On the Transition of Canine Heartworm Prevalence among Dogs in Nagasaki City, Western Japan. : 1. The filarial prevalence among dogs in the city

A field survey on the microfilarial prevalence of Dirofilaria immitis among house dogs and stray dogs was carried out in Nagasaki City, Western Japan, in 1977. In addition, all of the stray dogs examined for microfilariae were dissected to recover the adult worms of D. immitis. Out of 1,721 house dogs examined 563 or 32.7% were found to have microfilariae of D. immitis in their peripheral blood. In the one-year-old dogs, the microfilarial prevalence was already 8.8%. The prevalence reached 29.5% in the two-year-old and ranged from 38.1% to 51.9% in the older ones. The spatial distribution of the positive dogs in Nagasaki City suggests that the canine heartworm was transmitted more intensively in the suburban areas than in the urban or rural areas in the city. Out of 167 stray dogs, which were caught in the city and kept at the City Dog Pound, 74 or 44.3% were found to have microfilariae and/or adults of D. immitis. No dogs having Dipetalonema reconditum microfilariae were found in the city. The results of the present survey were compared with those of the former similar surveys in the city. The higher microfilarial prevalence of D. immitis in the present survey suggests that the canine heartworm is being transmitted more intensively than before and this may indicate the increasing possibility of the transmission to man