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
How can the zoonotic risk of ascarids be reduced?
Prevent environmental contamination- educate pet owners, regular worming, hygiene
Regular worming- modern macrocyclic lactones- selamectin, milbemycin, moxidectin, fenbandazole, pyrantel
What is the most common way in which dogs are infected by toxocara canis?
Transplancental transmission
L2 arrested in the muscles of the bitch are activated during pregnancy and migrate across the placenta to the lungs then liver of the foetus
As the puppies are born the L2 moults to L3- coughed up- and swallowed and matures in 3 weeks
