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

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.

Keywords: Environmental contamination; Environmental sampling; Farm biosecurity; Infectious disease outbreak; Smallholders.

Fig. 1

Approximate plan of the study farm indicating sites where environmental samples were taken during a confirmed African swine fever outbreak in a medium-sized farm in Lira district, Uganda. Lettered squares mark the different buildings, light gray areas indicate sites used for placing carcasses awaiting burial, and burial of carcasses, and dark gray areas mark sites used for bleeding pigs at slaughter. The dotted area outlines the overflow from a septic tank. Numbers mark environmental samples (1–35) taken on the 2nd of April 2014. Compound size: around 40 × 60 m. A latrines; B septic tanks; C concrete pig stables, 10 pens; D wood fence pig stables, 3 pens; E first slaughter place, wood structure; F latter slaughter place, concrete slab; G offices and storage

Fig. 2

Accumulated number of dead and slaughtered pigs during a confirmed African swine fever outbreak in a medium-sized farm in Lira district, Uganda