Transmission of the human filarial parasite Mansonella Ozzardi by Culicoides phlebotomus (Williston) (Diptera: Ceratopogonidae) in coastal north Trinidad

Between June 1976 and November 1977, man-baited and truck-trap collections of haematophagous Diptera were made on the foreshore of Las Cuevas Bay, north Trinidad, close to a fishing village where Mansonella ozzardi infections are prevalent in man. Culicoides phlebotomus (Will.) predominated in all collections, forming 96·1% of the total catch. Analysis of blood-meals from engorged C. phlebotomus collected by truck trapping at sunset indicated frequent feeding on mammals, with feeds on man comprising 47% of those identified. Filarial larvae were found in 0·8% of 6767 females of C. phlebotomus captured on man, and five (0·08%) had infective larvae of M. ozzardi. Similarly, 1·3% of 7028 females obtained by truck trapping were infected, including nine (0·13%) with infective larvae. Growth rates of M. ozzardi in C. phlebotomus were determined by experimental infection and were used to estimate daily survival rates of wild-caught females of C. phlebotomus based on filarial growth stages found in them. The daily survival rate varied from 85 to 95% in flies 1–3 days after infection to 69% in flies six days after infection. It was estimated that a person spending one hour on the beach every morning would receive 38 infective bites from C. phlebotomus per annum.