ASF outbreak investigations and sample collection
Between 2016 and 2018), 37 ASF outbreaks were reported in domestic pigs in 8 States of Nigeria (Fig 1). One hundred ten (110) outbreak samples were collected consisting of whole blood and tissue (liver, spleen, and lymph nodes) from 147 pig farms. The affected States were Abia, Benue, Enugu, Kaduna, Imo, Lagos, Plateau, and Taraba States (Fig. 1, Table 1). Samples were collected at intensive pig farms and free-roaming pigs in the affected States of the country. Laboratory diagnosis was carried at the ASF National Reference Laboratory (NRL) at the National Veterinary Research Institute (NVRI), Vom, Nigeria. Epidemiological investigations were carried out in all affected States. In 2016, ASF was reported in three States of Nigeria including: Benue, Kaduna, and Plateau States. One of the ASF outbreaks in Plateau State was reported in an institutional farm and the source of viral introduction was through farm workers. Three States (Abia, Imo, and Enugu) in Eastern Nigeria with contiguous common border reported ASF outbreaks in 2017. ASF outbreak in Imo State occurred due to the introduction of pigs from the Republic of Cameroon. The outbreak affected a cluster of seven intensive pig farms with a herd size of 60-1000 pigs and recorded mortality of 73% (2168/2930). A similar outbreak of ASF also occurred in neighbouring Abia State in a cluster of nine farms and a mortality rate of 80% (845/1050) was recorded in exotic breeds of pigs. The ASF outbreak started in one of the farms and it spread to other farms through the activities of butchers who also kept pigs. The ASF outbreak in Enugu State was also in an intensive small-holder pig farm. Similarly, ASF outbreaks were reported in 2018 in 3 Northern States (Benue, Taraba, and Plateau) with common boundaries (Fig 1). The outbreak started in Plateau State and was reported between April and November 2018 in small-holder intensive pig farms mostly in Jos-South Local Government Area (LGA) (Fig 1). Also in September 2018, the disease was reported in Zing, Taraba State, ASF affected 101 pig farmers with recorded mortality of 45.6% (3354/7360) pigs. Affected animals were mainly free-roaming Nigerian indigenous pig (NIP) breeds. In addition, widespread ASF outbreaks were reported in four major locations of Gboko, Otukpo, Yandev, and Makurdi, all in Benue State from June to December 2018. The affected pig farms were breeder and smallholder intensive farms. Lastly, in southwestern Nigeria, Lagos State recorded ASF outbreak close to the Nigeria-Benin republic international border in an intensive pig farm in 2018 with 75% (40/60) mortality.