
African swine fever (ASF) is a severe haemorrhagic infectious disease affecting suids, thus representing a great economic concern. The disease is caused by a large and complex double-stranded DNA virus (genus Asfivirus, family Asfarviridae). Many epidemics occurred along the last century, from the first records in Kenya (1907), Sardinia (1978-current), until the recent outbreak from Eastern to Central and Southern Europe. Considering the importance of the early diagnosis, rapid point of care testing (POCT) for ASF is highly demanded. In this work, we developed two strategies for the rapid and onsite diagnosis of ASF, based on Lateral Flow Immunoassay (LFIA) and Recombinase Polymerase Amplification (RPA) techniques. The first one based on sandwich-type LFIA exploiting a monoclonal antibody directed to the p30 protein of the virus (Mab). ASFV protein is captured by Mab anchored onto LFIA membrane and a secondary antibody detect Mab-p30 complex, if formed. The initial use of the same antibody for protein capture and complex detection showed a significant competitive effect for antigen binding. To solve this problem, minimizing reciprocal interference and maximizing the response, an experimental design was applied. This approach allowed us to develop the most sensitive test achievable with the available materials. The second one, based on RPA assay, requested the employment of primers to the capsid protein p72 gene, an exonuclease III probe and was performed at 39 ◦C. Using a plasmid encoding target gene a limit of detection of 5 copy/μL was achieved. The devloped LFIA and RPA were applied for ASFV detection in the usually analysed animal tissues such as kidney, spleen, and lymph nodes. For sample preparation we used a simple and universal virus extraction protocol, followed by DNA extraction and purification for the RPA. Regarding LFIA, the on-field addition of 3% H2O2 is sufficient to limit matrix interference and prevent false positive results. The two rapid methods are performable in just 25 min (RPA) and 15 min (LFIA). An high diagnostic specificity (100%) and sensitivity (93% and 87% for LFIA and RPA, respectively) was obtained for samples with high viral load (Ct 28) and/or also containing specific antibodies to ASFV, which decreased antigen availability and were indicative of a chronic and poorly transmissible infection. The simple and rapid sample preparation and the diagnostic performance of the LFIA are key points to suggest its large applicability for POC diagnosis of ASF.
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