Epidemiology

Toxocara canis has a cosmopolitan distribution. Although it seems more common in wet tropical areas, the parasite is found both in countries with severe winters and those with dry summers. In Sweden, the first serologically confirmed case of toxocarosis was published in 1979 (Carlson et al. 1979) and in 1996 the first report of VLM in an adult Norwegian was published (Lund-Tonnesen 1996). A seroepidemiological survey of young healthy Swedish adults (n = 323) gave the prevalence of 7% indicating that subclinical toxocarosis occurs in healthy Swedes. In the sera of patients (n = 175), suspected of having contracted toxocarosis, 25% were seropositive suggesting that clinically covert toxocarosis exists in Sweden (Ljungstrom and van Knapen 1989). In Lithuania, a seropositive reaction was observed in 11.5% of sera (n = 739) from patients with clinical symtoms suggesting VLM (Bajoriniene and Balkjawiczius 1988). At Toronto's Hopital for Sick Children a retrospective search for cases during the period 1952 through 1978 was performed. Only 18 VLM and three possible OLM cases were identified, indicating that VLM poses little risk to the health of children in the Toronto area (Fanning et al. 1981).

Toxocara canis infection has also been reported in 28% of wild red foxes (n = 192) collected all over Sweden, with 14% of foxes above latitude 67°N infected (Christensson 1983, 1988).

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However, no Toxocara infection was observed in Arctic foxes taken on Banks Island, The Northwest Territories (Eaton and Secord 1979). In the metropolitan area of Copenhagen 68 red foxes were collected and Toxocara eggs could be detected in 23.5% and T. canis worms were recovered from 17/21 (81%) of these foxes (Willingham et al. 1996).

During the years 1971-1981 the National Veterinary Institute, Sweden, analysed the occurrence of T. canis in Swedish dogs by autopsy (n = 90) and routine stool examination (n = 19044). The prevalence was found to be 5 and 6.5%, respectively (Christensson 1983). In routine stool samples (n = 426) from dogs sent to the laboratory of The Norwegian College of Veterinary Medicine, Norway, during 19811982, Toxocara was diagnosed in 4%. In hospitalized dogs (n = 2290), during the 5-year period, 19781982, only 0.7% had Toxocara eggs in their stool (Tharaldsen 1983). In Halifax, Nova Scotia, the prevalence of T. canis eggs in stray dogs (n = 474), was found to be 26.6% and the prevalence was noticably greater in pupies, 56.1%, than in mature dogs, 11.9% (Malloy and Embil 1978). 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. Of 13 sandpits, 38.5% were found infected with Toxocara spp.

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