African swine fever virus (ASFV) is of concern to pork producers because of its high mortality rate, its severe economic impact, and its rapid geographic expansion in recent years. Prevention and control of ASFV is complicated by the absence of effective vaccines. Therefore, control is based on identification of infected animals and herds.
Detection of antibodies is useful for ASFV diagnosis and surveillance because antibodies are a definitive and reliable indication of infection (Sanchez-Vizcaíno et al., 2012). An earlier study showed that ASFV antibodies could be detected in oral fluids and suggested that oral fluids could serve as a suitable specimen for ASFV surveillance (Mur et al., 2013). The objective of NPB #13-048 was to develop a commercially-viable dual-matrix (serum or oral fluid) ASFV p30 antibody ELISA. The following steps were carried out:
1. The best recombinant antigen to use in the ELISA (p30) was selected by evaluating the serum antibody response of ASFV-infected pigs against 3 His-tagged fusion recombinant polypeptides (rp30, rp54, rp72) using a multiplex fluorescent microbead-based immunoassay (FMIA; Luminex® Corporation).
2. Serum and oral fluid antibody-positive samples were generated by experimental inoculation of 9 pigs with an attenuated ASFV isolate (NHV) that produces chronic infection. Paired oral fluid and serum samples were sequentially collected from individual pigs (DPI 0, 6, 12, 15, 19, 26, 33, 40, 47, 54, and 61). The specificity of the ELISA was evaluated using 200 serum and oral fluid samples submitted to the Iowa State University Veterinary Diagnostic Laboratory from swine herds in the U.S., i.e., a known ASFV-negative population.
3. The results of testing showed that IgG antibodies were detected by DPI 12 in both serum and oral fluid specimens. Evaluation of ASFV negative field samples showed ELISA specificities of 99.5% and 100% for serum and oral fluid samples, respectively.
4. Thus, the test detected ASFV antibodies in either oral fluid or serum samples early in the infection, yet was highly specific (few false positives) for both specimen types. Given the increased surveillance efficiency provided by oral fluid sampling and the ability to confirm results using serum samples, the ASFV rp30 antibody ELISA will be highly useful under conditions that require ASFV surveillance.