Chagas disease host prevalent in Southern Arizona

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PHOENIX (AP) -- A new study shows that more than 40 percent of "kissing bugs" collected by researchers in Tucson carry a parasite that can cause a disease that kills tens of thousands of people a year in Central and South America.

But while the number of bugs hosting the single-cell parasite that causes Chagas disease is much higher in the southern Arizona city than earlier thought, no human infections have been traced to bites that occurred in the state.

That may mean doctors are not looking for a disease that is rare in the U.S. But it is more likely that the triatomine insects don't act the same way as their cousins to the south, or that the disease is a different strain, said Carolina Reisenman, a University of Arizona research biologist. She co-authored the study, which is to be published in the March edition of the Centers for Disease Control and Prevention journal Emerging Infectious Diseases.

"People have been bitten here for a long time, for decades, so my suspicion is we should see cases already if the transmission is efficient," Reisenman said.

More research will be needed before an explanation is found.

Reisenman's team enlisted local residents to collect the bugs in and around their homes, and CDC researchers collaborated in the analysis, Reisenman said.

Of the 164 insects turned over to researchers, DNA tests showed more than 40 percent carried Chagas disease. The only previous research, in the early 1960s, showed 4 percent of the kissing bugs around Tucson carried the disease.

The results indicate that the risk of infection in southern Arizona may be higher than previously thought, the researchers concluded. The study doesn't measure infection risks in other parts of the southern U.S., where the bugs are known to live and also carry the parasite.

Chagas disease is endemic in poor areas in Latin American countries, where an estimated 8 million to 11 million people are infected, according to the CDC. In recent years, immigrants infected with Chagas have come to the U.S., and in 2009, the CDC estimated at least 300,000 migrants carried the disease.

It also is known to be carried by kissing bugs in the southern U.S., although the disease is rare here, with only seven cases of locally acquired infection identified.

Estimates on the number of worldwide deaths from Chagas per year range from 15,000 to 50,000. But the numbers are declining because of prevention and treatment efforts, said CDC researcher Ellen Dotson.

Kissing bugs transmit the disease as they drink blood from humans, typically at night, and spread the parasite through feces. After a brief period of relatively minor symptoms, including a sore at the bite and a fever, the disease usually goes dormant. It re-emerges years or decades later, with severe heart or gastrointestinal problems in about 20 percent to 40 percent of patients. There are treatments for acute infections, but once the disease causes major organ damage, it cannot be reversed.

The disease is also transmitted by blood transfusions, organ transplants and in childbirth. Screening of the blood supply began in most areas of the nation in early 2007, and the CDC says 1,000 infected donors have been identified. Nearly all donors acquired it in their home country, but a handful had never been in south or central America, and officials are investigating where they contracted the parasite.

The risk of infection is much greater for domestic animals like dogs, which are more often exposed to kissing bugs while outdoors, said Susan Montgomery, a CDC veterinary medical officer.

Reisenman said knowing that Tucson-area residents have a higher chance of exposure than previously thought will raise awareness of its potential in the health community.

"It's nothing to raise an alert, but as with a lot of these diseases, it's important to be ahead of the problem," she said.


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