Active Surveillance and Farm-Level Risk Evaluation of African Swine Fever in Southern Nigeria.

Pig farms in Southern Nigeria face recurrent threats from enzootic viral infections, yet active surveillance remains limited. This study implemented an active surveillance approach targeting African swine fever virus (ASFV) to assess its circulation across four states. We sampled 40 pig farms and two abattoirs, collecting swine blood and ticks for molecular and serological analysis. Sampling was conducted during both African swine fever (ASF) outbreak (n = 27 pigs) and non-outbreak (n = 204 pigs) periods, resulting in 231 samples tested for ASFV DNA. Additionally, 46 plasma samples from the non-outbreak period were screened for ASFV-specific antibodies. ASFV was detected in all pigs sampled during outbreak periods (27/27; 100%), whereas none of the pigs sampled during non-outbreak periods tested positive (0/204). Of the 27 positives, sequencing generated 7 genomes characterized as genotype II. Serological testing of the 46 plasma samples from non-outbreak pigs revealed no ASFV seropositivity. All tick samples were negative for ASFV DNA. Farm-level risk evaluations revealed widespread biosecurity lapses, suggesting these deficiencies as potential drivers of ASFV circulation. These findings underscore the urgent need to strengthen farm-level biosecurity and demonstrate the pivotal role of active surveillance and genome sequencing in detecting and characterizing ASF outbreaks.