Ascarids of dogs and cats Flashcards
What are some common characteristics of ascarid nematodes?
- Large, white, fleshy worms
- Direct life cycles
- Eggs highly resistant due to thick egg shell
- Infections stimulate strong immunity
Name the ascarid that affects dogs and foxes
Toxocara canis
Name the ascarid that affects cats
Toxocara cati
Name the ascarid that affects cats and dogs
Toxascaris leonina
Which ascarid is zoonotic?
Toxocara canis
Describe the morphology of adult ascarid nematodes
- Large, white, fleshy worms
- Can be up to 10cm in size
- Females are larger than males
- Females produce ~ 200,000 eggs/per day
Where are adult worms found?
In the small intestine
How can Toxocara cati be distinguished from Toxocara canis/Toxascaris at the head end?
T.cati has large obvious extensions of the cuticle (alae) which have an arrowhead appearance
How can Toxocara and Toxascaris be distinguished?
The only way is if you have male Toxocara worms, because the tail end has a finger-like projection
Describe the morphology of Toxocara spp eggs
- 80um
- Spherical
- Thick shelled
- Brown colour
- Morula fills the egg
- L2 or L3 inside the egg
Describe the morphology of Toxascaris spp eggs
- 80um
- Oval
- Thick shelled
- Morula doesn’t fill the egg
- Larvae can’t get out of the egg due to the thick egg shell so its all ingested
What are the 4 routes of infection of Toxocara canis?
- Direct: puppies less than 12 weeks
- Paratenic transmission
- Transplacental transmission
- Transmammary
Describe direct transmission of Toxocara canis
- Egg containing infective larvae (L2/L3) ingested
- Hepato-tracheal/ pulmonary migration – larvae migrate via liver to lungs, coughed up and swallowed, larvae develop through L4 – L5 (adult)
What is the PPP of direct transmission of Toxocara canis?
6 weeks
Describe paratenic transmission of Toxocara canis
Paratenic host ingests eggs; Paratenic host ingested by a dog; Mucosal migration to gut where they stay and continue their development
What is the PPP of paratenic transmission of Toxocara canis?
4 weeks (shorter as there isn’t extensive migration)
Describe transplacental transmission of Toxocara canis
- L2 migrates into tissues, becomes encysted and development is arrested
- Pregnancy reactivates L2, crosses the placenta to the foetal liver
- Can get 3 week old puppies with adult worms already in their gut
What is the PPP of transplacental transmission of Toxocara canis?
3 weeks
Describe transmammary transmission of Toxocara canis
L2 in milk; No migration – larvae develop into adults in intestine
Which of the 4 lifecycles for Toxocara canis does not occur for Toxocara cati?
Transplacental transmission
Describe the life cycle of Toxascaris leonina
- Dogs and cats
- no migration
- infection by ingesting an egg containing L2 or ingesting a paratenic host
- No transplacental or transmammary transmission
What are the signs of ascarid disease in puppies?
Asymptomatic in adults
- Pot bellied
- Poor weight gain
- Intestinal obstruction
- Pneumonia associated with pulmonary phase
How is ascarid infection diagnosed?
- Age of dog/cat (more likely in young animals)
- Clinical signs
- Eggs in faeces (salt flotation often not necessary)
- Adult worms may be passed or vomited
How is ascarid infection controlled in dogs?
Fenbendazole given daily from 42 days gestation can prevent transplacental transmission
How is ascarid infection controlled in cats?
Emodepside ~7 days before expected parturition to prevent lactogenic transmission
How else can ascarid infection be controlled?
- Intestinal stages susceptible to benzimidazoles and macrocyclic lactones
- Regular worming – 2, 4, 6 weeks of age; 3, 6 months and then every 3-6 months
How can the zoonotic risk of Ascarids be reduced?
- Prevent environmental contamination:
- Educate pet owners, regular worming of pets
- Hygiene (hand washing) - Regular worming:
- Modern macrocyclic lactones: Selamectin, milbemycin, moxidectin
- Fenbendazole, Pyrantel
- Emodepside (cats)
Describe the most common way in which dogs are infected with Toxocara canis?
Via transplancental transmission.
L2, arrested in the muscles of the bitch, are activated during pregnancy and migrate across the placenta to the lungs of the foetus. As the puppies are born, the L2 moults to the L3, is coughed up, swallowed and matures to the adult worm in about three weeks.
