In science fiction movies and tabloid magazines, new diseases "suddenly drop in from outer space or come up from the depths of the ocean," notes Stephen Ostroff, associate director of epidemiology for the National Centers for Infectious Disease, part of the Centers for Disease Control and Prevention (CDC). In the real world, Ostroff says, truly new diseases are rare, if they exist at all. Most newly identified diseases--from deadly Ebola in Africa to the hantavirus that swept through the southwestern United States in 1993--are relatives of preexisting bacteria or viruses. Almost always, these disease-causing agents emerge within a new host population or geographic region because of environmental changes resulting from human activities.
Urbanization, for example, may have played a role in the emergence of human immunodeficiency virus (HIV), says Stephen Morse, an assistant professor of virology at The Rockefeller University. Though the precise origin of HIV remains uncertain, Morse says, a rural resident of Liberia may have eaten a monkey afflicted with a simian version of the disease. HIV emerged only after the man moved to the city, where he infected others. "With rare exceptions, most of the disease emergence or reemergence that we've seen in recent years has had a human fingerprint on it," says Ostroff .
Diseases can flourish and spread to new geographic regions because of global warming, land-use changes, technological changes, drug resistance, pesticide resistance among disease-bearing insects, and contamination of air, soil, or water. Since high-speed, long-range transportation now makes it possible to circle the globe in days, diseases can easily hitchhike from region to region.
When it comes to preventing emerging diseases, the stakes are high in both human and economic terms. Costs associated with treating sexually transmitted diseases (excluding Acquired Immune Deficiency Syndrome or AIDS) may reach $5 billion annually, according to a 1994 CDC report, Addressing Emerging Infectious Disease Threats. Intestinal infections generate another $30 billion in direct costs and lost productivity every year, the report says, and hospital-acquired infections racked up $4.5 billion worth of bills in 1992 alone. "Infectious diseases remain the leading cause of death worldwide," the report adds, and an increasing number of cases are linked to environmental changes.
Global Climate Change
Of the environmental changes linked to disease, the risks associated with global warming are particularly troubling, says Paul R. Epstein, a faculty member at the Harvard School of Public Health. Warming estimates vary, but according to climatologist Thomas R. Karl, a senior scientist at the National Oceanic and Atmospheric Administration's (NOAA) National Climatic Data Center, surface temperatures increased between 0.3°C and 0.6°C (0.5°F and 1.1°F) during the last century. Warming has been strongest at night in the mid-to-high latitudes of the Northern Hemisphere, says Karl.
Epstein fears that continued global warming could cause widespread outbreaks of malaria and other mosquito-borne diseases. A mosquito's range, reproduction, and biting rates can be enhanced by warmer weather, Epstein reports in a 17 January 1996 article in the Journal of the American Medical Association. At the same time, he says, warmer waters would support increased growth of fish-killing algae, and refugees from flooded coastal regions might overwhelm city water and sanitation systems.
Malaria--a potentially fatal mosquito-borne ailment resulting in fever, headaches, nausea, vomiting, diarrhea, and fatigue--now claims an estimated 2 million lives annually. If global warming continues, the disease could kill another 1 million people every year as parasite-bearing mosquitoes spread to new geographic regions, says Rita R. Colwell, a microbiology professor and president of the University of Maryland's Biotechnology Institute. Already, "malaria is making a comeback," Colwell warned when she lectured at the 1996 American Association for the Advancement of Science meeting as outgoing president of the organization.
A doubling of atmospheric carbon dioxide levels over the next 100 years could boost temperatures by 1.5°C to 4.5°C (about 3°F to 9°F), Karl says. Sea level is expected to rise by 15-90 cm during the same period, according to Human Health and Global Climate Change, a 1996 report by the National Science and Technology Council and the Institute of Medicine of the National Academy of Sciences.
Such dramatic environmental changes would be devastating to human health, Epstein says. If surface temperatures jump by 2°C over the next century, he adds, malaria, dengue, yellow fever, encephalitis, and cholera will run rampant.
