Ascarids of dogs + cats

Question 1

What are the different ascarids?

Answer 1

*Toxocara canis
*Toxocara cati
*Toxascaris leonina

Question 2

What does Toxocara canis affect? Zoonotic?

Answer 2

Dogs + Foxes
Zoonotic!

Question 3

What does Toxocara cati affect? Zoonotic?

Answer 3

Cats
Zoonotic?

Question 4

What does Toxascaris leonina affect? Zoonotic?

Answer 4

Cats + Dogs
Not Zoonotic

Question 5

What are common characteristics of ascarid nematodes?

Answer 5

• Large, white, fleshy worms
• Direct life cycles
• May include paratenic host
• Infective stage = egg containing the L2
• Eggs highly resistant
• Infections usually stimulate strong immunity

Question 6

What are paratenic hosts? definition

Answer 6

not essential to life cycle but some
development may occur
(Intermediate host = essential)

Question 7

What is the morphology of adult worms?

Answer 7

• Large, white, fleshy worms
• Found in small intestine
• Females produced ~ 200,000 eggs/per day
• Strong, effective immune response

Question 8

What is the morphology of Toxocara spp eggs?

Answer 8

• 80 μm
• Spherical
• Thick-shelled, brownish in colour
• Morula fills the egg

Question 9

What is the morphology of Toxascaris leonina eggs?

Answer 9

• 80 μm
• Oval
• Thick-shelled
• Morula doesn’t fill the egg

Question 10

What are the 4 routes of infection of Toxocara canis?

Answer 10

1.Direct transmission - Puppies <12wks
2.Paratenic Transmission
3.Transplancental transmission - >6m/o
4.Transmammary transmission

Question 11

Which ascarids have a large cervical aeli?

Answer 11

T. cati

Question 12

What does the male T. canis worms have at tail end?

Answer 12

fingerlike projection at tail end

Question 13

What is the direct transmission route of infection?

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); PPP ~6 weeks.

Question 14

What is the paratenic route of transmission?

Answer 14

• Paratenic host ingests eggs; Paratenic host ingested; Mucosal migration to gut; PPP 4 weeks

Question 15

What is the transplacental transmission route of infection?

Answer 15

• L2 migrates into tissues, becomes encysted and development is arrested.
• Pregnancy – reactivates L2, crosses the placenta to the foetal liver; PPP 3 weeks.

Question 16

What is the transmammary route of infection?

Answer 16

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

Question 17

What is the lifecycle / route of infections of Toxocara cati?

Answer 17

• Ingestion of eggs containing L2 – migration
• PPP 8 weeks
• Ingestion of paratenic host – no migration
• PPP 6 weeks
• Transmammary transmission – no migration
• PPP 2-3 weeks
• No transplacental transmission

Question 18

What is the life cycle / route of infection of Toxascaris leonina?

Answer 18

• Dogs and cats
• No migration
• Infection by ingestion of
• Egg containing L2
• Paratenic host
• No transplacental transmission
• No transmammary transmission

Question 19

What are the clinical signs in adult dogs?

Answer 19

ASYMPTOMATIC

Question 20

What are the clinical signs in puppies?

Answer 20

• Heavy worm burdens in puppies
• Pot bellied
• Poor weight gain
• Intestinal obstruction
• Pneumonia associated with pulmonary phase
• No diarrhoea

Question 21

How is ascarids diagnosed?

Answer 21

• Age of dog/cat
• Clinical signs
• Eggs in faeces (salt flotation often not necessary)
• Adult worms may be passed or vomited

Question 22

How is ascarids controlled?

Answer 22

• Intestinal stages susceptible to benzimidazoles and macrocyclic lactones
• Dogs: Fenbendazole given daily from 42 days gestation can prevent transplacental transmission
• Cats: Emodepside ~7 days before expected parturition to prevent lactogenic transmission.
• Regular worming – 2, 4, 6 weeks of age; 3, 6 months and then every 3-6 months.
• Cats – no transplacental transmission, can start treatment at 3 weeks of age

Question 23

How do you reduce the zoonotic risk of ascarids?

Answer 23

• Eggs are highly resistant and long lived
• 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)

Question 24

Describe the migration of L2 ascarid larvae in the cat and dog host.

Answer 24

Hepato-tracheal migration, where the L2 hatches from the egg in the gut of the dog/cat, pentetrates though the wall of the small intestine and migrates to the liver and is carried to the lungs in the blood stream. The L2 moults to the L3 and is coughed up and swallowed, maturing to the L4 the L5/adult worm in the small intestine.

Question 25

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

Answer 25

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.

Question 26

How do differentiate between T. canis, T. cati and T. leonina adult worms?

Answer 26

Male Toxocara spp. worms have a small appendage on its posterior end which is absent in T. leonina worms. T. cati has an inflated cervical alae, it is sometimes referred to the arrow-head worm.

Question 27

What treatment is used to control ascarids in dogs and cats?

Answer 27

Benzimidazoles
Macrocyclic lactones