Determination Of Optimal Viral Dos Immunological Response And Survival Rate In Local And Exotic Pigs Experimentally Infected With Africans Swine Fever Virus

Abstract

Two genotypes of African swine fever virus were identified around East Africa based on molecular characterization of P72 and P54 genes. These are designated genotypes IX and X. whereas genotype IX has been associated with recent lethal ASF outbreaks in East Africa; genotype X has been associated with infections that apparently did not produce clinical responses, in south west Kenya. Biological and clinical characteristics of these viruses have not been studied in experimental infections. This study aimed to conduct an in vivo biological characterization of ASFV genotype IX isolate 1033 originating from an ASF outbreak in Western Kenya, that has been shown to be genetically closely related to many outbreak associated viruses in Kenya and Uganda isolated from both local and exotic breed pigs. The specific aim of the experiment was to find out the titration of the virus that was able to cause clinical disease following experimental infection as well as to study the clinical symptoms induced by the different dilutions in order to determine a useful challenge dose for vaccination research. Housed European breed and local free range domestic pigs were challenged with doses containing between 10-4and 10-5 HAD50 (Haemadsorbing units), of the highly virulent ASFV isolate 1033 by inoculation using the intramuscular route. Pigs were monitored for clinical progression and post mortem lesions and these were compared to previously describe experimental and natural infections. Samples were analyzed for virus titres, antibody and cellular responses in vitro. The statistical analyses were carried out using GraphPad Prism and Microsoft Excel. The data obtained from the experiment gave the most effective dose for virus infection hence provided insight into the host response to infection by this particular isolate. For both exotic and local pigs, the clinical signs were characterized by loss of appetite, fever of between 39.6 and 41.4oC, foul smelling diarrhoea, lateral recumbence and death. For the exotic, there were skin lesions characterized by cyanosis and haemorrhages. The main pathological lesions were characterized by generalized haemorrhages, coagulation disorders, oedema of the lungs and lymph nodes and gastroenteritis. The estimated optimal viral dose for the exotic pigs ranged between 10-6 to 10-7HAD50/ml (titres) and 10-5.4HAD50/ml for the local pigs. The mean optical density values for the immune response of exotic pig were 0.17 and 0.18 for the local pigs. Average survival time for the exotic pigs was 10 days post infection and 12 days post infection for the local pigs. The results achieved were aimed at providing basic information which will in future assist in vaccine search for ASF control and assist in developing guidelines for veterinarians regarding quarantine and control measures in naive pigs brought in and for outbreak control. Further research should be directed towards identifying the epitopes responsible for the increased survival of local pigs which can be used for vaccine development. A lot needs to be done on the African swine fever genome and the genetic material in the local pigs that enables partial survival to ASF infection should be identified and modified to see if the virulence of ASF will reduce or enable the exotic pigs survive ASF infection without clinical disease.