Dog and Cat GI Nematodes- Toxocara spp. Flashcards
Nematodes of small animals
Superfamily Ascaridoidea Genus Toxocara
Species of Toxocara and their hosts
T. canis- host=dog/fox
T. cati- host=cat
(T. vitulorum)- host=cattle
Toxascaris leonina- host=dog/cat
T. canis- routes of infection
Direct life cycle with 4 possible routes of infection
- oral (direct)- L3 enclosed within the egg
- transplacental- most important route, very effective
- transmammary- back-up route to transplacental
- paratenic host- more important in t. cati d/t mouse/rodent as paretenic host
Outcome of T. canis infection
Outcome depends on the age of the animal.
if animal is younger than 3 months, adult worms develop in SI
If animal is older than 3-6 months, larvae tend to arrest in the tissues
T. canis infection in animals less than 3 months of age
Results in a patent infection- produces eggs.
Adults in the SI release eggs. Egg matures in environment and egg containing the L3 is ingested. L3 hatches in the SI and migrates via hepatotracheal migration (this extendsPPP and is also when we might see clinical signs in young animal). L3 goes to SI via trachea- in lungs, coughed and swallowed. L3 moults to L4 and L4 moults to adult in the small intestine. Adult in the SI releases eggs. Eggs are present as a source of infection in the environment for a very long time.
T. canis infection in older bitches- i.e. giving rise to transplacental infection
Bitch ingests L3, L3 hatches in the SI and L3 migrates into the tissue. In the tissues, it arrests and goes into a hypobiotic state. 3 weeks pre-partum, L3 re-acticates likely due to decreased immunity in the pregnant bitch, also some hormal influence. In the pup, the L3 migrates to the fetal lung. At birth, L3 goes to SI via trachea, L3-L4-adult in the SI.
PPP of T. canis
16 days to 21 days. Should be treating for worms at ~2 weeks of age.
T. canis: transplacental transmission
L3 reactivated 3 weeks pre-partum
Migrates to fetal lung. L3 travels to SI via trachea. Ensures 100% infection. Arrested larvae in tissues can’t be diagnosed.
T. canis: mammary transmission
L3 in the milk for up to 5 weeks
no migratory phase via this route of infection i.e. L3s go straight to the SI (not to the lungs)
T. canis- ALD and ALD+pregnancy
Arrested L3 is hypobiotic- resistant to commonly used anthelmintics. Survive fo the life of the bitch. Arrested L3 can re-activate (when immunocompromised).
ALD is a means of avoiding host IR in older animals.
In pregnant animals, when immunity is lower, L3s can become reactivated
Paratenic hosts of toxocara
L3 arrest in tissues of bird/rodent. No migration following infection of the dog.
Bird/rodent ingests eggs–> L3 arrest in tissues–> no development in paratenic host.
PPP = 3 weeks
paratenic hosts more important in T. cati
Important features of T. canis epidemiology
100% of pups infected via transplacental route.
Transmammary transmission for ~5 weeks
highest level of infection in pups less than 6 months old
GI infection in pup is temporary. Most worms expelled by 6-8 months old
Arrested L3 is very reisstant- 12-20% of adult dogs can be producing eggs in feces.
T. canis egg
Females produce 1000s of eggs/day
Unemvryonated egg is not infective, ~4 weeks to reach infectivity
eggs and are sticky and resistant- can stick to fingers or dogs’ coat etc.
Survive for ~14 months in 2% formalin
Ball of cells need to larvate and moult from L1–> L3- temperature dependent process
egg is the reservoir of infection in the environment
T. canis persistence in dog population
persists due to the variety of different routes of transmission. tissue migration gives rise to the transplacental and trans-mammary routes. Paratenic hosts can spread infection. resistance of eggs in environment.
Clinical signs of T. canis
- migratory phase: coughing, increased resp. rate, pneumonia in v. heavy infections
- enteral phase: pot-bellied pups, failure to thrive
