Toxocariasis--an unlikely cause of Palm Island mystery disease.

After the suggestion was made that the "Palm Island mystery disease" might have been an epidemic of visceral larva migrans that was caused by the flying fox parasite, Toxocara pteropodis, work was undertaken to elucidate this nematode's life-cycle and pathogenicity. Studies of infections in various laboratory animals have shown unexpectedly variable susceptibility patterns, with mice harbouring most larvae for the longest time period. However, in all susceptible animals (which include mice, guinea-pigs and suckling rats), the larvae demonstrated marked hepatotropism. Experimental infections in monkeys demonstrated that primates are susceptible to this infection, but large doses of 20,000 infective eggs produced blood eosinophilia and focal granulomatous hepatitis without clinical disease or biochemical abnormalities in the blood. It is concluded that humans are susceptible to larval infections with this nematode, but that clinical manifestations would be unlikely to develop.