Introduction
African swine fever (ASF) is caused by African swine fever virus (ASFV), a large double-stranded DNA virus, and the sole member of the genusAsfivirus within the Asfarviridae family (Alonso et al., 2018). African swine fever usually causes an exceptionally high lethality in domestic pigs and Eurasian wild boar and is a notifiable disease according to the World Organization for Animal Health (OIE). Following its introduction to Georgia in 2007, ASFV spread successively through neighboring countries in the Trans-Caucasian region to several parts of Europe and Asia (Dixon, Stahl, Jori, Vial, & Pfeiffer, 2020). Since the virus reached China in 2018 (Zhou et al., 2018), millions of pigs were culled and effects on the global pork market were severe. First cases of ASF in Germany in 2020 (Sauter-Louis et al., 2020) sent another shockwave through the industry, as trade restrictions on pork took hold even as only wild boar are affected until now. With neither treatment nor a licensed vaccine available to date, strategies to fight the disease have to rely solely on strict sanitary measures, an early and effective diagnosis and the culling of affected herds (Blome, Franzke, & Beer, 2020). For the wild boar situation, fencing, adapted hunting and hunting rest practices, trapping, incentives for carcass search and removal, as well as a general reduction of the wild boar populations have been implemented (Busch et al., 2021; Chenais et al., 2019; EFSA et al., 2018).
The OIE lists conventional and real-time PCR assays, virus isolation and fluorescent antibody tests as proven and reliable diagnostic methods for the detection of virus genome or antigen (OIE, 2019). However, these methods are rather time consuming and require laboratory conditions.
During its spread through Europe and Asia, ASF has affected countries with scarce infrastructure and limited laboratory capacities. Even if routine laboratory diagnosis is established, infected wild boar could succumb in remote forest areas, far from centralized testing facilities. With the effectiveness of disease control measures relying on a timely implementation after an outbreak (Sanchez-Vizcaino, Mur, & Martinez-Lopez, 2012) and laboratory analysis being rather cost-intensive, questions upon the utility point-of-care (POC) assays, possibly even to replace laboratory testing, have arisen. Epidemiological investigations can also benefit from the availability of an effective POC test, e.g. when culling measures take hold in an outbreak scenario and the status of individual animals or farms is of scientific interest for back tracing of transmission factors. The INGEZIM ASFV CROM Ag LFA (Sastre et al., 2016) commercialized by Eurofins Technologies Ingenasa is designed for the diagnosis of ASFV antigen in blood under field conditions, possibly suiting these scenarios.
Rather promising results were obtained in previous studies under laboratory conditions and when sample quality was ideal or close to ideal (Pikalo et al., 2021; Pikalo et al., 2020). Here, we aimed to assess the applicability under field conditions with a total of 237 blood samples of different origins. These investigations complement the previous studies on the lateral flow assay with a practice-orientated approach, simulating the possible application as POC test for antigen detection in carcasses when possible effects of decomposition have occurred. The results of the antigen LFA were compared to OIE listed qPCR diagnosis, and the resulting sensitivity and specificity were evaluated for assessment of the practicability of the on-site test under realistic conditions with real field samples.