Ascarids of dogs and cats

Question 1

What are some common characteristics of ascarid nematodes?

Answer 1

• Large, white, fleshy worms
• Direct life cycles
• Eggs highly resistant due to thick egg shell
• Infections stimulate strong immunity

Question 2

Name the ascarid that affects dogs and foxes

Answer 2

Toxocara canis

Question 3

Name the ascarid that affects cats

Answer 3

Toxocara cati

Question 4

Name the ascarid that affects cats and dogs

Answer 4

Toxascaris leonina

Question 5

Which ascarid is zoonotic?

Answer 5

Toxocara canis

Question 6

Describe the morphology of adult ascarid nematodes

Answer 6

• Large, white, fleshy worms
• Can be up to 10cm in size
• Females are larger than males
• Females produce ~ 200,000 eggs/per day

Question 7

Where are adult worms found?

Answer 7

In the small intestine

Question 8

How can Toxocara cati be distinguished from Toxocara canis/Toxascaris at the head end?

Answer 8

T.cati has large obvious extensions of the cuticle (alae) which have an arrowhead appearance

Question 9

How can Toxocara and Toxascaris be distinguished?

Answer 9

The only way is if you have male Toxocara worms, because the tail end has a finger-like projection

Question 10

Describe the morphology of Toxocara spp eggs

Answer 10

• 80um
• Spherical
• Thick shelled
• Brown colour
• Morula fills the egg
• L2 or L3 inside the egg

Question 11

Describe the morphology of Toxascaris spp eggs

Answer 11

• 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

Question 12

What are the 4 routes of infection of Toxocara canis?

Answer 12

• Direct: puppies less than 12 weeks
• Paratenic transmission
• Transplacental transmission
• Transmammary

Question 13

Describe direct transmission of Toxocara canis

Answer 13

• 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)

Question 14

What is the PPP of direct transmission of Toxocara canis?

Answer 14

6 weeks

Question 15

Describe paratenic transmission of Toxocara canis

Answer 15

Paratenic host ingests eggs; Paratenic host ingested by a dog; Mucosal migration to gut where they stay and continue their development

Question 16

What is the PPP of paratenic transmission of Toxocara canis?

Answer 16

4 weeks (shorter as there isn’t extensive migration)

Question 17

Describe transplacental transmission of Toxocara canis

Answer 17

• 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

Question 18

What is the PPP of transplacental transmission of Toxocara canis?

Answer 18

3 weeks

Question 19

Describe transmammary transmission of Toxocara canis

Answer 19

L2 in milk; No migration – larvae develop into adults in intestine

Question 20

Which of the 4 lifecycles for Toxocara canis does not occur for Toxocara cati?

Answer 20

Transplacental transmission

Question 21

Describe the life cycle of Toxascaris leonina

Answer 21

• Dogs and cats
• no migration
• infection by ingesting an egg containing L2 or ingesting a paratenic host
• No transplacental or transmammary transmission

Question 22

What are the signs of ascarid disease in puppies?

Asymptomatic in adults

Answer 22

• Pot bellied
• Poor weight gain
• Intestinal obstruction
• Pneumonia associated with pulmonary phase

Question 23

How is ascarid infection diagnosed?

Answer 23

• 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

Question 24

How is ascarid infection controlled in dogs?

Answer 24

Fenbendazole given daily from 42 days gestation can prevent transplacental transmission

Question 25

How is ascarid infection controlled in cats?

Answer 25

Emodepside ~7 days before expected parturition to prevent lactogenic transmission

Question 26

How else can ascarid infection be controlled?

Answer 26

• 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

Question 27

How can the zoonotic risk of Ascarids be reduced?

Answer 27

1. Prevent environmental contamination:
   - Educate pet owners, regular worming of pets
   - Hygiene (hand washing)
2. Regular worming:
   - Modern macrocyclic lactones: Selamectin, milbemycin, moxidectin
   - Fenbendazole, Pyrantel
   - Emodepside (cats)

Question 28

Describe the most common way in which dogs are infected with Toxocara canis?

Answer 28

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.