Nematode Zoonoses - VISCERAL LARVAL MIGRANS

(Toxocariasis)

AGENT:

Most cases of visceral larval migrans (VLM) are due to Toxocara canis, an ascarid of dogs and other canids, but in a few cases Toxocara cati in domestic cats has been implicated and rarely Baylisascaris procyonis of raccoons.

RESERVOIR AND INCIDENCE:

The reservoir mechanism for T. canis is latent infections in female dogs which are reactivated during pregnancy. Transmission from mother to puppies is via the placenta and milk. The life cycle of T. cati is similar, but transplacental transmission does not occur. Human infections are sporadic and occur worldwide.

TRANSMISSION:

Infection is generally in dirt-eating young children who ingest T. canis or T. cati eggs from soil or sand contaminated with animal feces, most often from puppies. Direct contact with infected animals does not produce infection, as the eggs require a 3 to 4 week extrinsic incubation period to become infective; thereafter, eggs in soil remain infective for months to years. In humans, hatched larvae are unable to mature and continue to migrate through the tissues for up to 6 months. Eventually they lodge in various organs, particularly the lungs and liver and less often the brain, eyes, and other tissues, where they produce eosinophilic granulomas up to 1 cm in diameter.

DISEASE IN ANIMALS:

The first indication of infection in young animals is lack of growth and loss of condition. Infected animals have a dull coat and often are "potbellied". Worms may be vomited and are often voided in the feces. In the early stages, pulmonary damage due to migrating larvae may occur; this may be complicated by bacterial pneumonitis, so that respiratory distress of variable severity may supervene. Diarrhea with mucus may be evident. In severe infections of puppies, verminous pneumonia, ascites, fatty degeneration of the liver, and mucoid enteritis are common. Cortical kidney granulomas containing larvae are frequent in young dogs.

DISEASE IN MAN:

Migrating larvae induce fever, cough, wheezing; hepatomegaly, and sometimes splenomegaly and lymphadenopathy are present. The acute phase may last 2-3 weeks, but resolution of all physical and laboratory findings may take up to 18 months. Leukocytosis is marked due to eosinophils. Hyperglobulinemia occurs when the liver is extensively invaded. Ocular toxocariasis results in a eosinophilic granuloma of the retina that may be mistaken for retinoblastoma.

DIAGNOSIS:

ELISA, no parasitic forms can be found by fecal exam.

TREATMENT:

Thiabendazole, Mebendazole, or Ivermectin. Corticosteroids, antibiotics, antihistamines, and analgesics are given for symptomatic relief. Treatment for Ocular Toxocariasis includes the above plus vitrectomy and laser photocoagulation.

PREVENTION/CONTROL:

Disease in humans is best prevented by periodic treatment of puppies, kittens, and nursing dogs and cats. Children should be supervised to prevent pica; their hands should be washed after playing in soil and sand; and play areas should be protected from animal feces.