Biological and clinical responses of West African sheep to Crimean-Congo haemorrhagic fever virus experimental infection

West African sheep appear to play a central role as virus hosts in the main tenance cycle of Crimean-Congo haemorrhagic fever (CCHF) virus in endemic a reas and also because of their role as a principal host of the CCHF virus t ick vector. In an effort to clarify CCHF epidemiological significance in sh eep, we studied the biological and clinical aspects of sheep experimentally infected with CCHF virus. West African sheep breeds were infected either b y intraperitoneal inoculation or by infestation with experimentally CCHF-vi rus-infected ticks (Hyalomma truncatum). A total of 17 sheep including cont rols as well as 5 lambs from their progeny were monitored. A moderate but c onstant fever was observed (39.7 degrees C +/- 0.3) which correlates with t he viraemia. Virus was reisolated from blood samples taken from day 3 to da y 9 postinfection (p.i.) at a mean titre of 3.3 log LD50/ml. The virus was detected for a period of time of 7 days in non-immune sheep and for less th an 4 days in previously immunized sheep. In non-immune sheep, antibody dete cted by ELISA showed an IgM response on day 7 p.i., followed by an IgG resp onse one day later. Five infected sheep, surveyed for liver and kidney biol ogical markers, showed hepatic dysfunction with a moderate serum aspartate transferase rise to 210 U/l. Out of four sheep tested for blood markers, tw o showed an abnormal blood cell count, with marked neutrophilia of up to 63 % lasting for two weeks. Infected pregnant ewes produced antibodies in thei r milk at a significant titre (1:1,000), and antibodies were recovered in t he sera of nursing lambs from their first meal to 50 days after birth. Thes e findings are discussed; they demonstrate that, in spite of a high turnove r of local sheep herds (median age of 3 years) and long-term CCHF antibody persistence (> 3 years), sheep can be infected and efficiently transmit the virus at least once in a lifetime.