity."

15. MU 1.3.2569-09 "Organization of Work of Laboratories Using Nucleic Acid Amplification Methods When Working with Material Containing Pathogenicity Microorganisms of Groups I-IV."

16. MU 4.2.3145-13 4.2 Laboratory Diagnostics of Helminthiases and Protozooses: Methodological Guidelines. – Moscow: FBUZ "Federal Center for Hygiene and Epidemiology" of Rospotrebnadzor. – 154 p.

17. MU 3.2.3966-23 3.2. Prevention of Parasitic Diseases. Epidemiological Surveillance and Prevention of Giardiasis. Methodological Guidelines (approved by the Chief State Sanitary Doctor of the RF on September 5, 2023).

18. MUK 4.2.3533-18 4.2. Immunological Methods for Laboratory Diagnostics of Parasitic Diseases: Methodological Guidelines. – Moscow: Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing, 2018. – 47 p.

19. Order of the Ministry of Health of the Russian Federation No. 330 dated August 5, 2003, "On Measures to Improve Clinical Nutrition in Healthcare Facilities of the Russian Federation."

20. Order of the Ministry of Health of the Russian Federation No. 395n dated June 21, 2013, "On Approval of Medical Nutrition Standards."

21. Order of the Ministry of Health of the Russian Federation No. 1008n dated September 23, 2020, "On Approval of the Procedure for Providing Patients with Therapeutic Nutrition."

22. Order of the Ministry of Health of the Russian Federation No. 203n dated May 10, 2017, "On Approval of Criteria for Assessing the Quality of Medical Care."

Potential transmission routes and factors of the giardiasis causative agent

Note: * – Assessment of the strength of recommendations according to the rating scheme.

Algorithm for patient examination depending on the timing and clinical manifestations of giardiasis

Differential diagnosis of giardiasis with other infectious diseases of the gastrointestinal tract

Appendix B. Physician Action Algorithms

Appendix C. Patient Information

Giardiasis is a widespread and frequently occurring parasitic human disease globally. Giardiasis may occur under the "mask" of other diseases, or be completely asymptomatic, with the infection being detected incidentally in such individuals.

The causative agents of the disease exist in two forms: the vegetative form (trophozoite), which inhabits the upper parts of the intestine, and the cyst, a resting form that ensures the survival of the parasite in the external environment: in water, including water bodies and sewage (up to several months), on food products (from several hours to several days), and in sand (up to 9-12 days). Giardia cysts (like helminth eggs) are resistant to standard chlorine concentrations and ultraviolet radiation, and are able to withstand freezing (down to -15 °C) and heating up to 50 ⁰C, but are rapidly killed by boiling.

The source of infection is an infected person, less commonly an animal (dogs, cats, rabbits, guinea pigs, beavers, etc.). Human infection occurs via the fecal-oral route when cysts enter the gastrointestinal tract. In the intestine, cysts transform into vegetative forms that colonize the lumen of the small intestine, causing digestive dysfunctions, reducing digestive efficiency, and causing diarrhea. In the intestine, some vegetative forms enter the large intestine and transform into cysts, which are excreted into the environment with feces.

Cyst excretion occurs in a wave-like, intermittent manner. Periods of excretion alternate with periods of absence. Spontaneous clearance of the body from Giardia is frequently observed.

The pathogen is transmitted to humans through contaminated water, food, hands, and various objects. Insects (flies, cockroaches, mealworms, dung beetles) can also contribute to the spread of Giardia cysts.

Water is the main factor through which infection occurs in humans and animals. People can become infected by consuming untreated water from unverified water sources (springs, streams, lakes, etc.) or ice made from such water. There is a risk of contracting the disease after swimming in open water bodies and pools.

There is a risk of infection through raw vegetables and fruits that are poorly washed or washed with contaminated water.

Sometimes giardiasis can be transmitted through household contact within families or children's groups (nurseries, kindergartens, schools). If a child or adult does not wash their hands properly after visiting the restroom, they can transmit the infection via toys, furniture, dishes, or by sharing a towel, on which cysts remain viable for up to 2 doses (up to 2 days). Bad habits play a significant role in infection: putting fingers in the mouth, biting nails, pencils, pens, etc.

Human susceptibility to the infection is high. Children and immunocompromised individuals are especially easily infected. Re-infection is possible after recovery.

Affected populations. The overwhelming majority of patients are children, due to the characteristics of their digestion and the lack of necessary hygiene skills. Children in the younger and middle age groups fall ill more often. Among adults, there is a high risk of infection in individuals lacking personal hygiene skills, as well as among certain occupational risk groups.

Detection of patients with giardiasis is carried out during preventive, routine, preliminary (upon hiring), and periodic examinations, according to clinical and epidemiological indications, during medical observation of individuals who have been in contact with a patient or carrier of giardiasis.

The diagnosis of giardiasis is established based on the clinical signs of the disease and the results of laboratory examination. Parasitological examinations of feces and duodenal contents are the mainstay of laboratory diagnosis. The presence of inconsistent, intermittent cyst excretion in the latent course of the disease requires repeated examinations (at least 3) at intervals of 2-5 days.

