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

Erika Chenais,Erika Chenais,Lihong Liu,Susanna Sternberg-Lewerin,Charles Masembe,Neil Leblanc,Sofia Boqvist,Tonny Aliro,Karl Ståhl,Karl Ståhl

doi:10.1007/s11250-016-1197-0

Abstract

In Uganda, a low-income country in east Africa, African swine fever (ASF) is endemic with yearly outbreaks. In the prevailing smallholder subsistence farming systems, farm biosecurity is largely non-existent. Outbreaks of ASF, particularly in smallholder farms, often go unreported, creating significant epidemiological knowledge gaps. The continuous circulation of ASF in smallholder settings also creates biosecurity challenges for larger farms. In this study, an on-going outbreak of ASF in an endemic area was investigated on farm level, including analyses of on-farm environmental virus contamination. The study was carried out on a medium-sized pig farm with 35 adult pigs and 103 piglets or growers at the onset of the outbreak. Within 3 months, all pigs had died or were slaughtered. The study included interviews with farm representatives as well as biological and environmental sampling. ASF was confirmed by the presence of ASF virus (ASFV) genomic material in biological (blood, serum) and environmental (soil, water, feed, manure) samples by real-time PCR. The ASFV-positive biological samples confirmed the clinical assessment and were consistent with known virus characteristics. Most environmental samples were found to be positive. Assessment of farm biosecurity, interviews, and the results from the biological and environmental samples revealed that breaches and non-compliance with biosecurity protocols most likely led to the introduction and within-farm spread of the virus. The information derived from this study provides valuable insight regarding the implementation of biosecurity measures, particularly in endemic areas.

Highlights

African swine fever (ASF) was first observed and described in pigs of European settlers (Sus scrofa) in Kenya in the beginning of the twentieth century (Montgomery 1921)
The information derived from this study provides valuable insight regarding the implementation of biosecurity measures, in endemic areas
ASF is a contagious, typically lethal, hemorrhagic disease of domestic pigs caused by a double-stranded DNA virus, the sole member within the Asfarviridae family, genus Asfivirus (Plowright et al 1994)

Summary

Introduction

African swine fever (ASF) was first observed and described in pigs of European settlers (Sus scrofa) in Kenya in the beginning of the twentieth century (Montgomery 1921). The epidemiology is complex with a sylvatic cycle involving asymptomatically infected warthogs and soft ticks, a domestic cycle involving soft ticks and domestic pigs, and an additional domestic cycle with pig-to-pig transmission (Costard et al 2013; Jori et al 2013). The latter transmission cycle has been identified as the main driver of disease in areas with a high density of pigs, mainly free-range systems, and a low level of farm biosecurity such as in sub-Saharan Africa (Penrith et al 2013). ASF has severe economic impacts, both in high- and lowincome countries (Sanchez-Vizcaino et al 2013; Mur et al 2014; Chenais et al 2015a), and its control is essential for

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