Correlation between Indirect ELISA and Fluorescent Antibody Virus Neutralization Test for Evaluating Vaccine-Induced Immune Responses Against Classical Swine Fever in India
Akshatha Velankar
ICAR-National Institute of Veterinary Epidemiology and Disease Informatics (NIVEDI), Bengaluru, India.
Pavithra Narendran
The University of Trans- Disciplinary Health Sciences and Technology (TDU), Bengaluru, India.
B. M. Chandranaik
Institute of Animal Health and Veterinary Biologicals (IAH&VB), Bengaluru, India.
Kuralayanapalya Puttahonnappa Suresh
ICAR-National Institute of Veterinary Epidemiology and Disease Informatics (NIVEDI), Bengaluru, India.
Sharanagouda Shiddanagouda Patil *
ICAR-National Institute of Veterinary Epidemiology and Disease Informatics (NIVEDI), Bengaluru, India.
*Author to whom correspondence should be addressed.
Abstract
Protective antibody responses against Classical Swine Fever Virus (CSFV) are an important indicator for monitoring vaccine-induced immunity in pigs. This study evaluated the correlation between indirect ELISA (iELISA) and fluorescent antibody virus neutralization test (FAVNT) for assessing neutralizing antibody responses in vaccinated pigs using 846 post-vaccination serum samples. Antibody detection was performed using both assays, and their relationship was assessed through Pearson’s correlation analysis, while diagnostic performance of iELISA was evaluated using FAVNT as the reference assay by calculating sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), Cohen’s kappa coefficient, and receiver operating characteristic (ROC) curve analysis. The iELISA demonstrated a sensitivity of 94.0% and specificity of 100%, with PPV and NPV of 100% and 88.3%, respectively. A strong agreement was observed between the two assays (κ = 0.91), and correlation analysis revealed a significant positive association between iELISA optical density values and FAVNT neutralizing antibody titres (r = 0.86, P < .001). ROC analysis showed excellent diagnostic accuracy with an area under the curve (AUC) of 0.981 for predicting protective neutralizing antibody titres (≥1:32). The majority of vaccinated pigs exhibited protective neutralizing antibody responses, indicating effective post-vaccination immunity. These findings suggest that iELISA can serve as a reliable, rapid, and high-throughput surrogate assay for large-scale serological monitoring of vaccine-induced immunity against CSFV, while FAVNT remains valuable for confirmatory testing and detailed immunological evaluation.
Keywords: Classical swine fever virus, iELISA, FAVNT, serological monitoring, neutralizing antibodies