Posted on 11/18/2003 7:03:04 AM PST by neverdem
A parasitic infection common in Latin America is threatening the United States blood supply, public health experts say. They are especially concerned because there will be no test for it in donated blood until next year at the earliest.
The infection, Chagas disease, is still rare in this country. Only nine cases are known to have been transmitted by transfusion or transplant in the United States and Canada in the last 20 years.
But hundreds of blood recipients may be silently infected, experts say, and there is no effective treatment for them. After a decade or more, 10 to 30 percent of them will die when their hearts or intestines, weakened by the disease, explode.
Chagas is still little known in the United States, but in Mexico, Central America and South America, 18 million people are infected, and 50,000 a year die of it.
Experts expect it to become better known as new tests are developed.
"I wouldn't say that it's as rare as hen's teeth, but it's rare," said Dr. Ravi V. Durvasula, a Chagas expert at the Yale School of Public Health. "It's one of the top threats to the blood supply, but it's an emerging threat."
Because the disease is most common in rural areas from southern Mexico to northern Chile, the threat is greatest in American cities with many immigrants from those areas.
Across the United States, said Dr. David A. Leiby, a Chagas expert at the American Red Cross, the risk of getting a transfusion of infected blood is only about 1 in 25,000.
But in 1998 in Miami it was found to be 1 in 9,000, he said, and in Los Angeles the same year, he measured it at 1 in 5,400, up from 1 in 9,850 only two years earlier.
No more recent study of the blood supply has been done.
The only routine screening for Chagas now is in the standard set of questions asked of donors — whether they come from or have visited a country where Chagas is endemic and whether they ever slept in a thatched hut.
But that often isn't reliable, said Dr. Louis V. Kirchhoff, a professor at the University of Iowa's medical school who researches Chagas in Guadalajara, Mexico, where the chance of getting infected blood is 1 in 126. Potential donors "are kind of leery of those questions," he said, and may not answer honestly.
Since 1989, several advisory panels to the United States Food and Drug Administration have recommended that all donated blood be screened for Chagas. But no test has been approved yet.
Last year, the F.D.A. invited diagnostics companies to create one, and the two largest, Abbott Laboratories and Ortho-Clinical Diagnostics, are trying. But representatives of the companies said they were under little deadline pressure. Abbott's test may be ready next year.
Little sense of urgency exists because "there are always new things that come up," Dr. Leiby said. Hepatitis and AIDS were followed by mad cow disease, West Nile virus and bacterial contamination of platelets, so "Chagas gets pushed to the side," he said.
Mary Richardson, a spokeswoman for Ortho, which hopes to have a test by 2005, added: "Clinical trials take time. There's only so much speeding up you can do."
Nonetheless, she added, "the F.D.A. feels it's the next biggest threat."
An F.D.A. spokeswoman said her agency did not like to rank all the threats to the blood supply — including hepatitis, AIDS and West Nile virus — but reiterated that "we would certainly recommend a Chagas test if one is developed."
Prevalence rates in Latin America vary widely, from 25 percent in Bolivia to 1 percent in Mexico.
It is not found on Caribbean islands like Puerto Rico, the Dominican Republic or Cuba.
In some countries, it is a serious threat to the blood supplies; in one Bolivian city, half of the blood was infected.
About 30 tests are used in different countries, but none meet F.D.A. accuracy standards. Some Latin American blood banks disinfect with gentian violet, but it is unpopular because it gives recipients a purplish tinge.
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The disease is named for Carlos Chagas, the Brazilian doctor who described it in 1909. It is caused by a protozoan, Trypanosoma cruzi, which infects humans in a particularly disgusting way. Reduviids, also called kissing or assassin bugs, drop down from the thatch, follow the trail of carbon dioxide to the mouths of sleeping humans and suck their blood. They leave behind a protozoan-laden drop of feces, which the sleeper often inadvertently rubs into the itching wound.
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Charles Darwin may have been infected on his travels; he suffered with Chagas symptoms for many years in England.
There is no vaccine and no effective treatment. The first phase, which starts within weeks of infection, may include fever and swollen glands, liver or spleen, but is rarely fatal except in infants and in adults with compromised immune systems. It is often misdiagnosed.
The disease can then lie dormant for 10 to 30 years, then kill suddenly as weakened organs rupture.
The failure of the blood industry and its regulators to develop a test since it was endorsed by a Blood Products Advisory Committee in 1989 seems to be a combination of bureaucratic inertia and divided responsibility for such a decision. Blood banks cannot use a test that the F.D.A. has not approved. The agency usually defers to its advisory committees, which have many experts from blood banks as members.
"It's a political process that is not always fully engaged," said Dr. Stuart J. Kahn of the Infectious Disease Research Institute, a Seattle group hunting cures for tropical diseases.
Dr. Hira Nakhasi, director of transfusion-transmitted diseases at the F.D.A., agreed that neither the blood banks nor his agency had been very aggressive. Things tended to move when "the public and media put pressure on," he said.
Cost concerns made blood banks hesitant, Dr. Kirchhoff said. It may cost $50 million to $100 million a year to screen the whole United States blood supply, he estimated, and "people will reasonably say, `Why should we do this if we're not seeing a lot of sick people?' "
Although perhaps 120 Americans a year get infected blood, he said, between 70 and 90 percent will not become seriously ill, and few of those who do will live long enough to die of Chagas.
Most transfusion recipients are fairly sick, and half die of other causes within two years anyway.
But he pointed out that the risk was growing rapidly. Census figures show that net immigration from Mexico is about 1,000 people a day, he said. Of those, 5 to 10 are probably infected.
Meanwhile, blood banks increased their appeals to Hispanics in the 1990's, under extra pressure when mad cow disease eliminated donors who had made long visits to Europe and AIDS eliminated gay men and other risk groups.
Interest in Chagas seems to be growing, Dr. Kahn said, because breakthroughs in biogenetics make it easier to attack diseases and because the interest of the Bill and Melinda Gates Foundation in third world health "put a lot of diseases up on the radar screen."
But seriously, many blood banks pay for blood. If you're a poor illegal looking for money, that would be one way to get it.
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