The epidemiology of Parafilaria bovicola in the Transvaal Bushveld of South Africa.

A total of 20 375 flies collected off cattle on 12 farms over 36 months were identified and examined for 3rd stage P. bovicola. The 3 vector species accounted for 64.1% of the flies collected and were the only fly species found to be infected. Musca lusoria was clearly the dominant vector fly, although large numbers of Musca sp. A appeared regularly between February and April each year. This phenomenon, coupled with high numbers of M. lusoria throughout most of the year, led to an increase in the numbers of vector flies from their lowest level in June to a peak in February-April. Of the 13 070 vector flies examined for 3rd stage larvae only 64 (0.52%) were positive; of these 41 were M. lusoria and 17 Musca sp. A. No positive male flies were found. Incubation of wild-caught flies for up to 13 days at 27 degrees C noticeably increased the larval recovery rate. Flies were found to be infected mainly from August-March. Infected M. lusoria were recorded from July-March and infected Musca sp. A from January-May. Only 6 infected M. xanthomelas were collected and this was during the period August-December, when most ovipositional blood spots occur on cattle. It is concluded that P. bovicola transmission in the Bushveld is not correlated with peak periods of bleeding but rather with high numbers of vector flies, the various species augmenting each other so that transmission may take place almost throughout the year.