DEVELOPMENT OF ONCHOCERCA-CERVICALIS TO THE 3RD LARVAL STAGE IN SIMULIUM-PICTIPES

The objective of this study was to assess the ability of a temperate b lack fly, Simulium pictipes, to support larval development by Onchocer ca cervicalis, a filarial parasite of horses normally associated with ceratopogonid vectors. A proportion of both freshly isolated and cryop reserved microfilariae (MF) inoculated intrathoracically into S. picti pes completed development to the third larval stage (L3) in the thorac ic and cephalic musculature. The first and second molts occurred as ea rly as days 6 and 7 of infection, respectively. Relative to the course of O. cervicalis infection in a natural vector, Culicoides nubeculosu s, the frequency of development in S. pictipes was low. Black flies in oculated with 50 freshly isolated MF ultimately yielded a mean of 3.3 L3 per fly, representing 6.5% of the original inoculum. In contrast, 2 .1% of the cryopreserved MF were recovered as L3. Migration of L3 from the thoracic musculature to the heads and mouthparts of infected flie s could not be ascertained. The mean length of L3 recovered from S. pi ctipes was 579 mu m, approximately 35% shorter than L3 derived from th e natural vector. These results demonstrate that S. pictipes will supp ort development of a proportion of inoculated O. cervicalis MF, making it a potential source of these parasite stages albeit an inefficient one. The relevance of this finding to the development of laboratory mo dels for the study of onchocerciasis is discussed.