Shellfish poisoning--and resulting neurological illness in humans who eat the seafood--can occur with alarming frequency when waters are warm enough to support increased toxic algal blooms, notes JoAnn M. Burkholder, an associate professor of aquatic ecology at North Carolina State University. Burkholder's recent studies have focused on a dinoflagellate named Pfiesteria piscicida, which is known as an "ambush-predator" because it targets certain fish. Attracted by fish secretions, the Pfiesteria piscicida puts fish into a narcotic stupor, strips off and eats their skin, then suffocates its victims by paralyzing them. These newly identified dinoflagellates are so toxic, in fact, that they've been known to cause skin lesions and short-term memory loss in fishermen and laboratory workers.
Pfiesteria piscicida may flourish when waters are loaded with nutrients such as nitrogen and phosphorus from farm runoff, industrial waste streams, or natural sources. And the dinoflagellates proliferate most readily when water temperatures range from 79°F to 91°F. "Increased warming trends would tend to encourage their growth," Burkholder says. Likewise, waters between 69°F and 82°F are ideally suited for the growth of the cholera Vibrio, says Martin Hugh-Jones, a professor at Louisiana State University's School of Veterinary Medicine.
Of course, if it gets too hot in certain areas, Morse points out, disease-bearing pests might simply perish there. In that event, "we may see malaria and dengue in New York City and Chicago again," he says. "But we may lose it in all other places where we currently worry about it."
Global warming will cause rising sea levels and flooding, which will undoubtedly result in crop losses. Food distribution systems could also be disrupted by civil war as feuding factions are forced to share increasingly limited resources. Research by Melinda A. Beck, an assistant professor at the Frank Porter Graham Child-Development Center at the University of North Carolina-Chapel Hill, suggests that nutritional deficiencies might actually prompt viruses to mutate and become more virulent among malnourished populations. Prompted by the observation that people in parts of China who are deficient in selenium are particularly susceptible to cardiac infections, Beck fed mice a diet deficient in either selenium or vitamin E, then injected them with coxsackie B, an RNA virus known to be harmless. Unlike a control group of well-fed mice, the malnourished rodents quickly showed signs of heart disease, says Beck. By comparing the genetic structure of benign coxsackie B with virus samples extracted from the sick mice, Beck determined that "what came out . . . is not what went into them." Though it's not yet clear exactly how dietary deficiencies could cause viral mutations, Beck speculates that a malnourished immune system may help RNA viruses replicate faster, thereby increasing the risk of genetic errors that cause mutations. Her study of selenium-deficient mice, published in the May 1995 issue of Nature Medicine, may offer the first clear evidence of a link between dietary deficiencies and disease evolution.
Between 1979 and 1996, atmospheric ozone over the Northern Hemisphere was depleted by 10-25%, NOAA announced on 24 April 1996. Some repletion should begin by the year 2000, thanks in part to an international ban on the production of ozone-destroying chlorofluorocarbons. But continued depletion of the earth's gaseous shield could make people more susceptible to disease, Epstein says, because increased exposure to ultraviolet radiation suppresses immune system responses.
Even if global warming doesn't pose the suspected threat, Colwell says, communities around the world are already experiencing public health problems associated with El Niño, a periodic warming of waters in the tropical Pacific that causes wild fluctuations in precipitation, resulting in flooding and droughts. By understanding the link between climate change and disease, Epstein says, communities could respond more effectively to toxic algal blooms triggered by warming as well as other weather-related diseases such as a recent malaria outbreak in Sri Lanka, where drought-starved rivers turned into shallow pools perfect for breeding mosquitoes. Someday, he adds, improved disease monitoring and weather surveillance systems may prevent a recurrence of pneumonic plague, which struck India three years ago when temperatures soared to 124šF, killing livestock and generating clouds of fleas.
The 1993 emergence of hantavirus pulmonary syndrome (HPS) in the southwestern United States may be another example of El Niño's effects on public health. More than 130 people suffered sudden cardiac arrest after breathing air contaminated by feces from infected rodents, reports Robert R. Parmenter, a biologist at the University of New Mexico in Albuquerque. Roughly half the victims died. Though Parmenter's data are still preliminary, he says El Niño may have prompted an explosion of the rodent population, because unusually abundant spring rains boosted the growth of the vegetation that feeds the animals.
