Detection of eastern equine encephalomyelitis virus and Highlands J virus antigens within mosquito pools by enzyme immunoassay (EIA). II. Retrospective field test of the EIA.

This research compares the accuracy and effectiveness of using a test called an enzyme immunoassay (EIA) to detect two types of mosquito-borne viruses, eastern equine encephalomyelitis and Highlands J, against traditional methods. While the EIA showed high accuracy, especially with highly concentrated virus samples, it was less successful with low-concentration samples, suggesting it is a promising method for monitoring mosquito populations for these viruses.

Introduction and Methodology

• The researchers aimed to test the performance of Enzyme Immunoassays (EIAs) for detecting eastern equine encephalomyelitis (EEE) and Highlands J (HJ) virus antigens in mosquito samples against the traditional virus isolation procedures (VIP).
• The study was a retrospective one, referencing results from the original VIP tests that were carried out between 1979 and 1981.
• The standard VIP used for comparison was a plaque assay in chick embryo cell culture.

Results and findings

• Generally, the EIA showed a sensitivity rate of 0.7674 and a false negative rate of 0.2326 when compared to the original VIP.
• However, the sensitivity of the EIA increased when considering the storage age and initial level of virus titer in each sample.
• Samples that originally had over 1,500 plaque-forming units (PFU) per ml showed a considerably increased EIA sensitivity at a rate of 0.97.
• However, the sensitivity rate fell to 0.14 for samples with less than 500 PFU per ml originally, with 68% of false negatives occurring in these lower-titer sample pools.
• The researchers speculated that the low quantities of virus in those negative-result pools may have been lost during storage and handling processes. In fact, only 16% of these samples produced virus during attempts to reisolate using BHK-21 cells.
• The EIA proved highly specific and showed no false positives. Over 98% of the time, the EIA’s serological identity matches were identical to those determined by plaque reduction neutralization.

Conclusion

• The researchers concluded that factors such as pool size, species of mosquitoes or gravidity did not impact EIA results.
• The research supports using EIAs in surveillance programs to determine infection rates of known arboviruses in vector populations due to their high specificity and sensitivity rates, particularly for high-titer samples.