摘要：Baylisascaris procyonis , a common ascarid of the raccoon ( Procyon lotor ), is known as the causative agent of a clinical central nervous system (CNS) disease, visceral and ocular larva migrans are found in humans as well as a variety of wild and domestic mammals and birds in North America. Although raccoons are indigenous animals in North and Central America, over 20, 000 raccoons have been imported to Japan as pets at home since 1977. Many of the raccoons, having escaped from the houses, are reported to inhabit the wildlife areas of the central part of Honshu and Hokkaido. The present study was carried out to elucidate the following: the prevalence of B. procyonis in raccoons in Japan; the occurrence of experimental larva migrans in mice; the distribution of larvae among the tissue of mice and pathological changes of the tissue; the effect of anthelmintics against the manifestation caused by the worms; and whether or not the larvae develop into adults in dogs and cats. The results are summarized as follows. 1) Of the 291 raccoons examined, eggs of B. procyonis were found in 39.9% of zoo-kept animals, 8.1% of animals stocked by traders and 7.7% of pets kept at home. No eggs was found in the 37 wild raccoons examined. 2) All mice that were inoculated with 100 embryonated eggs sickened 10 to 14 days post inoculation (PI) and died 14 to 19 days PI with CNS symptoms such as circling, torticollis and rolling. It seems that the severity of the CNS symptoms in mice depends on the dose of the inoculation of the embryonated eggs. 3) The larvae invaded the small intestine wall of mice during 6 to 12 hours after hatching in the stomach and migrated to somatic tissue in 4 days through liver and lungs, where they migrated in 3 days. The larvae were already found in the brain at 3 days PI in a few mice. An average of 3-5% of embryonated eggs inoculated per os via stomach tubes was found as larvae in the brain. 4) The larvae grew considerably in the tissue of the mice during migration, reaching twice their initial body length at 4 days PI and five times the initial length, 1400-1600μm, at 15 days PI in the brain. 5) Some anthelmintics, albendazole, thiabendazole and mebendazole, appear to be effective against the visceral larva migrans of mice when the drugs were given daily for 10 consecutive days, the first dose 24 hours after inoculation of the embryonated eggs to mice, but ineffective when they were given for 3 consecutive days after commencing at 7th day of the inoculation of the embryonated eggs. 6) Four of the 7 young dogs which were inoculated with either the embryonated eggs or the larvae of the parasite showed the adult worms in the small intestine in 42-48 days. This finding suggests that dogs may play the role of preservative host for B. procyonis instead of raccoons as the natural final host. The manifestation of the diseases caused by the raccoon ascarid appears to be more severe and fatal in comparison with that of the larva migrans of dog ascarid, Toxocara canis , in the present study. Thus, the prevalence of B. procyonis parasitizing the raccoons, which are kept as pets or inhabit the wildlife areas in Japan, deserves greater attention in considering the transmission of the parasite to humans.
