This species transmits the nematophagous fungal symbionts, Pochonia chlamydosporia and Paecilomyces lilacinus and control of these fungi affects survival and reproductive performance of the nematode in vitro.
Infections in humans is via direct transmission from dogs without the involvement of vectors or intermediate hosts. Eggs are present in dog hair, which are easily ingested by humans following close contact, grooming, petting, etc. In humans, Toxocara infections cause allergies, asthma, fetal mutagenesis, ocular toxocariasis and neurotoxocariasis.
The life cycle involves ingestion of eggs in soil or encysted larvae in prey or a paratenic host. Eggs are proteolytically activated in the dog stomach and infective larvae (L3) migrate into the mesenteric and portal veins, reach the liver, and then pass to the lungs. Here they may disseminate via the circulation to other organs such as the eye, brain, kidneys, where they encyst as arrested infective larvae, or penetrate the bronchioles, trachea, and pharynx and are swallowed and develop into adults in the small intestine.
During the last trimester of pregnancy, recrudescence of encysted larvae may occur, resulting in transplacental transmission to unborn pups and shedding of larvae in milk.
Species which are pathogenic to dogs include:
- Toxocara canis
- Toxocara cati
Heavy prenatal infections can cause severe abdominal discomfort, anemia and death in young puppies. Infected puppies often present at 4 - 6 weeks of age with pot-bellied, anemic and poor weight gain despite good appetite. In adult and young dogs, other symptoms, related to visceral migration include endophthalmitis, meningitis and pneumonia.
Diagnosis is usually based on the presence of eggs in feces, but larvae can be visualized from necropsy samples. Coprophagy, which is not unusual in dogs, may amplify the clinical relevance of coprological studies. ELISA and PCR assays are also available to help differentiate from other visceral larvae.
A differential diagnosis of causes of coughing would include the lungworm Aelurostrongylus abstrusus and Angiostrongylus vasorum. With perinatal mortality in puppies, canine herpesvirus would be a consideration.
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