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In the late 1960s, after seeing such deadly diseases as smallpox, polio, and rheumatic fever get tamed by vaccines or antibiotics, Surgeon General William H. Stewart declared that it was time to close the book on infectious diseases and pay more attention to chronic ailments such as cancer and heart disease.
This commonly held belief that the war on infectious diseases could be won has been shattered by a score of new or reemerging diseases that have surfaced in epidemics scattered across the globe over the last 15 years, with some occurring within just the last year or two.
The new epidemics, combined with a deeper understanding of disease dynamics and the tricks microbes have up their sleeves, have shaken the medical community and led to a less rosy outlook. An article in the Jan. 17, 1996, issue of the Journal of the American Medical Association reported that infectious disease is now the third leading cause of death, after heart disease and cancer. Deaths from infectious disease rose 58 percent between 1980 and 1992, according to the article by Robert W. Pinner, M.D., of the national Centers for Disease Control and Prevention, and colleagues. Most of the increase is from AIDS cases. Yet even without AIDS cases, the death rate from infectious diseases rose 22 percent.
Some infectious disease experts wager future epidemics will take a greater toll on human life than those in the past, despite medical advances made over the past century. We are increasingly more vulnerable to infectious diseases, these experts point out, because of the growing proportion of people residing in urban areas, which act as magnets for epidemics. In 1800, less than 2 percent of the world's population lived in urban communities. By the year 2000, however, that fraction is expected to rise to 50 percent, according to the National Academy of Sciences.
Air travel, in addition, allows diseases to spread between cities on opposite ends of the globe in a matter of hours.
Prominent on the list of new or reemerging diseases that have health officials concerned are invasive strep infections, tuberculosis (TB), hantavirus pulmonary syndrome, malaria, and dengue. The Food and Drug Administration is responsible for insuring the safety and effectiveness of the drugs and vaccines used to curb infectious diseases.
The map below (a 95K JPEG graphic) shows some of the locations of new or reemerging infectious diseases and the year the first recent cases appeared. (Source: Centers for Disease Control and Prevention.)
![[map showing recent appearances of infectious diseases]](../graphics/1996graphics/diseases.jpeg)
Deadly Strep
Changes in the Streptococcus bacterium that give it more punch are credited with causing recent outbreaks of "flesh-eating" strep and streptococcal toxic shock syndrome (strep TSS). The latter disorder killed puppeteer Jim Henson in 1990.
Both these infections are caused by invasive strep--a type of Streptococcus that more readily spreads in the body than the types that cause strep throat. Studies by Dennis Stevens at the Veterans Affairs Medical Center in Boise, Idaho, suggest invasive strep is armed with two powerful toxins. In the body's furious attempt to rid itself of one of the toxins, the immune system can foster the destruction of infected muscle tissue or the sheath that covers the muscle (the flesh-eating manifestation) or prompt the body to go into shock, which is often fatal, or both. Damage also is wreaked by the other toxin, an enzyme that destroys tissue by breaking down protein.
Invasive strep usually enters the body through minor injuries, such as deep bruises, punctures, or chicken pox blisters. Only rarely is the deadly form of strep acquired through person-to-person contact. People with invasive strep usually don't complain of a sore throat, but rather often have flu-like achiness and fatigue that is followed by a number of symptoms, including pain in one region of the body, cough and difficulty breathing, or painful skin that is red, hot and swollen and gradually purples and forms blisters. This can be accompanied or followed by confusion, low blood pressure, and coma.
The antibiotics penicillin, erythromycin and clindamycin are the drugs of choice for treating invasive strep infections; the earlier treatment is begun, the better the outcome. Surgical removal of infected tissue, possibly including limb amputation, may be necessary. Researchers are currently testing a vaccine for invasive strep.
CDC estimates that about 15,000 cases of invasive strep infections occur each year in the United States, and studies by Stevens and others suggest one out of three people with invasive strep die. The infection can kill in less than a week.
Like most diseases, invasive strep is not new; China experienced an epidemic of flesh-eating strep in 1924, and strep infections were a major cause of death in Chicago and other cities in this country in the middle of the 19th century. It's not known for certain whether invasive strep currently is on the rise in this country. At this point, however, it is still considered a rare disease.
Tuberculosis
After a comforting steady decline since the 1950s, TB incidence in the United States began to climb in 1985, setting off alarms in the medical community. According to CDC, in 1994 there were 24,361 cases of TB in the United States--about 2,000 more cases than in 1984.
TB's comeback in this country is tied to the rising numbers of people whose immune systems are weakened by HIV infection, cancer and chemotherapy, or the drugs taken following an organ transplant. A resurgence of the disease is also being fostered by increasing poverty and drug abuse, as well as by increasing numbers of immigrants to this country with TB.
