Natural infections of blackflies with larvae of zoonotic Onchocerca spp. in northeast Japan.

Abstract

Dissections of female blackflies collected while attacking a cow at the Omyojin Farm, Iwate, northern Japan showed that 4.4% of 1, 104 Simulium daisense, 0.8% of 913 S. aokii, 0.5% of 741 S. iwatense and 0.9% of 340 S. nikkoense examined were naturally infected with filarial larvae. There were at least two types of third-stage larvae assignable to Onchocerca, of which type A found in S. daisense and S. aokii measured 914-1, 212 μm long by 26-29 μm wide while type B found in S. daisense had its body size of 369-477 μm long by 14.9-17.9 μm wide. Morphometric observations suggest that types A and B each correspond to types I and III previously recorded in Kyushu, southwest Japan as the third-stage larvae of bovine Onchocerca (i.e., O. sp. and O. lienalis). This is the first record for natural infection of blackflies in Honshu (main island of Japan) with zoonotic Onchocerca larvae.