DONKEYS AS RESERVOIRS OF AFRICAN HORSE SICKNESS VIRUS

Investigations have been carried out to elucidate the possible role of the donkey in the epidemiology of African horse sickness (AHS). These studies have shown that despite the absence of pyrexia or other obser vable clinical signs, donkeys become infected with virulent AHS virus serotype 4 (AHSV 4) and that they develop a viraemia which can persist for at least 12 days, albeit at a comparatively lower titre than that recorded for similarly infected ponies. AHSV fl, showed a similar tis sue tropism in the pony and donkey but the virus appeared to replicate less efficiently in donkey tissues. The only gross pathological chang es observed in the donkeys post mortem were increased fluid accumulati on in the serosal lined compartments, particularly the peritoneal cavi ty, and petechial and ecchymotic haemorrhages on the left hepatic liga ment. The absence of infectious virus or viral antigens in any of the tissues collected at 14 and 19 days post inoculation (dpi) from 6 expe rimental donkeys suggest that, though susceptible to infection, the do nkey is unlikely to be a long term reservoir for AHSV. Although AHSV 4 was detected in all 6 donkeys following the primary inoculation, no v irus could be isolated from blood collected from two donkeys subsequen tly challenged with a second virulent virus, AHSV 5. Data generated fr om virus neutralisation tests showed a second primary antibody respons e, against AHSV 5, in these donkeys at 12 dpi. In contrast, the boost in antibody levels detected from 5 dpi, as measured by ELISA, was prob ably due to an anamnestic response against the AHSV group-specific vir al proteins. Homogenised spleen tissue, collected post mortem from a d onkey 7 dpi with AHSV 4, caused a lethal, cardiac form of AHS when ino culated into a susceptible pony.