Data collection: Data was collected based on key informant interviews of government and pig traders’ union officials at the market sites. Data collected were: average weekly population of pigs in the markets. Towns and villages from where pigs are brought into the markets and locations where the pig purchased are transported to. Government regulations in the markets and attached slaughter slabs and the fate of pigs unsold on at the market. Data on the average number of pigs slaughtered at the slabs were also collected.
Field observation: Due to poor records at the selected LPMs, observations of activities of the value chain actors (traders, farmers, transporters) and slaughter slab operators were carried out using a checklist. These include pre-entry inspections of pigs going in and out of the market site, mode of transportation of the pigs, holding facilities at the markets e.g pens, activities of the slaughter slab operators, and access of people and other animals to the market sites. Others include common breeds of pigs at the market, estimated age of pigs brought to the market, sanitation, and hygiene at the market sites. To carry out this aspect of the study, arrival at market sites was from 7 am to 8 am depending on location to maximize observation of activities, sample collections, and travel time back to the laboratory. At least 2 cycles of visits were planned per month for data and sample collection.
Figure 1 : Map of Northern part of Nigeria, showing the movement of pigs from towns and villages into the four selected live pigs markets
Figure 2 : Map of Nigeria showing movement and outflows of pigs from four selected pig markets to various destinations in the country
Sample size determination and collections: From April 2019- Feb 2020, October-November, 2020 samples were collected at the Dawaki, Katsit, Numan, and Pandam pig markets in Nigeria. With a population of 7million pigs, the minimum recommended sample size for such a population using a confidence level of 95% and a margin of error of 5% gives a calculated sample size of 384 (Dohoo et al., 2009). The samples were collected using a convenient sampling method, based on the cooperation of the pig traders and slaughter slab operators. The samples collected were whole blood, tissue, and sera samples. 5mls of blood in heparinized and plain sample bottles were collected from pigs at LPMs and their slaughter slabs. Tissue samples (liver, spleen, and mesenteric nodes) were collected in labelled sample bottles from all pigs slaughtered at the slaughter slabs within the premises of the LPMs. Criteria for sample collection at the slaughter slab was pigs bought at LPMs, pigs from external sources were excluded. Both apparently healthy and sick pigs were sampled. Sample collection was disrupted between March 2020 and September 2020 due to COVID-19 lockdown restrictions in Nigeria.
Detection of African swine fever antibodies : Sera samples collected were analyzed using commercially available ID Screen ASF Indirect kit (IDVet, Grabels, France) specific for the presence of antibodies against ASFV p32, p62 , and p72 proteins according to the manufacturer´s instructions.
Detection of African swine fever virus. Total DNA was extracted from whole blood and homogenized tissue samples using the Qiagen Mini kit (Qiagen, Hilden Germany) following the manufacturer’s protocol. A 257 bp region corresponding to the C-terminal region of the B646gene encoding the p72 major capsid protein was amplified using the diagnostic primers PPA1 and PPA2 as previously reported to confirm the presence of the ASFV genome (Aguero et al., 2003).