Epidemiology and routes of transmission
For most roundworms, the standard rule applies: the parasite's eggs must first mature in the soil. In this case, humans are infected alimentarily by consuming contaminated water or food.
However, there are important exceptions:
- Enterobiasis: transmitted by contact and household means; the stage of maturation in the soil is absent.
- Trichinellosis: the parasite does not enter the external environment; its life cycle constantly proceeds inside the organisms of animals or humans.
Enterobiasis: features of infestation
The causative agent is the pinworm (Enterobius vermicularis), a small nematode ranging from 2 to 12 mm in size. The infection is transmitted from an infected person and is characterized by high contagiousness (morbidity exceeds 1,000 cases per 100,000 population). 90% of those infected are children from organized groups.
Life cycle within the host:
- From swallowed infective eggs, larvae hatch in the small intestine.
- They migrate to the cecum, reaching sexual maturity.
- Fertilized females passively descend with feces into the rectum.
- At night, the females actively crawl out of the anus, lay eggs in the perianal folds, and die.
Clinical presentation: A pathognomonic symptom is pronounced nocturnal pruritus in the perianal region (in girls, it can spread to the vulva). Spastic abdominal pain, diarrhea, and persistent insomnia are also characteristic. Scratching the skin leads to autoinfection (eggs are deposited under the fingernails and back into the mouth), as well as local complications: pyoderma, eczema, vulvovaginitis.
Diagnostics: visual detection of pinworms or the gold standard — microscopy of a perianal swab (regular stool analysis has low diagnostic value).
Ascariasis: clinical phases
The causative agent is the large human roundworm (Ascaris lumbricoides). The disease proceeds with pronounced stages.
1. Larval migration phase (first 1–2 weeks) Larvae penetrate the intestinal wall and are carried by the bloodstream to the lungs, where they spend 8–10 days. This causes intoxication, rash, cough, shortness of breath, and wheezing. Laboratory findings reveal hypereosinophilia (up to 80%) and specific antibodies, while chest X-rays show transient ("fleeting") eosinophilic infiltrates.
2. Intestinal phase (chronic) Larvae are coughed up, swallowed with saliva, and enter the small intestine, where they grow into giant worms (20–35 cm) over 8–10 weeks. Pain in the mesogastrium, nausea, sialorrhea, and asthenia occur. Due to the large size of the helminths, surgical complications are possible: acute intestinal obstruction, appendicitis, cholangitis. Diagnostics: coproovoscopy (stool analysis), but eggs can be detected no earlier than 10–11 weeks after infection.
Principles of treatment and prevention
The basis of treatment is etiotropic drugs (pyrantel, mebendazole, albendazole). At the same time, pyrantel for enterobiasis is prescribed at a dose of 10 mg/kg twice with an interval of 1–3 weeks to destroy individuals that have hatched after the first dose.
The basic element of prevention for all nematode infections is strict adherence to hygiene. When treating enterobiasis, it is critically important to trim fingernails short for 3 days, take a shower, and iron underwear with a hot iron daily.
Criteria for cure:
- Enterobiasis: negative perianal swab 6–7 days after therapy.
- Ascariasis: triple stool analysis with intervals of 2 weeks (starting from 10–14 days after treatment).
Remember the exceptions to the soil maturation rule: ET (Enterobiasis — no soil, Trichinellosis — no external environment).
Class and exam questions
Why is stool analysis for helminth eggs ineffective in enterobiasis?
Female pinworms do not lay eggs in the intestinal lumen. They do this outside, in the perianal folds, which is why a scraping or adhesive tape method is needed for diagnosis.
What is the danger of skin scratching in enterobiasis?
In addition to the risk of acquiring a bacterial infection (pyoderma), scratching contributes to the accumulation of eggs under the fingernails, their transfer to the mouth, and continuous self-infection (autoinfection).
What happens in the lungs during ascariasis?
Ascarid larvae enter the lesser circulation via the bloodstream and stay in the lungs for 8–10 days, causing bronchopulmonary syndrome and the formation of "fleeting" eosinophilic infiltrates.
What else to study on this topic
- Mechanisms of formation of transient Löffler infiltrates in the lungs
- Differential diagnosis of bronchopulmonary syndrome in helminth infections
- Specifics of sanitary and epidemiological control in kindergartens
- Complications of the intestinal phase of ascariasis: pathogenesis of mechanical obstruction
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