As additional diagnostic methods for giardiasis, immunological (serological) methods, which are largely informative in nature, can be used. They are based on the detection of antibodies in the blood specific to Giardia antigens. Antibodies can be detected both in individuals at the peak of the disease and in those who have recently had the infection.

Clinical presentation. Giardiasis can occur in manifest (acute, less commonly chronic) and asymptomatic forms (giardia carriage).

In manifest giardiasis, patients complain of bloating and rumbling in the intestines, epigastric pain, and diarrhea.

Acute giardiasis is characterized by loose stools, bloating, and abdominal pain. The acute period usually lasts a few days, after which symptoms may disappear on their own and then return, which occurs during the transition to the chronic form, more commonly detected in immunocompromised individuals.

Chronic giardiasis is accompanied by recurrent loose stools, cramping abdominal pain, nausea, alternating constipation and diarrhea, decreased appetite, and impaired general condition (malaise, irritability, headaches, rapid fatigue). Furthermore, children lag behind in physical development and have a weight below normal.

Clinical manifestations of the disease are detected in 80% of infected individuals, but asymptomatic carriage is also possible. Parasite carriers pose a threat to people around them because they do not receive treatment and shed the pathogen into the environment for years.

The combination of giardiasis with other gastrointestinal diseases mutually worsens the course of the disease.

Suspecting giardiasis is quite difficult, therefore diagnosis should be handled by specialists.

Prophylaxis. To prevent giardiasis infection, it is necessary to follow a number of preventive measures:

• Drink only boiled or factory-bottled water.

• Raw vegetables and fruits should preferably be rinsed with boiled water or scalded with boiling water before consumption.

• It is recommended to use water filters capable of retaining particles with a diameter of 5 microns.

• Avoid purchasing food from street vendors and eating in establishments with questionable adherence to hygiene standards.

• Personal hygiene rules must be observed, and necessary hygienic skills should be instilled in children.

• In children's groups and public restrooms, there must be special soap dishes, individual, or preferably disposable towels or wipes.

Knowledge and observance of preventive measures will help prevent giardiasis infection and the development of the disease.

Dietary recommendations for manifest giardiasis

1. General principles.

In giardiasis, 5-6 meals a day are recommended, as frequent intake of small portions promotes better bile excretion, which has a detrimental effect on Giardia.

The diet should be predominantly protein-based, with restricted intake of easily digestible carbohydrates.

The diet should be low-lactose. Acidic drinks and fermented milk products are indicated, as an acidic environment inhibits the reproduction of Giardia.

The diet should contain a high amount of dietary fiber, both naturally in foods and through the addition of bran.

2. Permitted foods

Easily emulsifiable fats: butter, vegetable oils (olive, sunflower, corn).

Vegetarian soups with vegetables, groats, noodles, and fruit soups. Non-rich meat broths with vegetables. Lean meats (beef, veal, rabbit) in the form of steam cutlets, meatballs, quenelles, and soufflés. Dietary and cooked sausages. Beef sausages.

Lean fish: cod, pikeperch, wild carp, navaga.

Dairy products: fresh cottage cheese, preferably low-fat, homemade. Kefir, sour milk, acidophilus milk, bio-yogurts. Sour cream – only as a dressing for dishes.

Eggs – primarily for cooking purposes. Protein omelet, or soft-boiled no more than 1 piece per day.

Vegetables and greens – fresh, raw (carrots, cabbage, cucumbers, tomatoes). Boiled (mashed potatoes, pureed beets, green peas, cauliflower and other cabbage varieties, zucchini, pumpkin, greens). Onions only boiled. Fermented and salted pickles are allowed.

Fruits: sweet, ripe. Fruit dishes. Mousses, jellies, gravies. Dried apricots, prunes, raisins (seedless). Sour fruit drinks from cranberries and lingonberries, freshly squeezed juices.

Sweets – honey, marshmallows, marmalade, non-rich shortbread cookies.

Appetizers – salads, vinaigrettes, jellied fish with gelatin, soaked herring (occasionally).

Porridge – buckwheat, oatmeal, rice, wheat, etc.

3. Prohibited foods

Refractory animal fats, lard, culinary fats, margarine.

Soups: strong meat, fish, or mushroom broths, rich cabbage soups and borscht.

Fatty meats – pork, ham, fatty sausages, pork sausages, frankfurters, canned meat.

Fatty fish – trout, salmon, sturgeon, etc.

Cream, fatty gravies and sauces, sharp cheeses.

Hard-boiled and raw eggs, fried eggs (sunny-side up).

Beans, peas, lentils, sorrel, garlic, radishes, and turnips rich in essential oils.

Unripe raw fruits, nuts, almonds.

Chocolate, candies, cakes, pastries, ice cream, creams, carbonated beverages.

Spicy condiments (pepper, mustard, vinegar, horseradish, mayonnaise).

Smoked products, mushrooms.

Appendix G. Assessment Scales, Questionnaires, and Other Evaluation Tools

No.