Current epidemiologic and therapeutic aspects of imported malaria in Japan were examined from 1980 to 1995 by sending questionnaires every year to more than 1, 500 major hospitals. Imported malaria gradually increased in number from 1980 and became more than 100 from 1990. The number of cases with falciparum malaria increased in number from around 1993 and became comparable to the number of vivax malaria. As the presumptive place of contraction, Africa has been increasingly important, especially for falciparum malaria. Recently the number of foreign cases, most often from India, has been becoming rather high, ranging 24 to 36% of the total cases. We found 7 fatal cases with falciparum malaria, all of whom seemed to be infected in Africa except for a Japanese female due to domestic transfusion malaria. Recrudescence and relapse were detected at significant rates, i.e., 2.2 to 9.5% and 5.4 to 17.2% of the cases with falciparum and vivax malaria analyzed, respectively. Concerning the antimalarial drugs available in Japan, mefloquine has been the drug of choice after the Research Group for Development of Chemotherapeutic Agents against Tropical Parasitic Diseases supported by the Japanese Ministry of Health and Welfare started its import for clinical trial. Further efforts are still needed to improve the diagnostic and therapeutic capacity against imported malaria in Japan.

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In 1988-1989, microfilariae of an unidentified Onchocerca species were found in the skin of eight of the 16 cattle aged at least 5 years that were examined in Oita, Kyushu, Japan. Adult worms were not found in cattle, but the microfilariae taken from skin snips, which have coiled posterior parts, were grown to the infective stage in simuliid. In 1997, both adults and microfilariae of 0. suzukii were recovered from Japanese serows (Capricornis crispus) in Yamagata, Honshu. Such microfilariae from serows, reported here for the first time, had coiled posterior parts and measurements {130-160 (mean, 140) pm long and 4-6 (5) μm wide} close to those from cattle. The findings showed that the Onchocerca sp. in cattle in Kyushu is O. suzukii, a transfuge parasite from the Japanese endemic bovid, C. crispus.

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From 1991 to 1992, the prevalence of Dirofilaria immitis was clarified in stray dogs from Okinawa, Kume where the first survey was carried out, Miyako, and Ishigaki Isls. of Okinawa Prefecture, Japan. The number of dogs examined was 504 in Okinawa, 13 in Kume, 139 in Miyako and 184 in Ishigaki Isls. In the islands except Miyako Is., about 40% of adult dogs (one year or older) were determined to be infected with D. immitis; but in Miyako Is., 8.3% of adult dogs were positive. All the worms recovered were D. immitis. In Ishigaki Is., the incidence was higher than that reported by Asato et al. (1985). However, in Miyako Is. where young dogs were examined, the incidence was similar to that reported by Asato et al. (1985). In Kume Is., the incidence of D. immitis in house dogs was also examined by the presence of the microfilariae, being 25.5% in outdoor dogs reared outside and none in dogs retained indoor.

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Cercarial maturation time, duration of cercarial emergence and number of cercariae released were studied in five subspecies of laboratory-reared Oncomelania hupensis (Oncomelania hupensis nosophora, O. h. hupensis, O. h. formosana, O. h. chiui and O. h. quadrasi) infected with three different geographic strains of Schistosoma japonicum. O. h. nosophora, O. h. hupensis and O. h. formosana were the most suitable host snails for the Japanese, Chinese and Taiwanese strains of S. japonicum, respectively. The cercarial maturation time in the most suitable host snails were 8 weeks for the Taiwanese strain of S. japonicum and 10 weeks for the Japanese and Chinese strains after exposure to 5 miracidia. The duration of cercarial emergence were 9 weeks for the Taiwanese strain, 17 weeks for the Chinese strain and 16 weeks for the Japanese strain. The duration of cercarial emergence was similar in the remaining subspecies, but the maturation time of cercariae was longer. For numbers of cercariae emergenced from snails, the most suitable host snails had a tendency to released more cercariae than the remaining snails.

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