Well-known to the ancient Egyptians, TB is caused by airborne bacteria expelled from the lungs when a person with active TB coughs, sneezes or speaks. Repeated exposure to these droplets can infect another person's lungs.
The immune defenses of healthy people usually prevent TB infection from spreading beyond a small area of the lungs by creating a barricade around the bacteria. This walled-up infection is called latent TB and may be present throughout a person's life. People with latent TB test positive on the TB skin test. About 10 to 15 million people in this country have latent TB.
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.
Airport Malaria
International jet-setting has fostered recent outbreaks of malaria in the United States. Malaria is such a common import to countries that the term "airport malaria" was coined to describe the outbreaks of the disease that have occurred among travelers. About 1,000 cases of malaria are imported into this country each year, according to CDC.
Malaria causes flu-like symptoms, and in severe cases can cause coma, severe anemia, kidney failure, difficulty breathing, or death. The disease is passed from person to person by mosquitoes that harbor the malaria-causing parasites.
Malaria was a major problem in this country during George Washington's time and, until the 1930s, was a major killer in the southern states. The disease was virtually eradicated from the United States by 1955, following a major campaign in which mosquito-infested areas were sprayed with the pesticide DDT and swamps were drained or filled with oil that killed mosquito larvae. People were also encouraged to screen the windows of their homes.
Similar efforts worldwide shrank malaria's territory, but only temporarily as mosquito-control efforts abated, mainly due to a lack of funds, and mosquitoes resistant to the effects of pesticides increased. According to the National Institute of Allergy and Infectious Diseases, each year malaria now infects 300 million to 500 million people globally and kills as many as 3 million.
There's concern that malaria might once again take root in the United States because most states harbor mosquitoes that can carry malaria parasites. Particularly disturbing are the recent small outbreaks of malaria in California, Florida, Texas, New Jersey, and New York City. Most of these cases were probably spread by infected immigrants or migrant workers via local mosquitoes, according to CDC.
"The reintroduction of significant malaria into this country is ... very possible," said Philip Coyne, M.D., medical officer in FDA's division of anti-infective drug products.
Malaria can often be effectively treated with quinine or related compounds. Drug-resistant strains of malaria parasites are posing a problem worldwide, however, and raising the need for new antimalarial drugs. FDA approved Halfan (halofantrine) in 1992. Its developer, SmithKline Beecham, Inc., has chosen not to market it in the United States. Some strains of malaria are already resistant to it. Other antimalarial drugs and vaccines are currently being tested.
Break-Heart Fever
Another mosquito-spread illness on the rise worldwide and likely to make a comeback in this country is dengue, which an 18th century Philadelphia doctor called "break-heart fever" because of the depression that often ensues following the illness. Dengue, which is caused by a virus, is characterized by a sudden onset of high fever accompanied by severe headache and muscle, joint and eye pain. A red rash can also develop all over the body. The rash may be accompanied by itching and scaling.
A severe form of dengue, known as dengue hemorrhagic fever, causes bleeding from the mouth, nose and vagina. Gastrointestinal bleeding and numerous bruises also often occur. Such bleeding can trigger a loss of blood pressure that can cause the body to go into shock. As many as 1 out of every 10 people who develop dengue hemorrhagic fever dies. There is no treatment for dengue and dengue hemorrhagic fever, although vaccines for the disorders are currently being developed.
Over the last 15 years, as mosquito control programs abated, dengue has spread like wildfire. In the 1980s, major outbreaks spread throughout Latin America, including Mexico, and the incidence of dengue hemorrhagic fever skyrocketed.
The United States hasn't had any major epidemics of dengue since the 1940s. But there are travelers to this country who come down with the disease each year, and a small number of people have developed dengue from local mosquitoes in Texas. Both species of mosquitoes that carry the dengue virus are firmly established in several southeastern states.
People traveling to dengue- and malaria-infested areas should use DEET-containing insect repellent and stay in lodgings with screened windows and mosquito nets for sleeping. Preventive drug therapy for malaria is also advised. Travelers should consult with their physicians about such treatment before leaving the country.
Other Health Threats
Other possible resurgent and emerging diseases include a dangerous kind of E. coli infection spread by contaminated meat, drug-resistant cholera, deadly Ebola infection, and a new disease called human granulocytic ehrlichiosis, which is spread by the type of ticks that can also carry Lyme disease.
Experts can't predict if any of these diseases will become a great problem. The best protection is to be aware of the possibility and take precautions to prevent their spread. As a 1992 National Academy of Sciences report on emerging infections points out, "despite a great deal of progress in detecting, preventing, and treating infectious diseases, we are a long way from eliminating the human health threats posed by ... a broad array of microbes."
Margie Patlak is a writer in Elkins Park, Pa.