A longitudinal survey of African swine fever in Uganda reveals high apparent disease incidence rates in domestic pigs, but absence of detectable persistent virus infections in blood and serum

Abstract

BackgroundAfrican swine fever (ASF) is a fatal, haemorrhagic disease of domestic pigs, that poses a serious threat to pig farmers and is currently endemic in domestic pigs in most of sub-Saharan Africa. To obtain insight into the factors related to ASF outbreaks at the farm-level, a longitudinal study was performed in one of the major pig producing areas in central Uganda. Potential risk factors associated with outbreaks of ASF were investigated including the possible presence of apparently healthy ASF-virus (ASFV) infected pigs, which could act as long-term carriers of the virus. Blood and serum were sampled from 715 pigs (241 farms) and 649 pigs (233 farms) to investigate presence of ASFV and antibodies, during the periods of June-October 2010 and March-June 2011, respectively. To determine the potential contribution of different risks to ASF spread, a questionnaire-based survey was administered to farmers to assess the association between ASF outbreaks during the study period and the risk factors.ResultsFifty-one (21 %) and 13 (5.6 %) farms reported an ASF outbreak on their farms in the previous one to two years and during the study period, respectively. The incidence rate for ASF prior to the study period was estimated at 14.1 per 100 pig farm-years and 5.6 per 100 pig farm-years during the study. Three pigs tested positive for ASFV using real-time PCR, but none tested positive for ASFV specific antibodies using two different commercial ELISA tests.ConclusionsThere was no evidence for existence of pigs that were long-term carriers for the virus based on the analysis of blood and serum as there were no seropositive pigs and the only three ASFV DNA positive pigs were acutely infected and were linked to outbreaks reported by farmers during the study. Potential ASF risk factors were present on both small and medium-scale pig farms, although small scale farms exhibited a higher proportion with multiple potential risk factors (like borrowing boars for sows mating, buying replacement from neighboring farms without ascertaining health status, etc) and did not implement any biosecurity measures. However, no risk factors were significantly associated with ASF reports during the study.

Enhancing knowledge and awareness of biosecurity practices for control of African swine fever among smallholder pig farmers in four districts along the Kenya–Uganda border

“…This was in agreement with results obtained earlier in Uganda (Chenais et al 2015; Muhangi et al 2015). However, a caveat was that farmers appeared to assume that any disease that killed pigs was ASF, suggesting that 'ground truthing' using validated diagnostic tests was required to validate prevalence estimates based solely on feedback from farmers.…”

“…On this continent, the sector is currently dominated by small-scale free-range pig production systems, characterized by minimum investment in feed and housing. There are low levels of biosecurity in the smallholder pig production in Uganda (Muhangi et al 2015) resulting in pigs being exposed to diseases. It is widely believed that the major disease constraint to development of the pig sector in Africa is African swine fever (ASF) the most important transboundary animal disease of pigs globally.…”

“…Pig farming is an attractive venture for smallholder farmers because of the pig's ability to convert agro-industrial by-products and household waste into quality animal protein, combined with the short-production cycle of pigs and their high fecundity. As a result, the importance of pigs as a source of food and income generation is growing fast, as reflected in the dynamics of the pig sector in Africa (Muhangi et al 2015). On this continent, the sector is currently dominated by small-scale free-range pig production systems, characterized by minimum investment in feed and housing.…”

“…There has been a rapid increase in the production and consumption of pork over the past 5 years in some countries in sub-Saharan Africa (FAO 2011;Muhangi et al 2015). Pig farming is an attractive venture for smallholder farmers because of the pig's ability to convert agro-industrial by-products and household waste into quality animal protein, combined with the short-production cycle of pigs and their high fecundity.…”

African swine fever outbreak on a medium-sized farm in Uganda: biosecurity breaches and within-farm virus contamination

“…The presence of ASFV in the sylvatic cycle is probably as ancient as in other areas of the region (Montgomery 1921; Plowright et al 1994), but with a growing domestic pig population, numerous outbreaks are now described every year (Gallardo et al 2011; Muwonge et al 2012; Atuhaire et al 2013; Barongo et al 2015; Chenais et al 2015b; Muhangi et al 2015). The Ugandan pig population is the largest in East Africa (FAOSTAT 2013), but larger-scale enterprises are rare and most of the pigs are still kept in smallholder family farms in the rural areas (NEPAD and FAO 2004; Dione et al 2014).…”