PARASITES AND PARASITIC DISEASES OF DOMESTIC ANIMALS


The Nematodes

Paralephostrongylus tenuis - life cycle

The predilection site for this nematode is the brain (A) of white-tailed deer, specifically the subdural space and meningeal venous sinuses.

Pre-parasitic phase

The pre-parasitic phase of larval development takes place entirely inside an intermediate host. Development of fre-living stages does not does not occur in this life cycle.

The location of adults in the brain means that eggs and hatched first stage larvae must undergo a tortuous path through the body of a host in order to reach the external environment where they will encounter  required intermediate hosts.

-----> Migration route of eggs and first stage larvae(L1s) from the brain to the external environment.

Eggs are deposited in the venous sinuses by female worms. These eggs are carried via venous blood flow to the right heart (B) and then via the pulmonary arteries to the lungs(C) where they lodge in the alveolar capillary beds. First stage larvae(L1s) develop, hatch, escape into the alveoli and migrate up the bronchial tree(D) - aided by the upward flow of epithelial cilia - to the pharynx where they are swallowed. They pass through the gastrointestinal tract and out to the external environment with the hosts feces.(E)

Terrestrial gastropods (slugs and snails) serve as intermediate hosts. They are infected when L1s penetrate the gastropod foot, as the snails and slugs travel across deer feces. The infective third larval stage (L3) is reached in gastropods following two molts (L1 to L2 to L3).

Parasitic phase

-----> Migration route of ingested L3s to the brain.

Deer are infected by ingesting (F)  infected slugs and snails as they browse and graze on low vegetation. Third-stage larvae are released from snail and slug tissues during digestion in the abomasum and small intestine. They penetrate the gut wall, migrate across the peritoneal cavity to the lumbar vertebrae, follow the lumbar nerves, and reach the vertebral canal approximately ten days after infection. Growing, developing larvae migrate anteriorly in the neural parenchyma, specifically the dorsal horns of the gray matter. Approximately forty days after infection, immature adults can be found in the subdural space of the spinal cord in which they continue their migration to the predilection site - the subdural space and meningeal venous sinuses of the brain. Immature adult worms complete their development to sexual maturity, copulation takes place, and adult female worms complete the cycle by laying their eggs in the meningeal blood vessels.

The prepatent period is approximately 7weeks (range = 82-91 days).


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Parasites and parasitic diseases of domestic animals
Dr. Colin Johnstone (principal author)
Copyright 1998 - University of Pennsylvania
This page was last modified on February 11, 2000