Source: Addressing Emerging Infectious Disease Threats: A Prevention Strategy for the United States, Department of Health and Human Services, Centers for Disease Control and Prevention, (1994).
Urban Breeding Grounds
Cities have provided breeding grounds for disease ever since 5 b.c., when Rome was home to 1 million residents, writes author Laurie Garrett in The Coming Plague. Back then, she reports, only one in every three city dwellers lived to be 30, compared with 70% of rural residents. Whenever rural populations migrate to cities, Morse notes, they carry a diverse array of microbial luggage. In fact, many zoonotic diseases--those originating in animals--"may well go unnoticed so long as the recipients remain isolated," Morse wrote in the January-March 1995 issue of Emerging Infectious Diseases. "But with increasing movement from rural areas to cities, such isolation is increasingly rare."
Worldwide, the population in 425 cities will reach 1 million or more by the year 2000, according to a 1992 report by the Institute of Medicine (IOM) entitled Emerging Infections: Microbial Threats to Health in the United States. Global warming could exacerbate urban overcrowding, Epstein says, because coastal residents would flock to inland cities as ice caps melt and flood shore communities. With or without global warming, demographers say, Mexico City's population is expected to reach 30 million people in the near future. As the populations in cities such as Seoul and Calcutta approach 20 million people in the next century, overcrowding could promote outbreaks of cholera, which is frequently transported by water systems. "In many parts of the world," the IOM report notes, "urban population growth has been accompanied by overcrowding, poor hygiene, inadequate sanitation (including wastewater disposal), and insufficient supplies of clean water." Already, Cairo city officials cannot provide enough clean water for the city's 188 million residents. (see EHP, March 1996, p.263)
Today's urban residents are more susceptible to diseases carried by mosquitoes and rodents, particularly in developing countries. The global incidence of dengue--a mosquito-borne illness signaled by a sudden fever, headaches, achy joints and muscles, nausea, hemorrhagic bleeding, and even vascular collapse--has skyrocketed since 1956, with an average of 29,803 hemorrhagic-type cases reported each year. Though the disease is rare in the United States, the hemorrhagic strain is a leading cause of death among children in Southeast Asia. Often, the report says, "increased urbanization, densely populated areas, and poor sanitation play a significant role" in the spread of dengue.
The prevalence of water containers and discarded junk can boost mosquito populations in cities. In the United States alone, a quarter-billion tires are discarded every year, and several million more are imported for retreading. Mosquitoes responsible for dengue, yellow fever (endemic to Africa and South and Central America), and viral encephalitis "prefer to lay their eggs in water that collects in [such] containers," the IOM report notes.
Land-Use Changes
Although Lyme disease was virtually unknown in the United States before the 1960s, nearly 70,000 cases of the disease were reported between 1982 and 1994, according to David T. Dennis, chief of the CDC's Bacterial Zoonoses Branch. Affecting the skin, nervous system, heart, and joints, Lyme disease is transmitted to humans by deer ticks infected with the Lyme spirochete, a microbe that incubates inside mice before latching onto deer. Symptoms include a red "bull's-eye" lesion around the tick bite, followed by fatigue, headaches, stiff joints, and sometimes neurologic and cardiac abnormalities. Lyme disease is the direct result of cleared land, "which then returned to deciduous forest, providing the right circumstances for deer invasion," Dennis says. In the 1800s, the IOM report explains, the eastern United States was left virtually treeless after most land was cleared for farming and firewood. As farmers moved west, abandoned fields were retaken by forest. Because large predators had fled most areas, however, the deer population exploded. The proliferation of housing developments near wooded areas has exposed countless suburbanites to infected ticks.
Dam construction and new farming practices can also promote disease emergence. In 1977, for example, construction of Egypt's Aswan Dam precipitated an outbreak of Rift Valley fever, which causes hemorrhagic fever and hepatitis. Almost 600 people died, and 200,000 others fell seriously ill. The dam stabilized the Nile River, but it also established ideal breeding pools for mosquitoes. In Argentina, the conversion of grassland for growing maize prompted the proliferation of a rodent known to carry the Junin virus, similar to hantaviruses. An increased number of Junin virus cases were reported during the harvest season. A change from single-species farming to pig and duck farming in China may allow pigs to serve as "mixing vessels" for new types of influenza originating in ducks, Morse says.
