The prevalence of Stephanofilaria sp in buffalo fly, Haematobia irritans exigua, in Central Queensland

Buffalo fly (Haematobia irritans exigua) infestations of cattle are associated with characteristic lesions, the initial cause of which has been attributed to a filarial nematode of the genus Stephanofilaria, for which the fly acts as a vector. Survey work in the 1980s estimated the prevalence of microfilaria in female buffalo fly in Queensland at 2.91%. Since then no information has been published and the current prevalence of microfilarial infection in buffalo fly is not known. Buffalo fly were collected from four geographically distinct sites in Central Queensland in mid-summer 2004 and were dissected to estimate Stephanofilaria sp. infection rates. Larval stages of the nematodes were recovered from female flies from all four sites and the percentage of female flies from which nematodes were recovered ranged from 29% to 57%. The average number of larvae recovered from infected female flies ranged from 1.25 to 1.75. Whereas no infected male flies were found from Sites 2-4, larvae were recovered from 43% of male flies collected at Site 1. This high prevalence of filarial infection in buffalo flies implies a correspondingly high level of transmission to cattle in Central Queensland.