A comparison of the susceptibility of the biting midge Culicoides imicola to infection with recent and historical isolates of African horse sickness virus

The susceptibility of Culicoides (Avaritia) imicola Kiefer (Diptera: Ceratopogonidae) to 21 isolates representing all nine known serotypes of African horse sickness virus (AHSV), recovered from clinical cases of the disease in South Africa during 1998-2004, was compared with its susceptibility to approximately 40-year-old isolates stored at the Agricultural Research Council-Onderstepoort Veterinary Institute. Field-collected C. imicola were fed through a chicken skin membrane on sheep blood spiked with one of the virus isolates to a concentration in the range of 5.6-7.5log 10TCID50/mL. After 10 days incubation at 23.5 degrees C, five of the nine historical serotypes (AHSV-1, -2, -3, -7 and -9) could not be isolated from C. imicola. All nine serotypes were recovered for the 21 recent isolates, for 16 of which the virus recovery rates were higher than for the corresponding historical isolates. These results emphasize the need to assess the oral susceptibility of local Culicoides populations to viruses in circulation during outbreaks in order to estimate their vector potential.