A. I. Khalafalla and G. A. El-Dirdiri
Department of Microbiology, Faculty of Veterinary Science,
University of Khartoum, Shambat, 13314 Khartoum North
The aim of this work was to determine the efficacy of two commercially available camelpox (CP) vaccines, namely Ducapox live attenuated (LA) vaccine produced in South Africa and an inactivated adjuvant (IA) vaccine produced in Morocco. Inoculation of the LA vaccine virus into cell culture produced typical growth characteristics of a CP virus (CPV) with high virus titre. Sterility tests proved the safety of the vaccine. Young camels 12 to 18 months of age were divided into groups and vaccinated with both vaccines with single and two doses regimes. Humoral immune response was measured by serum neutralisation test (SNT) and passive haemagglutination test (PHT). Cellular immune response was measured by the delayed type-hypersensitivity (DTH) reaction.
Camels vaccinated with both vaccines and later challenged with a virulent CPV, showed no clinical signs of disease or pox lesions. Development of the humoral antibody response started on the 2nd week post vaccination (PV) for both vaccines and a booster dose increased the antibody titre significantly. The IA vaccine, however, induced a low level of antibodies. In the DTH experiment, all camels vaccinated with both vaccines reacted positively with a remarkable increase in skin thickness as compared to controls indicating a sound cell-mediated immune (CMI) response. The increase in thickness was relatively greater in dromedaries vaccinated with the LA than with the IA vaccine. Field vaccination trials revealed that both vaccines induced a weak immune response in camels less than 6 months of age and also older than 4 years of age. This can be explained by possible existence of maternal antibodies or the immaturity of the immune system in camel calves, and the occurrence of pre-vaccination antibodies in adult camels. Good immune response as measured by serological tests, developed in the age group of 1 to 4 year-old camels.
Both vaccines used in this study were safe, potent and immunogenic since they induced humoral and cellular immune response and protected vaccinated dromedaries against challenge. Camels vaccinated with the IA should be revaccinated 8 weeks post-primary vaccination, while one dose of the LA vaccine is enough to sustain protection for at least one year. The appropriate age for vaccination for both vaccines is 6 months. The Passive Haemagglutination Test was found useful for serology of CP; it is easy to perform, less expensive and also sensitive when compared with the serum neutralisation test.
Keywords : Camelpox vaccines, DTH, field trials, SNT