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Measles on rise in U.S., Europe: Are tourists to blame?

measles, boy, vaccine, stock, 4x3
measles, boy, vaccine, stock, 4x3
Measles cases are on the rise in Europe and are now showing up in the U.S.

(CBS) Measles is on the rise worldwide, and health officials in the U.S. and abroad are worried.

In Europe, 6,500 cases of measles have been reported so far this year, according to the World Health Organization. France is reporting the largest outbreak, with almost 5,000 cases seen from January to March alone. Outbreaks have also been reported in Germany, Belgium, Romania, Spain, Turkey, and the United Kingdom.

In the U.S., there have been reports of 98 measles cases in 23 states this year, including 13 in California, according to health officials. "We see that as worrisome," Dr. Gilberto Chavez, deputy director of the California Department of Public Health, told the Los Angeles Times.

Health officials think the outbreaks in the U.S. - where the disease had been thought to have been mostly eliminated - are being caused by unvaccinated Americans returning from abroad as well as from contact with unvaccinated foreigners who visit the U.S., health officials say.

Measles is a viral disease that causes high fever, coughing, and blotchy reddish-brown rashes. The virus lives in mucus and spreads to others by coughing and sneezing. The disease is so contagious that if one person has it, 90 percent of unvaccinated people close to that person will become infected. Children are most at risk for infection and hospitalization.

What will it take to stop the spread of measles?

"It is crucial that children and young adults are fully immunized with two doses of MMR (measles, mumps, and rubella vaccine)," Dr. Mary Ramsay, head of immunization at the UK's Health Protection Agency, told BBC News.