Air, Water, and Soil Contamination
In the spring of 1993, an estimated 403,000 people in the Milwaukee, Wisconsin, area suffered acute watery diarrhea, painful abdominal cramping, nausea, vomiting, and fever. For most victims, the agony dragged on about nine days. The cause, researcher William R. Mac Kenzie says, was Cryptosporidium (commonly referred to as "crypto"), a gastrointestinal parasite that spreads from animal or human feces to fingers, food, and water.
Mac Kenzie, a CDC epidemiologist, was quickly summoned to Milwaukee that spring. His study of the outbreak included a search for crypto oocysts in treated water, a telephone survey of Milwaukee residents, and stool-sample analyses. Key to the investigation was Mac Kenzie's examination of crypto-contaminated ice frozen between 25 March 1993 and 9 April 1993.
Even now, he says, the exact source of Milwaukee's crypto outbreak remains a mystery. "It could have been from agricultural runoff, or it could have been from human sewage," he says. "It may have to do with currents within Lake Michigan and water temperature or wind velocity. This is all speculative."
Whatever the source, the parasites clearly made their way into Milwaukee's drinking water; Mac Kenzie discovered high crypto levels in treatment plant samples. Because it's resistant to chlorine, crypto isn't easily scrubbed from drinking water supplies. The pores in standard water-treatment filters are about 70 times too large to capture the micron-sized parasites, he notes.
Water-treatment regulations haven't changed since the 1993 epidemic in Milwaukee, Mac Kenzie says. But the CDC has teamed up with the EPA to study the problem. Meanwhile, outbreaks continue. In 1994, crypto struck again in Las Vegas, Nevada.
Around the world, large ships draw water for ballast and later release it, sometimes contaminating drinking water. According to a 2 July 1993 article in Science, ballast contamination of water is a serious and widespread problem. Authors James T. Carlton and Jonathan B. Geller mapped the journey of plankton samples from 25 Japanese ports to ballast water released by 159 cargo ships in Coos Bay, Oregon. "The ecological roles and impacts of invading species can only be partially predicted from knowledge of their biology and ecology in donor regions," they warned.
Ballast water may transport bacteria and viruses, along with algae, from port to port, Colwell says. In the 1970s, Colwell made a startling discovery: the cholera Vibrio can remain dormant inside algae, biding its time until warm water temperatures spur it back into action. A Chinese freighter may have triggered a massive cholera epidemic in 1991 by releasing contaminated water near Lima, Peru. Because drinking water wasn't chlorinated, the disease ultimately killed 3,538 people and made 336,554 others sick throughout the Western Hemisphere, Garrett reports.
E. coli is perhaps most notorious in the United States for its role in killing four children and causing severe bloody diarrhea in 500 other Washington State victims who ate contaminated hamburgers in 1993. But E. coli can also cause illness when it contaminates the environment. A 1991 outbreak resulted from people swimming in a lake fouled by the bacterial pathogen, according to the CDC's report, Addressing Emerging Infectious Disease Threats. Outbreaks of E. coli are a growing public health problem worldwide because of increasing resistance to antibiotics among these bacteria, Garrett says.
From Animals to Humans
Zoonotic diseases are "an important and potentially rich source of emerging diseases," says Morse. These diseases can be transferred to human populations through urbanization, ecological changes, or research activities. For example, a group of nonhuman primates from Uganda, slated for use in vaccine research, caused a deadly viral illness among humans in Marburg, Germany, in the late 1960s, according to the 1992 IOM report. A similar Filoviridae virus, Ebola, killed hundreds in Africa in the mid-1990s. In 1989, when a Filoviridae virus was discovered among nonhuman primates shipped from the Philippines to a U.S. research facility in Reston, Virginia, scientists feared the worst. However, although the virus infected some humans, no one got sick. In April of this year, 50 monkeys were euthanized at a research facility in Alice, Texas, after scientists discovered that the animals carried the same Reston virus.
