Semi-quantitative risk evaluation reveals drivers of African swine fever virus in smallholder pig farms and gaps in biosecurity, Tanzania

Abstract African swine fever (ASF) has remained persistent in Tanzania since the early 2000. Between 2020 and 2021, twelve districts in Tanzania were infected with ASF, and ≥ 4,804 pigs reportedly died directly due to the disease with disruption to livelihoods. We conducted semi-quantitative field investigations and rapid risk assessment (RRA) to understand the risk factors and drivers of ASF virus (ASFv) amplification and transmission in smallholder pig farms, and determine the gaps in biosecurity through hazard profiling, focused group discussions and experts’ opinions. Outbreaks were connected by road and aligned along the pig product value chain and reported in the northern, central and southern parts of Tanzania. The patterns of outbreaks and impacts differed among districts, but cases of ASF appeared to be self-limiting following significant mortality of pigs in farms. Movement of infected pigs, movement of contaminated pig products and fomites associated with service providers, vehicles, and equipment, as well as the inadvertent risks associated with movements of animal health practitioners, visitors and scavengers were the riskiest pathways to introduce ASFv into smallholder pig farms. Identified drivers and facilitators of risk of ASFv infection in smallholder pig farms were traders in whole pigs, middlemen, pig farmers, transporters, unauthorized animal health service providers and the traders in pork. All identified pig groups were susceptible to ASFv, particularly among shared adult boars, pregnant and lactating sows and adult female. The risk of ASF for smallholder pig farms in Tanzania remains very high based on a systematic risk classification. Majority of the farms poorly implemented biosecurity and no single farm implemented all the identified biosecurity measures. Risky practices and breach of biosecurity in the pig value chain in Tanzania are profit-driven and are extremely difficult to change. Behavioural change communication must target identified drivers of infections, attitudes and practices.