| Summary: | Hard ticks taken from the Japanese serow, Capricornis crispus, in Yamagata Prefecture, Honshu, harboured infective larvae of onchocercid filariae after incubation from the 22nd to the 158th day. Haemaphysalis flava and H. japonica contained one to eight filarial larvae; females, males and a nymph of the ticks were infected. The 44 infective larvae recovered were 612–1,370 μm long, and 11 of them, 930–1,340 μm long, were studied in detail. The larvae possessed the morphologic characteristics of the larvae of the genus Cercopithifilaria, namely an oesophagus with a posterior glandular part, no buccal capsule and a long tail with three terminal lappets. Five types (A to E) of infective larvae were identified based on the morphologic characteristics. While to date five species of Cercopithifilaria have been described from the Japanese serow, a specific identification of the larvae found in this study was generally not possible. Only type E larvae could be tentatively assigned to Cercopithifilaria tumidicervicata, as they had a cervical swelling similar to that of the adults of this species. A key for the identification of the five larval types is presented. The study presents circumstantial evidences indicating that H. flava and H. japonica may transmit Cercopithifilaria spp. to Japanese serows. It also suggests the possibility that such filarial larvae will be found in hard ticks anywhere, because Cercopithifilaria is distributed worldwide, though this genus generally goes unnoticed, as its microfilariae occur in the skin, not in the blood, of host animals.
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