The origin of HIV is unclear, but nonhuman primates displaced by land-use changes may have played a part in the emergence of the disease among humans. Shrinking primate habitats and other factors "opened the possibility of cross-species transmission among three or more monkey/chimp species," Garrett says.
Creutzfeldt-Jakob disease (CJD) is a devastating illness that causes severe brain damage, but it usually only strikes the elderly. When a number of British children were stricken by CJD recently, the cases triggered panic among the beef-eating public. "Mad cow disease," or bovine spongiform encephalopathy (BSE), was fingered by some as the likely cause of CJD in children.
Scientists haven't shown how BSE from cows might mutate to cause CJD in humans, and some say such species-to-species transmission is highly unlikely. "BSE appears to be a purely bovine disease," says Hugh-Jones. "There's no obvious connection [to CJD] at all."
Nevertheless, a handful of researchers wonder whether abnormal protein folding might allow BSE to circumvent the so-called species barrier. Infectious particles called prions are proteins that may be capable of reproducing without genetic code material, the researchers say. When prions from hamsters are exposed to abnormal proteins from other species, cross-species mutations occur spontaneously, according to research by a team directed by Richard A. Bessen of the National Institute of Allergy and Infectious Diseases, published in the 22 June 1995 issue of Nature. Despite this intriguing finding, however, the link between BSE and CJD remains speculative.
The Antibiotic Paradox
Professor Stuart B. Levy of the Tufts School of Medicine points out that antibiotics are so widely used among human and animal populations that they've become pervasive throughout the environment. Many diseases, including some forms of tuberculosis and malaria, are now impervious to antibiotics. In fact, "more than 90% of strains of Staphylococcus aureus (one of the most common disease-producing organisms in humans) are resistant to penicillin and other beta-lactam antibiotics," according to the 1995 Report of the American Society for Microbiology Task Force on Antibiotic Resistance.
According to the CDC, tuberculosis kills more people around the world than any other infectious disease. Until 1985, tuberculosis had been in decline for more than three decades, particularly in the United States. Currently, 8 million new cases are diagnosed each year worldwide, with 2.9 million fatalities each year. Although increased antibiotic resistance may be one factor in the resurgence, increased poverty, homelessness, substance abuse, and lack of access to health care are also cited by the CDC as causes.
Enterococci, the most common bacterial source of hospital-acquired infections, are rapidly learning to resist antibiotic treatment. Between January 1989 and March 1993, the American Society for Microbiology report says, U.S. hospitals reported a 20-fold increase in Enterococci resistant to the antibiotic vancomycin. The report notes that "vancomycin is often the last weapon available against these deadly microbes."
Some observers now fear that resistant Enterococci could share their resistance genes with staph and strep bacteria. "Such a bacterial strain, if it did emerge, would be virtually incurable and extremely dangerous," Garrett explains, "for it would possess not only special drug-resistant genes but also those for heightened virulence."
Pneumococci, a source of potentially fatal pneumonia, meningitis, bloodstream infections in the elderly, and middle-ear infections in children, are also gaining antibiotic resistance. The same holds true for certain strains of tuberculosis and malaria. At one time, chloroquine was the most commonly prescribed antimalarial drug. "Today," the 1992 IOM report says, "there are only a few areas in the world where chloroquine is effective." Chloroquine's successor, mefloquine, is also rapidly losing its efficacy.
Bacteria are built to survive and adapt to change, according to Levy, also author of the book The Antibiotic Paradox. Any bacteria that survive antibiotic treatment are more likely to flourish. Resistance can also be transferred from bacteria to bacteria via plasmids (genetic material), thanks to a "bacterial mating" process known as conjugation. Levy says that too many antibiotics now contaminate our food and water because of drugs given to livestock. Eighty percent of these antibiotics are used because farmers believe they may promote growth, not because animals are sick, he says. In a 4 March 1976 article in Nature, Levy showed how antibiotic-resistant plasmids in chickens could spread to farm workers.
