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What causes ascariasis?
Medical expert of the article
Last reviewed: 06.07.2025
Cause of ascariasis
Ascaris is a large, spindle-shaped, pale pink worm. The female is 25-40 cm long, the rear end of the body is straight and pointed, the male is 15-20 cm long, the tail end is hooked onto the ventral side. The body of the helminth is covered with a thick, transversely striated cuticle. The female lays more than 200 thousand fertilized and unfertilized eggs per day in the intestinal lumen. The eggs are excreted with feces into the environment. The lifespan of an ascaris is about 1 year.
Pathogenesis of ascariasis
The invasive roundworm larva is released from the membranes under the influence of enzymes of the upper gastrointestinal tract. In the small intestine, the larva penetrates the epithelial lining into the blood vessels with the help of peptidase and hyaluronidase enzymes. The introduction of larvae is facilitated by the activation of endogenous inflammatory factors by their metabolites. Through the portal vein system, the larvae migrate through the liver to the right side of the heart, and through the pulmonary circulation enter the lungs. From the capillaries, they actively penetrate the alveoli, then gradually rise along the bronchial tree to the larynx, enter the pharynx, are swallowed with saliva and again enter the small intestine. The migration process takes 2-3 weeks. In the small intestine, mainly in the ileum, the larvae mature into adults, which takes about 2 months.
Metabolites of larvae and products released during their molting have high immunogenicity. During migration and in the small intestine hyperemia, edema, proliferation of lymphoid, macrophage elements, eosinophilic local and general reaction occur. Depending on the intensity of invasion, the early stage of the disease can be subclinical or manifest itself as a pronounced general allergic reaction, and in case of massive invasions in children - severe organ damage. In addition to the inflammatory reaction with hypersecretion of intestinal enzymes - enterokinase, alkaline phosphatase, digestive disorders in ascariasis are facilitated by a violation of the production and mutual regulation of peptide hormones (gastrin, secretin). In children, absorption of fats, proteins is impaired, lactase deficiency, vitamin A and C deficiency develop. Ascaris are capable of secreting immunosuppressive substances, which is manifested by a decrease in the effect of vaccination.