Lateral flow assays for the detection of African swine fever virus antigen are not fit for field diagnosis of wild boar carcasses

Abstract

African swine fever (ASF) is one of the most important viral diseases of domestic pigs and wild boar. Apart from endemic cycles in Africa, ASF is now continuously spreading in Europe and Asia. As ASF leads to severe but unspecific clinical signs and high lethality, early pathogen detection is of utmost importance. Recently, “point-of-care” (POC) tests have been intensively discussed for the use in remote areas but also in the context of on-farm epidemiological investigations and wild boar carcass screening. Along these lines, the INGEZIM ASFV CROM Ag lateral flow assay (Eurofins Technologies Ingenasa) promises virus antigen detection under field conditions within minutes. In the present study, we evaluated the performance of the assay with selected high-quality reference blood samples, and also with real field samples from wild boar carcasses in different stages of decay from the ongoing ASF outbreak in Germany. While we observed a sensitivity of roughly 77% in freeze-thawed matrices of close to ideal quality, our approach to simulate field conditions in direct carcass testing without any modification resulted in a drastically reduced sensitivity of only 12.5%. Freeze thawing increased the sensitivity to roughly 44% which mirrored the overall sensitivity of 49% in the total data set of carcass samples. A diagnostic specificity of 100% was observed. However, most of the German ASF cases in wild boar would have been missed using the lateral flow assay (LFA) alone. Therefore, the antigen-specific LFA should not be regarded as a substitute for any OIE listed diagnostic method and has very limited use for carcass testing at the point of care. For optimized LFA antigen tests, the sensitivity with field samples must be significantly increased. An improved sensitivity is seen with freeze-thawed samples, which may indicate problems in the accessibility of ASFV antigen.

A practical guide for strategic and efficient sampling in African swine fever‐affected pig farms

“…These field results are in line with experimental studies (Pikalo et al., 2021). A recent study found a high positivity rate for Ag‐LFD during the acute phase of disease between days 4 and 7 post‐infection (dpi) when testing EDTA‐blood as sample matrix or up to 10 days when serum is used as the sample matrix (Deutschmann et al., 2022; Pikalo et al., 2021). Therefore, it should be kept in mind that the sensitivity of Ag‐LFD limits its use to acutely sick animals 4–10 dpi.…”