It remains to be seen if the pharmaceutical industry will discover new antibiotics in time to combat resistant bacteria. Levy isn't optimistic, but he admits it may be possible. Daniel Bonner, executive director of microbiology at Bristol-Myers Squibb, points out that oxazolidinones--discovered by DuPont and now being developed by Upjohn Co.--represent a fundamentally new class of antibiotics. In the search for new antibiotics, Levy says, researchers are now investigating chemicals in insects, compounds in frog skin, and components of soil mined from deep beneath the earth's surface. But like existing antibiotics, he cautions, new treatments will soon become obsolete without safeguards to prevent resistance.
Antibiotic resistance is costly; the average cost of treating nonresistant tuberculosis (including drugs, procedures, and hospitalizations) is about $12,000, according to Mitchell L. Cohen, director of the CDC's Division of Bacterial and Mycotic Diseases in an article in the 21 August 1992 issue of Science. For multidrug-resistant tuberculosis cases, he says, costs can soar to $180,000. To help prevent resistance, the American Society for Microbiology states that doctors must be trained to distribute antibiotics appropriately, and patients should be educated about the dangers of "sublethal" doses that fail to kill all of the bacteria and thereby promote resistance.
Pesticides and Disease
Using pesticides to control public health risks "can cause resistance in the very insects they are intended to kill," the IOM report says. The report adds that a "growing array" of pesticides no longer kill mosquitoes that transmit malaria.
According to the report, in 1987 farmers used 407,000 tons of pesticides in the United States. Worldwide, only 10% of all pesticides are used to control public health problems. In 1992, the IOM urged the EPA to develop faster procedures for approving pesticide use in the event of an emergency. The committee also recommended stockpiling designated pesticides to ensure a fast response to outbreaks of diseases such as malaria. Strategies for managing pesticide resistance include the rotation of chemicals, avoidance of sublethal doses, and the use of biodegradable materials.
Despite such efforts, pesticide resistance is a growing problem. A 1986 report published by the National Research Council entitled Pesticide Resistance: Strategies & Tactics for Management, pointed out that only seven species of insects and mites were resistant to insecticides before World War II. By 1984, the report says, at least 447 species were immune to one or more insecticides. Several agricultural pests, including the Colorado potato beetle, were impervious to all known pesticides in 1986.
Crops engineered to resist pests may allow farmers to use fewer chemical pesticides, but some observers say genetically engineered plants might also transfer undesirable traits to neighboring plants. In the 7 March 1996 issue of Nature, researcher Thomas R. Mikkelsen and colleagues from the Riso National Laboratory in Denmark reported the transfer of herbicide-resistance genes from a genetically manipulated rape plant to a weedy relative, Brassica campestris. In response to Mikkelsen's report, a large German environmental organization, BUND, called for a ban on field experiments with bioengineered plants. Meanwhile, some consumer advocates have criticized the Flavr Savr tomato, which is genetically engineered by Calgene, Inc. of Davis, California, to resist rotting. An anti-rotting gene is added to the Flavr Savr's genome using an antibiotic-resistant marker gene. Critics fear the marker gene could increase antibiotic resistance in humans. Levy says, however, that the kanamycin-resistant gene used in processing the Flavr Savr tomato is "one that we don't use much anymore," and it is "millions of times more evident in our own gut flora, compared with its presence in the tomato."
Preparing for the Future
"Humans are not powerless against this relentless march of microbes," wrote Morse in his article in Emerging Infectious Diseases. Improved surveillance and a better understanding of disease can go a long way toward reducing human suffering and health care costs, he added.
A variety of initiatives are under way to prevent epidemics. The CDC's 1994 report calls for improved disease surveillance, applied research, better prevention and control, and a stronger public health infrastructure. Thus far, Ostroff reports, a multiagency task force directed by the CDC has strengthened surveillance by setting up emerging-infections programs to track "high priority diseases" and to analyze health risks in specific communities. The CDC is also providing additional funds to help state health departments respond more effectively to emerging diseases. New electronic networks, for example, will allow state officials to make use of laboratory diagnoses in real time. For example, ProMED--the international Program for Monitoring Emerging Diseases--will provide grassroots surveillance of pubic health problems. (See sidebar article.)
