Infectious Diseases : TB, Hantavirus

by Food and Drug Administration (FDA)

(Page 2 of 3)

If the body's immune system is impaired, the TB bacteria may begin to spread more widely in the lungs or to other tissues causing active TB infection.

The early symptoms of active TB include fatigue, weight loss, fever, chills, and night sweats. Once the infection has progressed, people may develop a cough or chest pain, or produce sputum that may contain blood. TB can spread beyond the lungs causing additional symptoms such as back pain or blood in the urine.

FDA recently approved a sputum test for TB that gives results in four to five hours, compared to the one to eight weeks required by conventional sputum culture tests. The Amplified Mycobacterium TB Direct Test is for use on specimens already shown likely to be positive for TB on an acid fast stain test. The new test allows treatment to begin sooner, but a follow-up conventional culture test must also be done.

TB is treated with a combination of several antibiotics, which have to be taken for six to nine months to be effective. CDC recommends that people with latent TB who develop HIV infection or another condition that suppresses the immune system receive preventive therapy with the antibiotic isoniazid, marketed under the brand name INH. People who have been in close contact with someone with active TB and test positive on a TB skin test should also take isoniazid, which is highly effective in preventing a latent TB infection from progressing to active disease.

Drug-resistant strains of TB develop when people stop taking their TB drugs too soon or take them incorrectly. About 90 percent of people with TB that responds to standard antibiotics are cured of the disease. But only 10 percent of those people afflicted with drug-resistant TB survive.

There has been a disconcerting increase in the number of drug-resistant TB cases in outbreaks scattered across the country. (See "The Rise of Antibiotic Resistant Infections" in the September 1995 issue of FDA Consumer.) Particularly disturbing are the 1 out of 10 cases of drug-resistant TB that have occurred in healthy people with normal immune systems. They died at the same rate as those with faulty immune systems afflicted with the drug-resistant TB.

Noting the ease with which TB is passed from person to person, a 1992 National Academy of Sciences report on emerging infections warned that drug-resistant TB "represents a major threat to health in the United States."

In response to the drug-resistance problem, FDA has pledged to speed up the review process for new TB drugs. One TB drug is currently being tested in a clinical trial, and another may soon undergo such testing.

A vaccine that can prevent TB from spreading beyond the lungs is available. But because the vaccine cannot reliably prevent TB lung infections in adults, it currently is not recommended for general use or for health-care workers, according to CDC. The vaccine is also problematic because it causes people to test positive for a TB skin test, which is the mainstay for TB surveillance in this country.

Hantavirus

The 1993 outbreak of hantavirus pulmonary syndrome (HPS) in the Southwest caught health officials by surprise. The new syndrome initially causes flu-like symptoms, and then causes its victims to gasp for air as their lungs fill with fluid. The disease kills about half the people it infects, usually within a week. There is no treatment approved specifically for hantavirus, but researchers are currently assessing the effectiveness of the antiviral drug Virazole (ribavirin) for HPS. A vaccine is being developed.

HPS is caused by a hantavirus named Muerto Canyon (Valley of Death) virus for the spot in New Mexico where it was isolated. It is carried by rodents and passed to people who inhale the aerosol particles emitted by the infected rodents' saliva, urine or feces. People can become infected with hantavirus after being bitten by rodents. Many people who have developed HPS live in mice-infested homes. One woman who developed the disorder, however, was exposed to rodents her pet cat dragged into her house. Another person succumbed to the disease after cleaning a rodent-infested barn. Hantaviruses are not passed directly from person to person.

Experts suspect that rodents in the western United States have harbored the Muerto Canyon virus for quite some time, but unusual weather conditions led to an explosion of the deer mouse population in the early months of 1993. The boosted mouse population apparently triggered the HPS epidemic by increasing contact between people and mice infected with the virus.

Since first described in the spring of 1993, more than 100 cases of HPS have been identified in 23 states, predominantly in the Western half of the country, according to CDC. The rodents that can carry the Muerto Canyon virus, however, live nearly everywhere in the United States.

The deer mouse population started declining shortly after the first HPS cases were reported. Between early 1994 and mid-1995, only 37 cases of HPS were reported to CDC, suggesting the hantavirus epidemic is waning.

People can stem their risk of a hantavirus infection by ensuring their homes and workplaces are free from rodents.

About the Author

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