Human Orthopoxvirus Infection Detected by Igm ELISA Kevin L

Human Orthopoxvirus infection detected by IgM ELISA

Kevin L. Karem, Mary Reynolds, Zach Braden, Gin Lou, Nikeva Bernard, Joanne Patton, Inger K. Damon. Poxvirus Program, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta Ga.

Abstract. In 2003, monkeypox outbreaks were identified in the United States as well as simultaneously in the Republic of Congo. Patients’ sera were sent to the Centers for

Disease Control and Prevention as a part of outbreak response measures. Clinical and epidemiologic information was abstracted from the case investigation forms. Serum samples from patients were tested using an IgM capture and an IgG ELISA against orthopoxvirus antigen. Patients were classified as confirmed, probable or suspect cases, or were excluded as cases based on laboratory test results, epidemiologic, and clinical criteria. Patient IgM serologic testing was used as diagnostic support for acute infection, but was not considered as a stand alone diagnostic assay. Retrospective analysis indicates that the IgM ELISA provided up to 95% specificity and 95% sensitivity for diagnosing acute monkeypox infection when compared to conformation using molecular or other virologic testing (Karem et al. 2005 CDLI 12:867-72). Analysis of paired sera detected sero-conversion for both IgM and IgG, providing another indicator of recent infection. In addition, the detection of IgM in previously vaccinated (smallpox vaccine) monkeypox cases provides evidence for the use of the assay in vaccinated populations exposed to heterologous poxviruses. This may include exposure to monkeypox, variola or other non-vaccinia poxviruses. Application of the assay and implications for diagnostic testing are discussed.