Evaluation of an in-house indirect immunoperoxidase test (IPT) for African swine fever virus antibody detection

Authors: WU, PING - Animal And Plant Health Inspection Service (APHIS); MCDANIEL, ARIC - Animal And Plant Health Inspection Service (APHIS); RODRÍGUEZ, YELITZA - Animal And Plant Health Inspection Service (APHIS); BLAKEMORE, LESLIE - Animal And Plant Health Inspection Service (APHIS); SCHUMANN, KATE - Animal And Plant Health Inspection Service (APHIS); Chung, Chungwon; JIA, WEI - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: An in-house indirect immunoperoxidase test (IPT) for African Swine Fever (ASF) diagnosis was developed using MA-104 cells infected with ASF virus Georgia 2007/1 strain which is different from the reference IPT. The analytic sensitivity and specificity of the in-house IPT were found to be equivalent to the reference IPT. The diagnostic sensitivity and specificity of the in-house IPT were not statistically different from the reference IPT. However, with less tissue culture adaptation the in-house IPT can be potentially benefited by earlier detection of weak positive antibody. Field sample testing results by the in-house IPT and qPCR reflected the different statuses of ASF infection in a herd or an area. To ensure ASF diagnosis covers different field statuses of infection, it is essential to use both molecular and serological methods simultaneously.

Technical Abstract: African swine fever virus (ASFV) strains share common epitopes among their immunodominant viral proteins. ASFV-specific antibodies can be detected starting at 7-10 days post-infection and persist for months along with agent presentation, followed by a period in which only specific antibody may be detected in recovered and asymptomatically infected animals. Serodiagnosis is the only way to identify those recovered and asymptomatic animals. ELISAs for ASFV antibody detection are used for rapid screening of large numbers of animals with its high throughput capability. The OIE recommends that positive results by ELISA should always be confirmed with a second serological method such as an indirect immunoperoxidase test (IPT). Due to global supply issues of ASFV IPT kits, an in-house IPT for ASFV antibody detection was produced and evaluated. The analytic sensitivity and specificity of the in-house IPT was found to be equivalent to the reference IPT. The average positive agreement between the in-house IPT and the reference IPT was 95.45%, and the average negative agreement was 94.44%. The in-house IPT and a qPCR for molecular detection were used to test 1149 field samples. The results indicated that 242 samples were only positive by qPCR, 125 were positive by both qPCR and IPT, 23 were only positive by IPT, and 759 were negative by both IPT and qPCR. These results eventually reflected the different statuses of ASFV infection, which suggested that both molecular and serological tests were essential to reveal the statuses of ASFV infection in a herd.