THE POTENTIAL FOR DENGUE IN SOUTH-AFRICA - VECTOR COMPETENCE TESTS WITH DENGUE 1 AND 2 VIRUSES AND 6 MOSQUITO SPECIES

Six mosquito species, selected because their prevalence, distribution and ecology favoured them as potential vectors of dengue (DEN) in Sout h Africa, were tested for vector competence with DEN 1 and 2 viruses. After intrathoracic inoculation with DEN 1, head squash infection rate s (HSIRs) by the indirect fluorescent antibody test were 92-100% in al l species except Aedes demeilloni, for which rates were <40%. After an infective blood meal containing DEN 1 and DEN 2 virus respectively, A e. demeilloni, Ae. simpsoni and Eretmapodites quinquevittatus were ref ractory to infection, while the 3 other species became infected. Five populations of Ae. aegypti each 'transmitted' both serotypes into capi llary tubes. With DEN 1, HSIRs and transmission rates (TRs) varied fro m 11% to 54% and 67% to 100%, while with DEN 2 they ranged from 19% to 46% and 71% to 86%. The mean vector competence index (VCI) was highes t for Durban (0.47 for DEN 1 and 0.34 for DEN 2), while VCIs for the r emaining populations varied from 0.13 to 0.28 (DEN 1) and 0.18 to 0.23 (DEN 2). With DEN 1, HSIRs for Ae. strelitziae and Ae. furcifer were 33% and 3% respectively, but no transmission occurred. With DEN 2, res ults for Ae. strelitziae were HSIR=56%, TR=29% and VCI=0.16, while val ues for Ae. furcifer were HSIR=12%, TR=50% and VCI=0.06. It is conclud ed that populations of Ae. aegypti are potentially the best vectors fo r both serotypes of the virus and that the Durban population could act as the most efficient vector in an urban or peri-urban epidemic. Ae. strelitziae could act as a secondary vector of at least DEN 2 on the N atal coast. Ae. furcifer must be regarded as a potential, though poor, vector of DEN 2 virus in rural areas of the tropical region of South Africa.