GI nematodes: Toxocara canis

Question 1

Features of T. canis

Answer 1

1. Eggs have thick, pitted shell
2. Infective stage larvae are sm (200 microns)
3. Adults are large (20cm)

Question 2

What are the 4 routes of infection?

Answer 2

1. Direct - oral
2. Transplacental
3. Transmammary
4. Via parenteric host (not true intermediate host)

Question 3

What does the outcome of infection depend on?

Answer 3

The age and immune status of the animal

• < 3 months old, migrate to liver then lung and then developinto adults in the SI
• > 3 months olds, larvae migrate to tissues

Question 4

Describe the life cycle of T. canis in dog < 3 months old

Answer 4

1. Egg containing L3 stage is ingested by dog
2. L3 hatches in SI and migrates via liver to lungs
3. L3 migrates to SI via trachea
4. L3-L4, adult develops in SI
5. Adults in SI release eggs that excreted into environment in faeces

Question 5

What type of migration do the larvae show?

Answer 5

Heptatracheal migration

Question 6

Describe the lifecyle in bitches < 3 months, giving rise to transplacental migration

Answer 6

1. L3 in egg is ingested
2. L3 hatches in SI
3. L3 migrates to tissues and arrests
4. L3 activated about 3 weeks pre-partum
5. L3 migrates from bitches tissue to foetal lung
6. L3 migrates to the SI via trachea
7. L3 develops into L4, adult form found in SI
8. 2 weeks after birth puppy will have patent infection and will shed eggs in faeces

Question 7

Give 5 features of arrested larval development

Answer 7

1. Arrested L3 form is hypobiotic (resistant to commonly used anthelmintics)
2. Can survive in tissues for whole of bitches life
3. Can be reactivated when immunity is lowered during pregnancy
4. Reactivation could be due to hormonal influence

Question 8

What feature of female worms makes T. canis highly infectious?

Answer 8

Very fecund (highly fertile) and can produce thousands of eggs per day.

Question 9

State clinical signs seen during the migratory phase

Answer 9

1. Coughing
2. Increased respiratory rate
3. Pneumonia in heavy infections

Question 10

State clinical signs seen during the enteral phase

Answer 10

1. Pot bellied puppies

2. Reduced growth rates in puppies

Question 11

What are treament options for T. canis?

Answer 11

1. Anthelmintics to prevent environmental contamination