A rare form of tuberculosis caused by illegal, unpasteurized dairy products, including the popular queso fresco cheese, is rising among Hispanic immigrants in Southern California and raising fears about a resurgence of a strain all but eradicated in the U.S.
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Cases of the Mycobacterium bovis strain of TB have increased in San Diego county, particularly among children who drink or eat dairy foods made from the milk of infected cattle, a study in the journal Emerging Infectious Diseases shows.
But the germ can infect anyone who eats contaminated fresh cheeses sold by street vendors, smuggled across the Mexican border or produced by families who try to make a living selling so-called “bathtub cheese” made in home tubs and backyard troughs.
Scientists at the University of California San Diego School of Medicine are warning that improved screening, treatment and public education are necessary to prevent the spread of the disease that now accounts for about 10 percent of all new cases of TB in that border region — and, perhaps, others.
“M. bovis TB is a disease of antiquity,” said Timothy Rodwell, a researcher who led the study published by the federal Centers for Disease Control and Prevention. “It is important that it not be allowed to re-emerge as a cause of TB in this country.”
Unlike typical TB, caused by the M. tuberculosis strain, the bovine variety isn’t easily spread through human-to-human contact. It settles less often in the lungs, making it less likely to be transmitted through breathing and coughing, Rodwell said.
Rare strain resists drug treatment
However, the M. bovis bug is resistant to front-line drug therapy and adults who contract it are more than twice as likely as those with traditional TB to die before treatment is complete.
Researchers studied nearly 3,300 culture-confirmed cases of TB in San Diego county between 1994 and 2005, the study showed. Some 265 of the cases were identified as the bovine TB. Though the number of cases remained small, they increased by nearly 65 percent over time, rising from 17 cases a year to 28 cases a year.
By 2005, more than half the M. bovis cases were diagnosed in children younger than 15, the study said. Nearly all of the cases were in Hispanics, and 60 percent were in people from Mexico. Between 2001 and 2005, 19 adults with M. Bovis died before or during treatment.
That worries TB health experts, who say that the small numbers belie a potentially large problem.
“I wouldn’t want to characterize it as increasing in epidemic proportions,” said Dr. Kathleen Moser, director of tuberculosis control programs for San Diego County.
“But it’s clearly being seen, and being seen in places where people drink unpasteurized milk and eat unpasteurized dairy products.”
Demand for Hispanic cheeses has skyrocketed in California, where 108 million pounds of legal, properly pasteurized queso fresco and other cheeses were produced last year, according to the California Department of Food and Agriculture.
Last year, Moser was concerned enough about dangerous, illegal varieties to launch a public health campaign that included ads on Spanish-language television stations and new brochures that warned families to beware of infected cheese.
Officials seize illegal cheese
Agriculture officials have been cracking down on illegally produced cheese, including more than 375 pounds of so-called “bathtub cheese” seized from an open-air market in San Bernardino last year, according to Steve Lyle, the agency’s director of public affairs. Such cheeses have been found to be colonized with salmonella, listeria, E. coli and M. Bovis TB.
The problem stems from cattle in Mexico, where M. Bovis infects an estimated 17 percent of herds. In the U.S., the problem is limited to occasional outbreaks among isolated herds. Overall, the U.S. virtually eradicated the M. Bovis variety in the 1900s, Rodwell said.
TB officials in the U.S. want to watch the trend closely. Although there are about 9 million new cases of TB in the world each year and about 2 million deaths, cases in the U.S. have dropped dramatically. More than half of the 13,300 U.S. cases a year are now concentrated in people born outside the U.S.
Rodwell cautioned that people worried about the M. Bovis strain of TB should pay closer attention to dairy products, not people.
“It is NOT a disease you are very likely to get from a foreign-born person,” he said in an e-mail. “The increase in M. bovis cases is more about what you eat, not where you were born.”
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