Evidence for the presence of African swine fever virus in an endemic region of Western Kenya in the absence of any reported outbreak.
BACKGROUND
African swine fever (ASF), caused by African swine fever virus (ASFV), is a severe haemorrhagic disease of pigs, outbreaks of which can have a devastating impact upon commercial and small-holder pig production. Pig production in western Kenya is characterised by low-input, free-range systems practised by poor farmers keeping between two and ten pigs. These farmers are particularly vulnerable to the catastrophic loss of livestock assets experienced in an ASF outbreak. This study wished to expand our understanding of ASFV epidemiology during a period when no outbreaks were reported.


RESULTS
Two hundred and seventy six whole blood samples were analysed using two independent conventional and real time PCR assays to detect ASFV. Despite no recorded outbreak of clinical ASF during this time, virus was detected in 90/277 samples analysed by conventional PCR and 142/209 samples analysed by qPCR. Genotyping of a sub-set of these samples indicated that the viruses associated with the positive samples were classified within genotype IX and that these strains were therefore genetically similar to the virus associated with the 2006/2007 ASF outbreaks in Kenya.


CONCLUSIONS
The detection of ASFV viral DNA in a relatively high number of pigs delivered for slaughter during a period with no reported outbreaks provides support for two hypotheses, which are not mutually exclusive: (1) that virus prevalence may be over-estimated by slaughter-slab sampling, relative to that prevailing in the wider pig population; (2) that sub-clinical, chronically infected or recovered pigs may be responsible for persistence of the virus in endemic areas.
Centre for Infection Immunity, and Evolution, Institute for Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Ashworth Labs, West Mains Rd, Edinburgh, EH9 3JT, UK.|International Livestock Research Institute, PO Box 30709, Nairobi, 00100, Kenya.
Lian F
LF
Thomas
International Livestock Research Institute, PO Box 30709, Nairobi, 00100, Kenya.
Richard P
RP
Bishop
International Livestock Research Institute, PO Box 30709, Nairobi, 00100, Kenya.
Cynthia
C
Onzere
United States Department of Agriculture, Foreign Animal Disease Diagnostic Laboratory, National Veterinary Services Laboratories, Animal and Plant Health Inspection Services, PO Box 848, Greenport, NY, 1944, USA.
Michael T
MT
Mcintosh
United States Department of Agriculture, Foreign Animal Disease Diagnostic Laboratory, National Veterinary Services Laboratories, Animal and Plant Health Inspection Services, PO Box 848, Greenport, NY, 1944, USA.
Karissa A
KA
Lemire
Centre for Infection Immunity, and Evolution, Institute for Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Ashworth Labs, West Mains Rd, Edinburgh, EH9 3JT, UK.|International Livestock Research Institute, PO Box 30709, Nairobi, 00100, Kenya.
William A
WA
de Glanville
Centre for Infection Immunity, and Evolution, Institute for Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Ashworth Labs, West Mains Rd, Edinburgh, EH9 3JT, UK.|International Livestock Research Institute, PO Box 30709, Nairobi, 00100, Kenya.
E Anne J
EA
Cook
International Livestock Research Institute, PO Box 30709, Nairobi, 00100, Kenya. Eric.Fevre@liverpool.ac.uk.|Institute for Infection and Global Health, University of Liverpool, Leahurst Campus, Chester High Road, Neston, CH64 7TE, UK. Eric.Fevre@liverpool.ac.uk.
Eric M
EM
Fèvre
D000357:African Swine Fever / Q000097:blood / Q000453:epidemiology / Q000821:virology*; D000358:African Swine Fever Virus / Q000302:isolation & purification*; D000818:Animals; D004196:Disease Outbreaks / Q000662:veterinary; D005838:Genotype; D007630:Kenya / Q000453:epidemiology; D013552:Swine
ASFV real time PCR; African swine fever virus; Epidemiology; Genotype IX; Kenya; Slaughter house; p72 PCR