Comparison of PCR methods for detection of classical swine fever virus and other pestiviruses

Evaluation of antibody and antigen cross-reaction in Kenyan dairy cattle naturally infected with two pestiviruses: Bovine viral diarrhea virus and classical swine fever virus

Background and Aim:

Bovine viral diarrhea virus (BVDV) and classical swine fever virus (CSFV) are important pathogens of cattle and pigs, respectively, and belong to the genus Pestivirus. As CSFV has been shown to infect cattle, it can create diagnostic challenges of BVDV results through possible cross-reactivity where cattle could be exposed to pigs and CSFV. This study aimed to determine the possible cross-reactivity of BVDV and CSFV enzyme-linked immunosorbent assay (ELISA) results for antigen (Ag) and antibody (Ab) among smallholder dairy cattle in Kenya.

Materials and Methods:

This was a cross-sectional study based on a single visit to farms to collect serum samples and other descriptive farm-level and animal-level information. Testing for BVDV Ag and Ab was conducted on serum samples from 320 dairy cows and heifers, with CSFV Ag and Ab testing conducted on a subset of 133 and 74 serum samples, respectively. CSFV testing was based on BVDV test results and the availability of enough sample volume from farms that kept pigs. The Ag and Ab tests utilized IDEXX ELISA for both BVDV and CSFV.

Results:

For the 74 samples with Ab tests for both viruses, 40 (54.0%) were BVDV Ab positive, while 63 (85.1%) were CSFV Ab positive. Of the 40 BVDV Ab positive samples, 36 cattle (90.0%) tested positive for CSFV Ab. However, of the 34 BVDV Ab negative samples, 27 (79.4%) were CSFV Ab test-positive. For the 133 samples with Ag tests for both viruses, 125 (94.0%) were BVDV Ag positive, while 2 (1.5%) samples were CSFV Ag positive. None of the eight BVDV Ag negative samples was positive for CSFV Ag and only two (1.6%) of the 125 BVDV Ag positive samples were positive for CSFV Ag.

Conclusion:

The results indicate either substantial cross-reactivity of the two Ab ELISA tests, or reactivity with some other protein in the samples that led to the positive Ab test results. There was only limited evidence for cross-reactivity of the two Ag ELISA tests. We recommend that Pestivirus genus cross-reactivity be considered when interpreting BVDV ELISA results in cattle, more for Ab than Ag tests. Further research is needed to clarify the levels of cross-reactivity between BVDV and other Pestivirus Ag and Ab tests from animals on mixed-species farms.

Seroprevalence of Classical Swine Fever in pigs of Karnataka and comparative diagnostic evaluation of antigen ELISA and reverse transcriptase -PCR

Classical swine fever is highly contagious viral disease of swine causing huge economic losses to pig farmersand pig industry. The study was conducted in Karnataka to understand the current scenario of CSF in the state andto evaluate efficiency of diagnostic tests (antigen ELISA and RT-PCR) in detecting the disease. Serum sampleswere collected from 270 pigs from 13 districts of the state and were tested for the presence of CSF antibodies.Whole blood samples (151) from 14 outbreaks of CSF were collected for the comparative diagnosis of the diseaseusing Antigen ELISA and reverse transcriptase (RT)-PCR. A seroprevalence of 28.5% (77/270) was found in theserum samples collected form the whole Karnataka. The southern Karnataka had higher seroprevalence (47%) incomparison to northern Karnataka region where seroprevalence was 17%. It confirms endemicity of the disease insouthern region. Of 151 blood samples collected for comparative diagnosis, 61 samples were positive for CSF byRT-PCR and 39 by antigen ELISA, indicating the superiority of RT-PCR over antigen ELISA to detect CSFVinfection in earliest stages of infection.