PROTEOLYTIC CLEAVAGE OF VP2, AN OUTER CAPSID PROTEIN OF AFRICAN HORSESICKNESS VIRUS, BY SPECIES-SPECIFIC SERUM PROTEASES ENHANCES INFECTIVITY IN CULICOIDES

Purified African horse sickness virus (AHSV) was fed, as part of a blo od meal, to adult females from a susceptible colony of Culicoides vari ipennis, established in the insectories at the Institute for Animal He alth, Pirbright Laboratory, UK. The meal consisted of heparinized bloo d obtained from ovine, bovine, equine (horse and donkey) or canine sou rces spiked with AHSV serotype 9 (AHSV9). The infectivity levels obser ved for C. variipennis varied significantly, according to the source o f the blood sample. Comparison of the protein profiles obtained from A HSV9 incubated with the individual serum of plasma samples indicated t hat some species-specific serum proteases were able to cleave the oute r capsid protein, VP2. The blood samples containing serum proteases th at were able to cleave VP2 also showed an increase in infectivity for the insect vector when spiked with purified AHSV.