Massachusetts health authorities are on high alert for cases of the mumps, the painful viral illness that has reemerged in Maine and Maritime Canada in recent months, despite decades of vaccinations.
Before the outbreak, Maine had not reported a case in at least 20 years. Now mumps has spread across the state, reaching its southernmost county and making nearly 75 children and adults sick statewide since September.
Disease trackers suspect that the Maine outbreak was imported from Canada, where 1,140 people have fallen ill this year, 14 times the average for recent years. Most of the cases have been reported by three eastern provinces, Nova Scotia, New Brunswick, and Prince Edward Island.
Specialists in Massachusetts are watching the migration of mumps with increasing concern, knowing that many of the patients in Maine and Canada are college students, a group particularly susceptible because they are mobile and live in tight quarters, an ideal combination for disease transmission.
"We are exploring every possible mumps case," said Dr. Alfred DeMaria, director of communicable disease control for the Department of Public Health in Massachusetts, where only three cases have been reported this year.
"We're going to be especially vigilant after the holidays," he said, because Boston students may have contact with students from Maine schools during the break.
The resurgence of mumps illustrates the hardiness of a virus, the limitations of a vaccine, and the realities of a world so hooked on air travel that germs can spread from one country to another in a matter of hours.
Specialists said they believe that is exactly what happened with mumps. Like measles, it was a common childhood scourge that appeared headed for extinction in the United States. But in 2005, a strain widely circulating in the United Kingdom, where vaccination rates are significantly lower than in North America, was imported to a New York state summer camp.
Within a year, that same strain was identified as the culprit in a Midwest outbreak. And it is being blamed for the cases in Canada this year. "Mumps is essentially endemic in the rest of the world," said Dr. James Alexander, a medical epidemiologist at the US Centers for Disease Control and Prevention. "Canada and the United States were the two countries where mumps was close to being eliminated."
The virus is transmitted by direct contact with an infected person's saliva, meaning it can travel through a kiss or on utensils, towels, or tissues. It causes severe swelling of salivary glands and is heralded by fever, headache, body aches, and glandular tenderness where the jaw forms an angle. Rarely fatal, it can result in significant complications, including inflammation of the testes, brain swelling, meningitis, and sterility.
A vaccine introduced in 1967 led to a steep decline in mumps in the United States, but within two decades, the virus had reemerged.
"Mumps has undoubtedly been with us for millennia, and it's not likely to disappear just because we develop an effective vaccine," said Dr. Kenneth McIntosh, a disease specialist at Children's Hospital Boston.
One pivotal lesson derived from the return of the mumps in the late 1980s: A single dose of vaccine did not provide enough of a shield. It was then that disease specialists began recommending that children receive two doses and that schools bar students who were not vaccinated.
As Canadian specialists began investigating this year's outbreak, they quickly homed in on the vaccination history of patients, unearthing important clues. Nearly 73 percent had received only a single dose of vaccine, while 19 percent had no vaccination at all. Those who received at least one dose generally had milder cases.
"I like to compare this disease to a heat-seeking missile," said Jeannette Macey, an epidemiologist with the Public Health Agency of Canada. "If there are people in the population who are not protected, it's going to find them."
In Maine, authorities are collecting comparable data, but they know already that many of the adults who became infected probably only got a single dose earlier in life. At the University of Southern Maine, where many of the students are older, at least 10 people have fallen ill, a spokeswoman said.
Disease specialists from Maine and the federal CDC are also continuing to investigate exactly where the virus came from, running sophisticated genetic testing and conducting extensive interviews. "It's not surprising that Maine would have cases," said Dr. Dora Mills, director of Maine's CDC. "New Brunswick is adjacent to Maine, and Nova Scotia might as well be, because there are several boats that go back and forth every day."
Stephen Smith can be reached at firstname.lastname@example.org.