IN ANIMALS
AETIOLOGY AND EPIDEMIOLOGY • Three species of roundworm are known to infest dogs and cats in Australia: T. canis (canine only),
T. cati (feline only) and Toxascaris leonina (canine and feline). Toxascaris leonina is not a known zoonosis. In addition to domestic dogs, T. canis occurs widely in wildlife (foxes and dingoes) in Australia. 2 • Companion animals can become infested through ingestion of embryonated eggs, consumption of paratenic hosts (such as snails, birds and rodents) or via transmammary transmission. 1 Transplacental transmission of larvae from the bitch to pups in-utero is also an important route of transmission for T. canis. • When infective eggs are ingested by adult dogs, roundworms commonly undergo arrested development. Larvae travel through the intestinal wall, undergo hepatopulmonary migration and are distributed throughout the body, including the liver, lungs, muscles and other organs, without completing their life cycle. Somatically arrested T. canis can reactivate in pregnant bitches and be transmitted to pups.
Embryonated (infectious) Toxocara canis egg
• Lactogenic transmission of T. cati only occurs after acute infection of the queen during late pregnancy. 3 Unlike T. canis, transmammary infection of kittens following reactivation of arrested somatic larvae in chronically infected queens does not play a strategic role in the life cycle of T. cati. • In younger dogs, tracheal, as opposed to hepatopulmonary migration predominates, so that most worms are coughed
v Life cycle of Toxocara canis
Life cycle of Toxocara canis
D.H. Dog
Adults (detail of the anterior end)
Prepatent period: Approximately 5 weeks aer egg ingestion
Late in pregnancy, encysted larvae (somatic larvae) in the dam are activated. These larvae migrate mainly to the uterus and into the puppies (transplacental infestation), and rarely, via the mammary glands. Thus puppies may be infested prior to, and shortly aer, birth
Faeces
P.H. (rodents)
In the P.H.: eggs hatch, L3 larvae migrate into tissue and encyst until P.H. ingested by a susceptible carnivore
Non-infective egg
Humans (especially children) can accidentally ingest infective eggs
D.H. = definitive host P.H. = paratenic host
Infective egg
Extracted from the Textbook of Clinical Parasitology in dogs and cats, Beugnet F., Halos L., Guillot J., Ed Servet, 2018. Life cycles adapted from Pet Owner Educational Atlas. Parasites, Carithers D. and Miro G., Ed Servet, 2012. Life cycle from Beugnet, F., et al (2018) Textbook of Clinical Parasitology in Dogs and Cat. Grupo Asis Biomedica, S.L.; Adapted from Carithers, D., et al (2012) Pet Owner Educational Atlas.
CONTENTS
Companion Animal Zoonoses Guidelines 84
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