PORTLAND, Ore. -- Researchers at the Vaccine and Gene Therapy Institute(VGTI) at Oregon Health & Science University have developed newdiagnostic methods to better detect future monkeypox or smallpoxoutbreaks. The research also sheds new light on the 2003 monkeypoxoutbreak in the Midwest -- monkeypox is closely related to smallpox.This new information suggests that the 2003 outbreak was larger thanthe 72 cases reported by the Centers for Disease Control and Prevention(CDC). The research was released online this week by the medicaljournal Nature Medicine. The study will also appear in the September2005 print edition of the journal.
"The 2003 outbreak of monkeypox provided some incredibly valuableinformation about the country's level of preparedness for an infectiousdisease outbreak that is either naturally occurring or an act ofterrorism," said Mark Slifka, Ph.D., lead author and an assistantscientist at the VGTI, an assistant professor of molecular microbiologyand immunology in the OHSU School of Medicine and an assistantscientist at the Oregon National Primate Research Center. "Our researchdemonstrates that the limitations of currently used technology likelyallowed monkeypox cases to slip through the system. This problem wasfurther exacerbated by the two-week delay that occurred during thediagnosis of the first monkeypox cases. If the 2003 outbreak had beensmallpox instead of monkeypox, the situation could have been much worsebecause secondary spread of the virus to other victims would likelyhave occurred before the outbreak was recognized."
To conduct this research, Slifka and colleagues traveled toWisconsin to test those who had been exposed to monkeypox in 2003.Although 72 potential cases were reported at that time, only about halfof the cases have been officially confirmed. Directly following theoutbreak, the CDC released a report that focused on 11 of the 72 cases.Of those 11, six cases were confirmed and the remaining five casesremained unconfirmed, until now.
The test the CDC uses to confirm monkeypox cases requiresthat the virus be directly identified in blood or tissue samples.Because monkeypox virus is eventually cleared by the body, the evidenceis quickly wiped out, resulting in a high percentage of unconfirmedcases due to the limited window of opportunity for diagnosis. Incomparison, OHSU's research team tested samples using a variety ofmethods. One such test, called the ELISA test, resulted in veryaccurate results (95 percent sensitivity, 90 percent specificity.) Thishigh level of accuracy allowed Slifka and colleagues to correctlydiagnose previously confirmed cases as well as confirm severalprobable,suspect cases of monkeypox that had remained unconfirmed forthe last two years. Most importantly, Slifka's lab identified andconfirmed three new cases of monkeypox that had previously goneundetected by the CDC.
The ELISA test is based on a Slifka lab research finding that specificgenes found in the monkeypox virus are recognized by antibodiesproduced by the human immune system. By testing for this unique immuneresponse, which remains detectable for years, researchers canaccurately determine if the patient has been infected with the virus.
"While this research primarily focused on monkeypox, this sametechnology could also be used to better detect a smallpox outbreak,"said Slifka. "This is an active area of further investigation."
The test even works in cases where infection may not beobvious. For instance, three of eight subjects who had previoussmallpox vaccinations failed to show any outward signs of viralinfection and had no noticeable disease symptoms. The researchers foundthis particularly interesting because this virulent strain of monkeypoxvirus resulted in numerous hospitalizations. In one case that has beenpreviously reported, a child remained in a coma for 12 days.
Due to similarities between the monkeypox and smallpox viruses, thesmallpox vaccine likely kept these inoculated people from becomingseriously ill. The researchers believe these people were fullyprotected against monkeypox because smallpox vaccination can providecross-protective immunity against this virus.
"In our study, we found one subject who had fully protective immunitythat was maintained for 48 years after a single smallpox vaccination,"said Slifka. "In a previous study, we predicted that about 50 percentof previously vaccinated people would maintain fully protectiveimmunity against virulent poxvirus infections, and these findings aretotally in line with what we expected. What this means is that thereare more than 100 million people in the U.S. that have partial or evenfully protective immunity that is maintained after childhoodvaccinations -- an important point to consider if we were ever to bedeliberately attacked with smallpox or other dangerous poxviruses asweapons of bioterrorism".
The research was funded by OHSU, ONPRC and the National Institutes of Health.
Cite This Page: