Abstract
In the absence of effective vaccine(s), control of African swine fever caused by African swine fever virus (ASFV) must be based on early, efficient, cost-effective detection and strict control and elimination strategies. For this purpose, we developed an indirect ELISA capable of detecting ASFV antibodies in either serum or oral fluid specimens. The recombinant protein used in the ELISA was selected by comparing the early serum antibody response of ASFV-infected pigs (NHV-p68 isolate) to three major recombinant polypeptides (p30, p54, p72) using a multiplex fluorescent microbead-based immunoassay (FMIA). Non-hazardous (non-infectious) antibody-positive serum for use as plate positive controls and for the calculation of sample-to-positive (S:P) ratios was produced by inoculating pigs with a replicon particle (RP) vaccine expressing the ASFV p30 gene. The optimized ELISA detected anti-p30 antibodies in serum and/or oral fluid samples from pigs inoculated with ASFV under experimental conditions beginning 8 to 12 days post inoculation. Tests on serum (n = 200) and oral fluid (n = 200) field samples from an ASFV-free population demonstrated that the assay was highly diagnostically specific. The convenience and diagnostic utility of oral fluid sampling combined with the flexibility to test either serum or oral fluid on the same platform suggests that this assay will be highly useful under the conditions for which OIE recommends ASFV antibody surveillance, i.e., in ASFV-endemic areas and for the detection of infections with ASFV isolates of low virulence.
Highlights
African swine fever (ASF) is a highly contagious disease of pigs caused by a large, icosahedral, enveloped, double-stranded DNA virus belonging to family Asfarvidiridae [1]
The reactivity of three major recombinant ASF virus (ASFV) antigens (p30, p72 and p54) was evaluated by testing serum samples collected between 0 and 26 day post inoculation (DPI) from 9 pigs inoculated with ASFV isolate NHV/P68 in the multiplex fluorescent microbead-based immunoassay (FMIA)
The response against p72 was slower than p30 and p54 responses, p72 FMIA responses at DPI 12 were significantly higher than DPI 0 (p = 0.0322), as were responses at DPI ! 14 (p < 0.0001)
Summary
African swine fever (ASF) is a highly contagious disease of pigs caused by a large, icosahedral, enveloped, double-stranded DNA virus belonging to family Asfarvidiridae [1]. Infection with ASF virus (ASFV) can produce clinical signs ranging from sudden death to subacute and chronic disease, depending on the virulence of the isolate, the affected host, dose and route of infection [3]. The expansion of ASFV within Africa and its introduction and spread across Transcaucasia, the Russian Federation, and Eastern Europe has heightened concerns for the emergence of the virus in ASFVfree countries either through infected free-ranging European wild boar (Sus scrofa), illegal imports of pork and other derived products or through contaminated fomites moving in global trade networks [5,6,7]. Surveillance programs in the Iberian Peninsula and Sardinia have used ASFV antibody detection in tandem with viral antigen detection, for the detection of ASFV carrier animals and elucidating the epidemiological characteristics of the epidemics, i.e., time since the virus introduction into a premises [4]
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