Taxonomy and classification of plasmodia
In medical practice, the term "malaria" is a general one. In fact, it encompasses four distinct diseases caused by different species of pathogens.
All of them belong to the subkingdom Protozoa, phylum Apicomplexa, genus Plasmodium (which includes the subgenera Laverania and Plasmodium).
In modern practice, diagnoses are formulated according to ICD-10 requirements, although traditional clinical names are still frequently used in Russian medicine.
| Pathogen species | ICD-10 form | Traditional name |
|---|---|---|
| Plasmodium falciparum | Falciparum malaria | Tropical malaria |
| Plasmodium vivax | Vivax malaria | Tertian malaria |
| Plasmodium ovale | Ovale malaria | Ovale malaria |
| Plasmodium malariae | Malariae malaria | Quartan malaria |
Epidemiology and distribution
Malaria is transmitted via vectors. It is a global public health problem, with about half of the world's population living in at-risk areas. Between 200 and 250 million cases of infection are registered annually. Mortality reaches 1–2 million people per year, the vast majority being children under five years of age from sub-Saharan African countries. Economic losses on the African continent are estimated at 2 billion US dollars annually.
The problem remains relevant in the Russian Federation due to the active importation of the infection by tourists and migrants (e.g., from Tajikistan, Azerbaijan, Indonesia). Cases of "airport" and even "indigenous" malaria occur. The lack of specific chemoprophylaxis before traveling to endemic regions is the main mistake made by travelers.
Life cycle and pathogenesis
The pathogenesis of clinical manifestations of malaria is directly related to the stages of development of the plasmodium. In the human body, the pathogen goes through several stages:
- Tissue (hepatic) schizogony. Multiplication of the parasite in hepatocytes.
- Erythrocytic schizogony. Invasion of erythrocytes by plasmodia, their destruction, and the release of new parasites into the bloodstream.
- Gametocytogony. Formation of the sexual forms of the pathogen.
Massive destruction of erythrocytes triggers a typical malaria paroxysm: the patient experiences severe chills, temperature rises to 39–40°C, and then drops sharply, accompanied by profuse sweating. The destruction of red blood cells leads to hemolytic anemia, and the immune system response leads to hepatosplenomegaly (enlargement of the liver and spleen).
Clinical presentation and complications
The classic manifestation of the infection is the regular alternation of fever paroxysms. For example, in tertian malaria, paroxysms occur every other day, and during the inter-paroxysmal period (apyrexia), the patient's condition may remain relatively satisfactory.
Infection caused by Plasmodium falciparum is particularly dangerous. It can lead to specific severe complications:
- Cerebral malaria;
- Acute renal failure;
- Acute liver failure.
In turn, the pathogen Plasmodium malariae is associated with the development of severe nephrotic syndrome.
Principles of laboratory diagnostics
Upon detecting the triad of symptoms (fever with chills + hepatosplenic syndrome + anemia), a physician is obligated to rule out malaria, especially if the epidemiological history includes a stay in tropical countries.
To confirm the diagnosis, the following are prescribed:
- Microscopy of a thick drop and thin peripheral blood smear.
- Staining of preparations using the Romanowsky-Giemsa method.
- Quantitative assessment: upon detecting plasmodia, the laboratory technician must determine their concentration per 1 µl of blood.
- Evaluation of the complete blood count: leukopenia, relative lymphocytosis, neutropenia, and decreased hemoglobin levels are characteristic.
Differential diagnosis
The physician must keep in mind that fever and hepatosplenic syndrome occur not only with plasmodium infection. The disease must be differentiated from influenza, typhoid fever, leptospirosis, sepsis, visceral leishmaniasis, brucellosis, and Hodgkin's lymphoma. A patient with suspected malaria is subject to mandatory hospitalization in an infectious diseases department for emergency anti-malarial and pathogenetic therapy.
Briefly: answers to topical questions
What pharmacological drugs are used for etiotropic treatment of malaria?
For etiotropic treatment of malaria, drugs acting on different stages of the plasmodium life cycle are used:
- Blood schizonticides (acting on erythrocytic forms) — chloroquine, quinine, mefloquine, artemisinin, atovaquone, doxycycline, tetracycline, clindamycin, sulfonamides, pyrimethamine, proguanil.
- Tissue schizonticides (acting on tissue forms in the liver) — primaquine, pyrimethamine.
- Gametocides (acting on sexual forms) — pyrimethamine, primaquine.
For the treatment of severe and complicated forms, intravenous infusions of quinine dihydrochloride or parenteral administration of artemisinin derivatives are used.
Which genus of mosquitoes is the vector and definitive host of the malaria plasmodium?
The vector and definitive host of the malaria plasmodium are exclusively female mosquitoes of the genus Anopheles. In their stomach and body, the pathogen undergoes the sexual stage of its life cycle — sporogony. Humans act merely as an intermediate host for the plasmodium, within which asexual reproduction (schizogony) takes place. The vector becomes infected when ingesting human blood containing gametocytes.
What happens at the sporogony stage in the life cycle of the plasmodium?
At the sporogony stage, the sexual development of the parasite takes place inside the female mosquito's body. The process includes the following stages:
- Fusion of male and female gametocytes that entered the insect's stomach with the patient's blood.
- Formation of a zygote from the fused gametes.
- Multiple divisions and formation of the infective stage — sporozoites.
- Migration and accumulation of the formed sporozoites in the mosquito's salivary glands, from where they are transmitted to a new host during blood-sucking.
What is the difference in the periodicity of paroxysms between tertian and quartan malaria?
The difference lies in the duration of the erythrocytic schizogony cycle and the frequency of malaria paroxysms.
| Characteristic | Tertian malaria (Plasmodium vivax) | Quartan malaria (Plasmodium malariae) |
|---|---|---|
| Cycle duration | 48 hours | 72 hours |
| Frequency of paroxysms | Every other day | Every two days |
In tertian malaria, the period of normal temperature between attacks (apirexia) is 40–43 hours. In quartan malaria, the cycle is longer, so attacks develop less frequently — every third day.
Class and exam questions
Which method is considered the primary one for laboratory confirmation of the diagnosis?
The main method is microscopic examination of thick and thin blood smears stained with Romanowsky-Giemsa stain. Parasite density per 1 µL of blood must be quantified.
Which form of malaria causes the most severe complications?
Malaria caused by Plasmodium falciparum (malignant tertian malaria). It can lead to cerebral malaria, acute renal failure, and hepatic failure.
How does the complete blood count change in plasmodial infection?
The hemogram typically reveals leukopenia, neutropenia, relative lymphocytosis, as well as signs of hemolytic anemia (decreased hemoglobin levels and erythrocyte count).
What else to study on this topic
- Clinical presentation of a malaria paroxysm: chills, hot, and sweating stages
- Specific complications of falciparum malaria and emergency care algorithm
- Pathogenesis of nephrotic syndrome in Plasmodium malariae infection
- Differential diagnosis of malaria with leishmaniasis, sepsis, and brucellosis
- Principles of radical and suppressive therapy, parenteral administration of drugs
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