The research also sheds new light on the 2003 monkeypox outbreak in the Midwest - monkeypox is closely related to smallpox. This new information suggests that the 2003 outbreak was larger than the 72 cases reported by the Centers for Disease Control and Prevention (CDC). The research was released online this week by the medical journal Nature Medicine. The study will also appear in the September 2005 print edition of the journal.
"The 2003 outbreak of monkeypox provided some incredibly valuable information about the country's level of preparedness for an infectious disease outbreak that is either naturally occurring or an act of terrorism," said Mark Slifka, Ph.D., lead author and an assistant scientist at the VGTI, an assistant professor of molecular microbiology and immunology in the OHSU School of Medicine and an assistant scientist at the Oregon National Primate Research Center. "Our research demonstrates that the limitations of currently used technology likely allowed monkeypox cases to slip through the system. This problem was further exacerbated by the two-week delay that occurred during the diagnosis of the first monkeypox cases. If the 2003 outbreak had been smallpox instead of monkeypox, the situation could have been much worse because secondary spread of the virus to other victims would likely have occurred before the outbreak was recognized."
To conduct this research, Slifka and colleagues traveled to Wisconsin to test those who had been exposed to monkeypox in 2003. Although 72 potential cases were reported at that time, only about half of the cases have been officially confirmed. Directly following the outbreak, the CDC released a report that focused on 11 of the 72 cases. Of those 11, six cases were confirmed and the remaining five cases remained unconfirmed, until now.
The test the CDC uses to confirm monkeypox cases requires that the virus be directly identified in blood or tissue samples. Because monkeypox virus is eventually cleared by the body, the evidence is quickly wiped out, resulting in a high percentage of unconfirmed cases due to the limited window of opportunity for diagnosis. In comparison, OHSU's research team tested samples using a variety of methods. One such test, called the ELISA test, resulted in very accurate results (95 percent sensitivity, 90 percent specificity.) This high level of accuracy allowed Slifka and colleagues to correctly diagnose previously confirmed cases as well as confirm several probable,suspect cases of monkeypox that had remained unconfirmed for the last two years. Most importantly, Slifka's lab identified and confirmed three new cases of monkeypox that had previously gone undetected by the CDC.
The ELISA test is based on a Slifka lab research finding that specific genes found in the monkeypox virus are recognized by antibodies produced by the human immune system. By testing for this unique immune response, which remains detectable for years, researchers can accurately determine if the patient has been infected with the virus.