Ascarids of Dogs and Cats Flashcards
What are the common characteristics of ascarid nematodes?
Large, white, fleshy worms
Direct life cycles- may include paratenic
Infective stage = egg containing L2
Infections usually stimulate strong immunity
What is the difference between a paratenic and intermidiate host?
Paratenic- not essential to life cycle but some development may occur
Intermediate host- essential to life cycle
What are the three ascarids of cats and dogs?
What species do they affect and are they zoonotic?
Toxocara canis- dogs and foxes- zoonotic
Tocoara cati- cats- zoonotic?
Toxocaris leonina- cats and dogs, not zoonotic
What is the morphology of adult ascarids?
Large, white, fleshy worms
Found in the small intestine
Females produced 200,000 eggs/day
How can Toxocara canis and Toxascaria leonina be distinguished from a Toxocaris cati?
On the head of T.canis/T.leonina there is a small alae
On the head T. cati there is a large arrow shaped alae
How can Toxocara and Toxascaris be distinguished?
On the tail of male Toxocara spp there is a finger like projection that toxascaris lacks
Describe the morphology of toxocara spp eggs
80um
Spherical
Thick-shelled, brown-ish
What species is are these eggs from?
Toxascaris leonina
80um
Oval
Thick-shelled
Morula doesn’t fill the egg
What are the 4 routes of transmission for Toxocara canis?
Direct transmission- egg containing infective larvae L2/L3 ingested, hepato-tracheal/pulmonary migration
Paratenic transmission- paratenic host ingested, mucosal migration to gut
Transplancental transmission- L2 migrates into tissues, becomes encysted and development arrested until pregnancy- L2 crosses the placenta to foetal liver
Transmammary transmission- L2 in milk, no migration- larvae develop into adults in intestine
What is the pre-patent period of each route of infection for toxocara canis and who is susceptible?
Direct- Puppies <12 weeks- PPP- 6 weeks
Paratenic- PPP- 4 weeks
Transplancental > 6 months old- PPP- 3 weeks
Describe the different life cylces of Toxocara cati and their associated pre-patent period
Ingestion of eggs containing L2- migration
PPP- 8 weeks
Ingestion of paratenic host- no migratoin
PPP- 6 weeks
Transmammary transmission- no migration
PPP- 2-3 weeks
Describe the life cycle of the Toxasacris leonina
Dogs and Cats
No migration
Infection by ingestion of egg containing L2/paratenic host
What disease symptoms are caused by infection of ascarids?
Asymptomatic in adult dogs
Heavy worm burdens in puppies-
Pot bellied
Poor weight gain
Intestinal obstruction
Pneumonia associated with pulmonary phase
No diarrhoea
How are ascarids diagnosed and controlled?
Diagnosis
- Age of dog and cat
- Clinical signs
- Eggs in faeces- salt flotation often not necessary
- Adult worms passed or vomited
Control
- Intestinal stages susceptible to benzimidazoles and macrocyclic lactones
- Dogs- fenbendazole given daily from 42 days of gestation can prevent transplancental transmission
- Cats- emodepside 7 days before expected parturition
- Regular worming- 2, 4, 6 weeks of age, 3,6 months then every 3,6months
- Cats- no transplancental so can start at 3 weeks
How are humans infected by Toxocara canis?
What are the different diseases caused?
Humans infected by ingesting eggs containing L2/3 larvae
L2 hatch and migrate
Visceral larva migrans- coughing, wheezing, pruritus
Ocular larva migrans- retinitis
Neurotoxocariasis- fever, encephalitis
Covery toxocariasis- asthma
