Toxocara canis has a cosmopolitan distribution. The parasite is found both in countries with severe winters and in those with dry summers, although it seems more common in wet tropical areas. In Sweden the first serologically confirmed case of toxocarosis was published in 1979 (Carlson et al. 1979), and in 1996 the first report of visceral larval migrans (VLM) in an adult Norwegian was published (Lund-Tonnesen 1996). A seroepidemiological survey of young healthy Swedish adults showed 7% prevalence, indicating that subclinical toxocarosis occurs in healthy Swedes. In the sera of patients suspected of having contracted toxocarosis, 25% were seropositive suggesting that clinically covert toxocarosis also exists in Sweden (Ljungstrom and van Knapen 1989). In Stockholm, 86 sandboxes were investigated for Toxocara eggs and 32% were found to be infected (Christensson 1983, 1988). A similar figure was also observed in Oslo, where of 13 sandpits sampled, 38.5% were found infected with Toxocara spp. Toxocara canis infection has also been reported in animals, and 28% of wild red foxes collected from all over Sweden were found to be positive. Fourteen per cent of foxes above latitude 67°N were infected (Christensson 1983, 1988). In the metropolitan area of Copenhagen, stools from red foxes were collected and Toxocara eggs could be detected in 23.5% and T. canis worms were recovered from 81% of these foxes (Willingham et al. 1996). An autopsy of 230 stray cats gave further evidence of the high endemicity of these worms in the north as 79% of them were infected with Toxocara cati (Engbaek et al. 1984).

During the years 1971-1981 the National Veterinary Institute of Sweden analyzed the occurrence of T. canis in Swedish dogs by autopsy and routine stool examination (n = 19044). The prevalence was found to be 5 and 6.5%, respectively (Christensson 1983). In routine stool samples from dogs sent to the laboratory of The Norwegian College of Veterinary Medicine during 1981-1982, Toxocara was diagnosed in 4% of the samples. In hospitalized dogs, during the five-year period of 1978-1982, only 0.7% had Toxocara eggs based on stool sample examination (Tharaldsen 1983).

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