Introduction to Parasitology

Summary of important information about specific life cycles

Table 1 Toxocara canis Dirofilaria immitis Fasciola hepatica Haemonchus contortus
Route(s) of entry to the host 1. Ingestion of infective eggs
2. Ingestion of mouse hosts (paratenic)
3. Transplacental migration of L2s to fetal liver
4. Transmammary transmission of L3s to nursing pups
1. Injection of L3s by blood-feeding female mosquitos (intermediate hosts) 1. Ingestion of metacercariae 1. Ingestion of infective larvae
Predilection site Small intestine Right ventricle and pulmonary arteries Bile ducts of the liver Abomasum
Route to the predilection site Direct development in the small intestine after ingestion of paratenic hosts and L3s from the mammary gland. Otherwise by tracheal migration. Migration through the body and vascular system Migration from the small intestine across the peritoneal cavity to the liver Direct development in the abomasum after ingestion
Route of exit from the host In the feces of the host In the blood meal taken by a mosquito feeding on the host. In the feces of the host In the feces of the host
Life cycle stage(s) entering the host  Egg, L2 or L3 depending on the route of transmission L3 Encysted metacercaria Ensheathed L3
Stage leaving the host (diagnostic stage) Egg Microfilaria Egg Egg




Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on January 24, 2000