Zoonotic Nematodes

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Zoonotic Nematodes:

Toxocara canis - found in GI tract of dogs, ocular disease in man

Toxocara canis life cycle:

Routes of infection:

oral (direct) - L3 in egg

Transplacental

Transmammary

Paratenic host

Outcome of infection (in dog):

depends on age of animal

< 3 months - liver/lung migration and development to adults in SI

> 3 months - larvae migrate to tissues

*larvae can't arrest in the tissues of older animals and become re-activated during pregnancy (through placenta to developing pups in utero)

Humans become a dead end paratenic host as not predated (accidental ingestion of eggs, hatch in GI tract, larvae migrate to tissues and cause disease)

T.canis: arrested larval development

arrested L3 hypobiotic - resistant to anthelmintics

survive for the life of the bitch

arrested L3 can re-commence development in the bitch (infect all subsequent litters)

Controlled by host immune and/or hormonal status

*Transplacental transmission ensures 100% infection

*L3 in milk for up to 5 weeks (transmammary transmission) - second wave of infection, 5 weeks after birth of pup

Prevalence very high in young animals

Parasites in dogs can infect fox and vice versa - reservoir of infection for dogs = foxes never treated with anthelmintics

Environmental contamination:

females prolific egg layers

unembryonated egg is not infected (must larvate + grow molts)

Eggs sticky and resistant

Infective egg contain L3 that cause infection

very hard to remove from environment

Human infection:

- can remain active for many months, if not year

- preference to move to liver and eyes

Ingesting a couple of eggs - elicit an antibody response but may not result in any pathology (can end up in eye and cause disease as not recognised by body - can cause blindness)

children who have a habit of ingesting soil - larger larvae uptake, high burden of infection

Toxocara cati:

no transplacental infection

transmammary most important for kittens

direct route - migration

persists due to ability to arrest and hide from currently available drugs

cats are more fastidious in toilet habits (burry faeces) - restricts human ifection

Difficult to ID between cat or dog strain - strong cross reactivity

Baylisascaris procyonis:

don't have raccoons in UK

emerging zoonotic parasite in America

Racoon becoming more urbanised so increase in contact with humans and dogs (racoon poo)

Rodents and rabbits will take up larvated egg and will develop and move and accumulate in brain = affect behaviour and increase chance of predation and transmission back to raccoon

half of human infected will die or change behaviour as in brain

Anisakis simplex:

Dolphins and whales definitive hosts = found in oceans

Shed eggs into sea and infect intermediate hosts (shrimps etc)

predated by fish (3rd larval stage)

Sushi and improperly cooked fish cause transmission to humans

if gut fish = no problem but if take too long to gut - larvae will move into muscles

Trichinella spiralis = infection of pigs