Setaria digitata infections in cattle: parasite load, microfilaraemia status and relationship to immune response

A total of 110 cattle were examined in an area endemic for Bancroftian fila riasis for the prevalence of infection of the bovine filarial parasite Seta ria digitata. About 12.5% of cattle were found to harbour both adult worms in the peritoneum and microfilariae (mf) in circulation; 70% of the cattle were amicrofilaraemic but with an adult worm infection. A third group of ca ttle (16.5%) was free of detectable mf and adult worms. The presence of adu lt worms and/or mf did not influence the antibody levels to any of the four antigen preparations of S. digitata. However, there was a significant inve rse relationship between the presence of antibodies to microfilarial sheath s and the absence of circulating mf as shown by the immunoperoxidase assay. Cattle immunoglobulin containing high titres of anti-sheath antibodies cle ared circulating microfilariae very effectively in Mastomys coucha thus dem onstrating the protective nature of anti-sheath antibodies in eliminating c irculating microfilariae in vivo.