June 2008
Feature Story

Reemerging pathogens, like emergent viruses, are a big problem, says William J. Bellini, PhD, chief of the CDC’s Measles, Mumps, Rubella, and Herpesvirus Laboratory Branch. “We do a certain amount of clinical virology here for measles, rubella, and mumps viruses,” Dr. Bellini says. “Those had been eliminated from the U.S. However, measles has made a slight comeback.” Reemergence of eradicated viruses requires what Dr. Bellini calls “a vigilant mindset—you can never let your guard down even for viruses that have been eliminated. It’s really a changing world.”

Measles outbreaks arise primarily among children of people who object to vaccination—personal belief exemptors—and are often imported from countries where vaccination is less prevalent. Dr. Bellini cites as the best example people coming from Israel who seeded a measles outbreak in New York City among certain Jewish groups who do not accept vaccination. Measles can also enter from Europe, where vaccination rates are lower, and this year and last year are what Dr. Bellini calls “banner years” for measles outbreaks in Europe. An outbreak in Arizona, primarily among people who were unvaccinated, originated from a person traveling from Switzerland. “That got going in a hospital environment where somehow there were unvaccinated persons,” Dr. Bellini explains. “It went on for about three chains of transmission and lasted about six weeks in the hospital environment.” China, too, has a lot of measles, which enters the United States with adoptees and their new parents.

Measles in Europe occurs, he explains, because “some physicians think that natural infection creates a better immune response and that the disease is not so bad. So in some countries health care providers have differing opinions regarding vaccination programs and are split 50/50 pro to con.”

Mumps also reemerged in the U.S. in 2006 with about 6,500 cases. The outbreak “came out of the blue,” began someplace in Iowa, and quickly involved nearly 20 states. Dr. Bellini believes that widespread vaccination changed the presentation of the disease as well as immune responses that laboratories had relied on to detect the virus. “We are now modifying and changing our tools to detect these viruses in vaccinated populations,” he says.

“Mumps is a different situation [from measles],” Dr. Bellini adds, “since it occurs mostly in vaccinated people. We don’t quite understand the reemergence of mumps, and the outbreak raises questions about vaccine efficacy.”

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