Assessment of residual African swine fever virus DNA presence on pig farm surfaces following outbreaks in Busukuma and Nakawa divisions

Abstract

African swine fever (ASF), caused by the African swine fever virus (ASFV), remains a major constraint to pig production in Uganda. ASFV DNA can remain detectable on farm surfaces after infected pigs are removed. However, field-based information on the persistence of the viral DNA in endemic settings following real outbreaks is limited. This study assessed the presence of residual ASFV DNA on farm surfaces and fomites following routine post outbreak cleaning practices. A cross-sectional study design was employed, covering five purposively selected pig farms in Busukuma and Nakawa Divisions in Wakiso and Kampala districts, respectively. Structured questionnaires were administered to capture farm characteristics and post-outbreak cleaning practices. One swab sample was collected from each of six targeted surfaces and fomites per farm (pen floors, pen walls, feeders, water troughs, cleaning tools, and footwear), giving 30 samples in total. DNA was extracted from all the samples and screened using conventional polymerase chain reaction (PCR) targeting the p72 gene. All 30 samples tested negative for ASFV DNA, despite variation in herd size, cleaning practices, and time since the last sick pig was removed. These findings suggest that ASFV DNA on farm surfaces is unlikely to be detected at post-outbreak intervals of three to nine weeks in comparable settings. The study recommends a fallow period of four to nine weeks before restocking, and calls for longitudinal studies to separate the effects of cleaning from natural environmental decay.

Keywords: African swine fever virus (ASFV); environmental persistence; polymerase chain reaction (PCR); post-outbreak cleaning; Uganda