Conference in 6th EPIZONE Annual Meeting "Viruses on the move" 

June 12^nd, 2012

Gallardo C., Nieto R., Mur L., Soler A., Pelayo V., Bishop R., Sanchez-Cordon PJ., Martins C., Sanchez-Vizcaino JM. and Arias M.

African swine fever (ASF) is a complex and lethal viral disease of swine with significant socio-economic impact in the developed and developing world. The disease has a major negative effect on national, regional and international trade and constrains pig production by livestock farmers in affected areas in Sub-Saharan Africa and in the Caucasus region, where the disease was first identified in 2007.
Transmission of African swine fever virus (ASFV) can occur in a sylvatic or in a domestic pig cycle, with or without tick involvement. Depending on the presence or absence of wild suids and arthropod vectors and the type of pig production system, the epidemiology varies substantially between countries, regions and continents. In East Africa the disease is maintained by the concurrent existence of different transmission cycles involving asymptomatic wild African pigs (Phacochoerus and Potamochoerus spp.), soft ticks of the genus Ornithodorus, mainly O. porcinus and domestic pigs with all the 22 known ASFV genotypes circulating. Moreover, recent investigations in eastern Africa have demonstrated a complex epidemiological situation in porcine local breeds faced to tolerant against ASF combined with a lack of
humoral response co-existing with a high viral load. The capacity of the available diagnostic assays to detect ASF specific antibodies with high specificity and sensitivity independent of the viral genotypes circulating in a particular region has been recently demonstrated. So, the complex epidemiology described in East African regions might be related to “tolerant” indigenous pigs and it might reside in the immunogenetics and genetic characteristics of the indigenous pig populations, rather than being due to owner properties of the ASFV strains. This hypothesis was supported by the results obtained in a comparative experimental infection by the inoculation of Kenyan “indigenous pigs” and European domestic pigs using selected ASFV Kenya ASFV isolate belonging to genotype X. A significant delay of onset of ASF in “indigenous pigs” was observed with an unclear, unspecific and non-patognomonic picture of the disease together with a delay in the detectable antibody response. There is evidence that domestic pigs from East African countries such as Kenya exhibit some introgression of genetic material from the Asian centres of wild boar domestication and are therefore not identical to European and West African pig breeds. Consistent with the hypothesis of differences in serological responses between domestic pig breeds, previous findings indicate that the viraemia in bush pigs generally lasted longer than in warthogs in absence of seroconversion. These facts attributable to the phenotype of ‘indigenous’ African pigs might increase the risk of the endemicity of ASF and virus spreading and thus, difficult the control and success of ASF eradication

	Centro de Investigación en Sanidad Animal (CISA). Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA).
	Departamento de Sanidad Animal. Facultad de Veterinaria. Universidad Complutense (UCM).
	International Livestock Research Institute (ILRI).
	Facultad de Veterinaria. Universidad de Córdoba (UCO).
	Servicio de Inmunología Viral y Medicina Preventiva (SUAT). Centro de Vigilancia Sanitaria Veterinaria (VISAVET). Universidad Complutense (UCM).