Purpose West Nile Virus (WNV) is a mosquito-born RNA virus first recognized in Uganda in 1937. It has since emerged as an increasing threat across the United States. There have been 15,824 reported cases in the U.S. with 619 human deaths. Human disease manifestations range from a mild febrile illness to severe neurological disease with meningitis or encephalitis. Studies focusing on survivors of WNV have shown persistence of immunoglobulin M (IgM) against WNV. This study investigates whether or not the persistence of IgM can be explained by persistent viremia. Persistent viremia, if present, would have implications for increased blood and organ donation transmission and may explain persistent disease symptoms.
Methods Patients identified by the NM State Laboratory with acute WNV infection as demonstrated by positive IgM in serum or cerebrospinal fluid with persistent symptoms after acute infection were eligible for the study. Convalescent immunoglobulin levels were measured with Enzyme-Linked Immunoabsorbant Assay. Peripheral blood mononuclear cells (PBMCs) and serum were collected from eleven patients with persistent or equivocal IgM levels. RNA was extracted from PBMCs and serum. Reverse transcriptase polymerase chain reaction (RT-PCR) using specific WNV primers is presently underway. Agarose gel electrophoresis will be performed to evaluate RT-PCR product and viral sequencing will be performed for confirmation.
Results Of the twenty-six WNV convalescent patients in the study, 23% remained IgM positive several months after initial diagnosis. An additional 19% of patients had equivocal IgM levels. All but two patients had persistence of IgG, one of which was equivocal.
Conclusion Nearly one-fourth of WNV patients with persistent symptoms months after acute infection have persistent IgM antibodies. RT-PCR presently underway will determine whether or not persistent viremia provides an explanation for persistent IgM levels. If RT-PCR indicates the presence of positive WNV RT-PCR products in PBMCs or serum of convalescent WNV patients, the natural history of the disease will be different than initially presumed, possibly increasing disease morbidity and increasing the transmission risk.