In addition, Ostroff says, "sentinel networks" composed of hospital emergency departments have been formed to identify emerging diseases more promptly. Public health microbiologists receive training through a new fellowship program, he says, and the CDC is "beefing up collaborating World Health Organization [disease] surveillance centers."
In May 1995, WHO identified emerging-disease surveillance as a top priority, reports Lindsay Martinez, a senior program manager in the newly formed Division of Emerging and Other Communicable Diseases Surveillance and Control. The division's key activity is directing a network of laboratories to study antibiotic resistance patterns. "Resistance is an extremely critical problem in the developing world," Martinez says. "When a routine antibiotic for common infections is no longer effective, it's necessary to look to second-line antibiotics, which are usually more expensive and may not be available at all."
The National Aeronautics and Space Administration (NASA), meanwhile, has launched the Global Monitoring and Disease Prediction Program. Using data from satellites and other remote-sensing equipment, NASA is analyzing land-use changes and population demographics to predict outbreaks of Lyme disease, malaria, and other illnesses, says the program's manager, Maurice Averner. NASA is even analyzing the African landscape in search of a nonprimate reservoir, such as a mosquito or tick, that may carry the Ebola virus. Since Ebola victims often lived near charcoal-making pits, Averner explains, surrounding geographic features might help NASA identify the most likely source of the disease.
When antibiotics allowed doctors to triumph temporarily over microbes, "we acted as though we had won the war on infectious disease," says Professor Joshua Lederberg of The Rockefeller University. But, Lederberg notes, "the fact is, infectious microbes have been around all along and will continue to pose threats to public health."
Ginger Pinholster
Microbe photo credits: Ebola, Frederick A. Murphy; HIV, C. D. Fermin and R. F. Garry; Rotavirus, M. Stewart McNulty; Malaria, Blackwell Scientific Publications; Tuberculosis, Edward C. Klatt; Rabies, Frederick A. Murphy; Giardia, James A. Sullivan.
ProMED: A Global Early
Warning System for Disease
"Until we knew there was such a thing as AIDS, there was no [monitoring] system that would recognize it. And if AIDS were to come along today as a new disease, we would still be in the same situation," said Stephen S. Morse, assistant professor of virology at The Rockefeller University in New York City.
Currently, an international group of some 35 senior scientists and health experts who make up the steering committee of the Program for Monitoring Emerging Diseases (ProMED), are working to see that this situation soon changes. ProMED's goal is to provide an effective global system of infectious disease surveillance that could give early warning to public health officials and others of new diseases, as well as of outbreaks of familiar ones.
A project of the nongovernmental policy group Federation of American Scientists (FAS), ProMED had its inception when the Institute of Medicine Committee on Emerging Microbial Threats to Health of the National Academy of Sciences issued its Emerging Infections report in 1992.
According to Morse, who was a member of that committee, "Many people were very concerned that all over the world, the ability to spot even known diseases and identify them properly, and in time to take appropriate action, is very variable." Hence, one of the report's primary recommendations was that steps be taken to fill that void. In response, a meeting, cosponsored by FAS and the World Health Organization, was held in late 1993 and ProMED was born.
To date, the most visible manifestation of ProMED is its e-mail network. Accessible at majordomo@usa.healthnet.org, the network has some 4,500 subscribers from over 100 countries, says Morse, who chairs the ProMED steering committee. ProMED selected e-mail, the most basic Internet technology, as its primary means of communication so that those in developing countries, where the World Wide Web may not yet be available, can participate fully. However, the group also maintains a WWW site, http://www.fas.org/promed, through which its files can be accessed.
Established only two years ago, the e-mail network "has taken off in a way that we are very gratified to see," says Morse. Already it has carried the first report of Japanese encephalitis in Australia. Subscribers have also reported the 1994 deaths of racehorses and their trainer in Australia from the newly identified morbillivirus, the 1995 Ebola outbreak in Zaire, and the 1995 outbreak of avian influenza in Mexico.
But e-mail is only one tool available. A formal international surveillance system must exist on one end of the communications network, with an assessment and response apparatus at the other end for the system to be effective. ProMED is actively working with various organizations to realize these goals.
Victor Chase
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[Table of Contents]
Last Update: June 23, 1997
