Serologic diagnosis of West Nile and St. Louis encephalitis virus infections in domestic chickens.

Adult domestic chickens were infected with West Nile virus (WNV) or St. Louis encephalitis virus (SLEV) and challenged with homologous or heterologous virus at 21 or 56 days postinfection (dpi). Sera were collected at selected time points after infection and assayed by enzyme immunoassay (EIA), plaque reduction neutralization test (PRNT), and a Western blot (WB) alternative to PRNT. EIA results were sensitive and accurate (few false positives) but not specific, requiring a confirmatory test to determine virus infection history. PRNT results generally were specific until challenge, after which test results were frequently equivocal and inadequate to determine first or second infecting virus. WB results confirmed the serologic cross-reactivity between WNV and SLEV envelope protein. Non-structural protein 1 and pre-membrane protein reactivities were highly specific for WNV during SLEV infection, but less specific for SLEV during WNV infection. WB and PRNT specificities were similar for both viruses from 6 to 14 dpi, and sensitivities to WNV were virtually identical.

Flavivirus serology by Western blot analysis.

The spread of West Nile virus (WNV) across the United States into areas with endemic flavivirus activity has complicated serologic surveillance of seasonal virus activity and diagnosis of infected individuals. Here we describe preliminary results from a comparison of serologic assays for flaviviruses: the reference plaque reduction neutralization test (PRNT), enzyme immunoassay (EIA), and a Western blot (WB) in which crude viral lysates were electrophoresed and blotted onto nitrocellulose. Human and chicken sera were tested and compared by each method against WNV and St. Louis encephalitis virus (SLEV). Antibody binding to three viral proteins determined WB interpretation: non-structural protein 1 (NS1), envelope (E), and pre-membrane (prM). WB results for a group of serially collected human plasma samples from WNV seroconverting blood donors were also correlated with transcription mediated amplification (TMA) and polymerase chain reaction (RT-PCR) results. Reactivity with NS1 appeared to be the most useful differentiating marker of WNV and SLEV infection in humans and chickens. Envelope protein was highly cross-reactive and, as indicated by additional results from dengue virus (DENV)-positive human sera, is perhaps useful serologically as a flavivirus group antigen.

Maternal HIV-1 antibody and vertical transmission in subtype C virus infection.

The role of maternal humoral immune response and viral load was analyzed in relation to the incidence of mother-to-child transmission (MTCT) of infants born to HIV-1 subtype C infected mothers. High levels of viral RNA in the serum correlated with MTCT as did high titers of subtype C consensus V3 peptide binding antibodies (BA) and neutralizing antibody (NA) to subtype B HIV-1MN. Logistic regression analysis showed that maternal viral load and V3 peptide subtype C BA were independent predictors for MTCT, odds ratio (OR) = 2.22 and OR = 2.52, respectively. No correlation between NA to homologous HIV-1 subtype C virus and MTCT was found. BA to V3 peptides may provide a rapid inexpensive method that can be used to determine the risk of HIV-1 MTCT.