SA Ascarids

Question 1

Name the three main ascarids of SA and their primary hosts.

Which are considered zoonotic?

Answer 1

Toxocara canis, cati, Toxascaris leonia

Canis and cati are zoonotic

Question 2

Describe the morphology of Toxocara spp.

Answer 2

• Large, white, up to 10cm adults
• Inflated cuticle forms allae - more pronounced in cati
• Toxocara (xx toxascaris) have a cuticular protrusion

Question 3

Describe the morphological features of Toxocara eggs.

Answer 3

• Large, thick pitted shell
• Spherical
• Filled with dark brown undifferentiated morular

Question 4

Describe the morphological features of Toxascaris eggs.

Answer 4

• Oval
• Inside morular doesn’t fully fill the egg
• Difficult to differentiate in a mixed population

Question 5

What clinical signs are associated with Toxocara/ Toxascaris related disease?

Answer 5

• Asymptomatic in adults
• With heavy puppy burdens
  
  • Pot bellied
  • Poor wt gain
  • Intestinal/ bilary obstruction
  • No diarrhoea
• May show worm hypersensitivity - coughing

Question 6

How can Toxocara/ Toxascaris be diagnosed/ controlled in dogs?

Answer 6

1. Diagnosis - Clinical signs, signalment, salt flotation, adult worms passed in vom/faeces
2. Control -
   
   1. Intestinal stages - BZ/ML
   2. TPT - FBZ from 42 days gestation
   3. Regular worming
      
      1. 2,4,6, weeks of age
      2. 3,6 months
      3. Then every 3-6 months

Question 7

Outline the lifecycle and modes of transmission of Toxocara canis.

Describe the migratory pattern of Toxocara canis.

Answer 7

Transmission

• Ingestion of infective eggs containing L2 by dog
• TPT - Transplacental transmission - L2 cross placenta at d40 of gestation after being arrested in muscle
• TMT - Transmammary transmission - L2 enter puppies through L2 in milk

Hepatotracheal migration - L2 migrates from SI to liver to lungs. –> coughed up and swallowed - reproduce and eggs are shed in faeces

Question 8

What is the PP for toxocara in adult dogs?

How does this differ in puppies and why?

Answer 8

Adults: 4-6 weeks

Puppies: 3 weeks - L2 infect puppies (not eggs as in adults)

Question 9

Which stage of the Toxocara canis are infective?

Answer 9

Larvated egg stage

Question 10

Which human group is most at risk of Toxocara canis infection?

Answer 10

Children - kids similarly curious as dogs!

Question 11

How do the infection and incidence rates of Toxocariasis compare?

What clinical signs are associated with the disease

Answer 11

Infection rate is high but incidence rates of disease are low.

Aberant migration of larva to the eye (often retina), this may be misdiagnosed as a tumour. Hypersensitivity causes blindness

Question 12

How can occular toxocariasis disease be controlled/ prevented?

Answer 12

1. Prevent environmental contamination with eggs (very resistent once present)
   
   1. Educate pet owners - regular worming
   2. Hygiene - wash hands!

Question 13

Which anthelmintics are used in the control of Toxocara in dogs and cats?

Answer 13

1. ML - Selamectin, milbemycin, moxidectin
2. FBZ, PYR
3. Emodepside

Question 14

How does the lifecycle of Toxocara cati differ to Toxocara canis?

Answer 14

1. Ingestion of L2 eggs - migration
2. Ingestion of paratenic host - no migration
3. TMT - no migration
4. No TPT

Question 15

How does the Toxascaris leonina life cycle differ to Toxocara?

Answer 15

1. Infection occurs only by ingestion of L2 eggs and paratenic hosts
2. No TMT or TPT

Question 16

Answer 16

Alae folds of Toxocara canis - restricted on one side

Question 17

Answer 17

Alae of Toxocara cati - more pronounced than in canis

Question 18

Answer 18

Egg of Toxascaris leonina - egg is oval with the inside morula not completely filling the egg

Question 19

Answer 19

Toxocara egg - round, brown with thick pitted shell