Ascarids (Ca & Fe)

Question 1

What are ascarids?

Answer 1

• NEMATODES
• family ascarididae (roundworms)

Question 2

What are the ascarids we care about?

Answer 2

1. Toxascaris leonina (Ca & Fe)
2. Toxocara canis (Ca)
3. Toxocara cati (Fe)
4. Baylisascaris spp. (Ca)

Question 3

Where are ascarids found?

Answer 3

stomach & small intestines

Question 4

Defining features of adult Toxascaris leonina?

Answer 4

• two long & narrow lateral cervical alae @ the anterior end
• males have no finger-like projection at the posterior end (unlike Toxocara canis)

Question 5

Defining features of Toxascaris leonina eggs?

Answer 5

• sub-spherical (“squash ball” appearance) w/ thick smooth shell
• each egg contains 1 or 2 cells when passed

Question 6

Hosts of Toxascaris leonina?

Answer 6

• Ca & Fe
• other canids & felids (as definitive hosts)
• other mammals & birds (as paratenic hosts where the parasite remains as larvae in tissues & does not complete its development to adults in the GI system)

Question 7

What is the geographic distribution of Toxascaris leonina?

Answer 7

• around the world
• in 3% of shelter Ca in national study, somewhat higher in Western Canada
• Not detected in shelter Fe in national study & @ low prevalence in owned & free roaming/rural cats in other studies in Western Canada

Question 8

What is the life cycle of Toxascaris leonina?

Answer 8

• adult nematodes live in the intestine of the canid or felid definitive host & produce eggs shed in feces
• larvae dev w/in eggshell to infective 3rd stage (L3) @ temp dep rate (generally 1-4 wks)
• infective third stage larvae w/in the eggs are ingested by Ca or Fe
• then larvae is released to undergo mucosal migration (GI tract lumen to mucosa to lumen) w/in GI system.
• 8-10 week prepatent period
• neither pre-natal nor trans-mammary transmission, nor somatic larvae
• life cycle may also involve, but does not require, sm mammal paratenic hosts, in which 3rd stage larvae are hatched from ingested eggs follow somatic migration (GI tract to portal vessels to liver to heart to lungs to heart to somatic tissues)
• 3rd larvae in tissues of paratenic host are infective for the Ca or Fe definitive hosts
• following ingestion by a Ca or Fe, these larvae too undergo a mucosal migration (8-10 wk PPP)

Question 9

What is the epidemiology of Toxascaris leonina?

Answer 9

• mjr route of transmission among Ca is probably through infective eggs & for Fe through infected paratenic hosts
• eggs are v resistant to adverse enviro conditions & can survive & remain infective for months or perhaps years
• eggs are not immediately infective, but require @ least a wk in enviro to become infective for DHs & paratenic hosts
• eggs can be inactivated by strong phenol, cresol, or bleach solns, high temps (> 45 C), & desiccation
• eggs are more freeze tolerant than those of Toxocara spp. & freezing @ -20 C will not reliably inactivate them
• eggs are not inactivated by most common disinfectants, nor by fixation in formalin or ethanol
• frequent occurrence in Ca in N. Canada suggests that parasite is well adapted to relatively cool & harsh enviro
• has been detected in Arctic fox well above the Arctic circle

Question 10

What is the pathology & clinical signs of Toxascaris leonina?

Answer 10

• larval & adult have effects in GI tract similar to those of Toxocara canis & are generally mild unless lrg # of parasites are present in young animals or in those that are otherwise compromised
• in Ca & Fe, it does not migrate beyond GI mucosa
• clinical signs seen in juveniles are often asymptomatic, pot belly, poor growth, staring coat, diarrhea, respiratory signs, seizures, & death (v rare)

Question 11

How is Toxascaris leonina diagnosed?

Answer 11

• usually vague clinical signs associated w/ it aren’t helpful
• adult parasites may be found in feces or vomit
• eggs may be detected on routine fecal float (relatively sensitive for ascarid eggs)
• newer coproAg & coproPCR methods are increasingly avail & useful in detection of ascarid infections (including PPP)

Question 12

Is Toxascaris leonina zoonotic?

Answer 12

no

Question 13

Defining features of adult Toxocara canis?

Answer 13

• two long & narrow lateral cervical alae
• 3 “lips” @ anterior end
• males have short finger-like projection @ posterior end

Question 14

Defining features of eggs of Toxocara canis?

Answer 14

• sub-spherical (“golf ball” appearance) w/ thick, rough shell
• each egg contains 1 or 2 cells when freshly passed