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What causes ascariasis?
Last reviewed: 20.11.2021
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The cause of ascaridosis
Ascaris - a large worm spindle-shaped, pale pink. The female is 25-40 cm long, the posterior end of the body is straight, pointed, the male is 15-20 cm long, the caudal end hooks on the abdominal side. The body of the helminth is covered with a thick cross-striated cuticle. Female lays in the lumen of the intestine more than 200 thousand fertilized and unfertilized eggs per day. Eggs are excreted with feces into the environment. Life expectancy of the roundworm is about 1 year.
Pathogenesis of ascariasis
The invasive larva of the roundworm is released from the membranes when exposed to the enzymes of the upper gastrointestinal tract. In the small intestine, the larva penetrates through the epithelial cover into the blood vessels with the help of enzymes peptidase and hyaluronidase. The introduction of larvae is facilitated by their activation by metabolites of endogenous factors of inflammation. According to the portal vein system, larvae migrate through the liver to the right side of the heart, enter the lungs through a small circle of circulation. From the capillaries they actively penetrate into the alveoli, then gradually along the bronchial tree they rise to the larynx, fall into the pharynx, swallow with saliva and again enter the small intestine. The migration process takes 2-3 weeks. In the small intestine, mainly in the iliac, larvae mature to adult individuals, which takes about 2 months.
Metabolites of larvae and released in the process of their molting products have high immunogenicity. In the course of migration and in the small intestine, there are hyperemia, edema, proliferation of lymphoid, macrophagal elements, eosinophilic local and general reaction. Depending on the intensity of the invasion, the early stage of the disease may be subclinical or manifest as a pronounced general allergic reaction, and in cases of massive invasions in children - severe organ damage. In addition to the inflammatory reaction with hypersecretion of intestinal enzymes - enterokinase, alkaline phosphatase, digestion disorders in ascariasis is promoted by product disruption and mutual regulation of peptide hormones (gastrin, secretin). In children, the absorption of fats and proteins is impaired, lactase deficiency, deficiency of vitamins A and C develop. Ascarids are able to release immunosuppressive substances, which is manifested by a decrease in the effect of vaccination.