Do Infectious Diseases Pose a Serious Threat? | Introduction
Microbes have existed for hundreds of millions of years, occupying every conceivable ecological niche on Earth. The vast majority are essential to animal and plant life. However, a minority of microbes, defined as pathogenic, cause acute infectious disease or trigger chronic disease in humans. Historically, the consequences have been devastating—medieval plague epidemics killed one-third of the population of Europe, and at the start of the twentieth century tuberculosis, diarrheal diseases, and pneumonia caused 30 percent of all deaths in the United States.
Twentieth-century technological, medical, and public health advances, hailed as “magic bullets,” seemed to promise an end to this threat to human health. Improvements in urban sanitation, cleaner water supplies, and especially the introduction of antibiotics and vaccines led to predictions that the scourge of infectious disease was at an end. Indeed, the World Health Organization declared the eradication of smallpox in 1980. In the United States annual deaths from infectious disease had dropped from 797 to 36 per 100,000 persons and the average life expectancy had increased from 47 in 1900 to 76 in 1980.
A 2003 report by the Institute of Medicine of the National Academy of Sciences outlines policy changes in the United States stemming from such exhilarating success:
As a result of this apparent reprieve from infectious diseases, the United States government moved research funding away from infectious disease toward the “new dimensions” of public health—noncommunicable diseases such as heart disease and lung cancer. The government closed “virtually every tropical and infectious disease outpost run by the U.S. military and Public Health Service.” . . . Infectious disease surveillance and control activities were deemphasized. Research, development, and production of new antibiotics and vaccines declined. The potentially devastating impact of infectious diseases was either relegated to the memory of previous generations or left to the imagination of sciencefiction enthusiasts. Americans could all look forward to long, healthy lives, free from infectious disease . . . or could they?
Unfortunately, they could not. Since 1980, optimistic scenarios have been replaced by grim statistics, particularly in developing countries. The World Health Organization reports that today infectious disease is responsible for half of all deaths in developing countries, and is the leading cause of death in children and young adults. Worldwide, 90 percent of infectious disease deaths are due to respiratory infections, AIDS, diarrheal diseases, tuberculosis, malaria, and measles. Moreover, more than thirty previously unknown or reemerging infectious diseases have been identified since 1970. Public health agencies and medical researchers are raising alarms about the worsening threat of infectious diseases and the inadequacy of resources to combat the threat.
According to medical researchers and epidemiologists, a number of factors make the present-day control and treatment of infectious diseases extremely difficult. Many of these factors played a role in the 2003 outbreak of severe acute respiratory syndrome, or SARS, the first severe, easily transmissible new infectious disease of the twenty-first century and a good example of the challenges posed by infectious disease in the modern world.
First, human encroachment into undeveloped regions, for living space and for natural resources, exposes people to previously unidentified microbes against which they have no immunity. In particular, animal-tohuman transmission of microbes that are not harmful to their animal hosts but may be lethal to humans has been cited as a major source of emerging diseases. Researchers believe SARS originated in remote areas of China’s Guangdong province, where exotic-animal dealers capture civet cats for Chinese urban markets. A strain of the SARS virus has been identified in civet cats, and species jumping is suspected.
The spread of infectious disease originating in animal species depends not only on how easily animals transmit the microbe to humans but also on how easily one infected human can transmit the microbe to another human. That likelihood has increased exponentially because of modern patterns of rapid transportation and increasing population density. Agricultural goods and people now cross the globe in a matter of hours, and international travel has become more affordable than ever before. Thus in a mobile, interconnected world, pathogens can be spread quickly, especially if there is a long incubation period before symptoms appear. In the spring of 2003 the average incubation period for the SARS virus was only two to seven days, and yet failure to identify and quarantine infected individuals has been blamed for the spread of the disease from China to Vietnam to Singapore to Canada, and ultimately to six continents, in a matter of three months. SARS spread most rapidly in big cities; logically, the risk of infection is higher wherever a single infected person may come in contact with hundreds of other people every day.
In the case of emerging diseases, rapid transmission hampers the medical response simply because it is time-consuming, costly, and difficult to diagnose an unknown pathogen and begin effective treatment, if indeed effective treatment exists. The diagnosis of SARS was a success story. The first clinical cases of SARS appeared in China in November 2002, but SARS did not attract international attention until its severity and transmissibility were recognized in March 2003. Confirmed diagnosis of the coronavirus that causes SARS came in mid-April, along with news that effective antibiotics existed to combat the disease. Diagnosis was not simple, however; the early symptoms of SARS mimic harmless flulike symptoms for which most people are not likely to seek medical attention, raising fears that very dangerous diseases such as SARS may go unnoticed until it is too late to control their spread.
The existence of effective drugs to treat SARS was atypical. Researchers point to a dwindling number of effective drug treatments and a lack of preventive vaccines as a major factor in the growing threat of infectious diseases. There are no vaccines for the host of emerging diseases identified since 1980, including AIDS, tuberculosis, and malaria, pandemics that together account for 500 million illnesses a year and at least 6 million deaths. Moreover, recent awareness of biological agents as possible weapons of terrorism has focused attention on public vulnerability to smallpox. The last smallpox vaccination program in the United States, for example, ended in 1972; immunity to the disease wears off approximately ten years after vaccination, and since the September 11, 2001, terrorist attacks the U.S. government has scrambled to make enough smallpox vaccine to reimmunize the general public in case of a biological attack.
The biggest treatment-related problem concerns growing microbial resistance to existing antibiotics. Through natural mutation and overuse of antibiotics, which encourages the growth of resistant strains of pathogens, many microbes once destroyed by a wide range of drugs are now resistant to all known antibiotics. According to a 1997 Institute of Medicine study, in the United States up to 35 percent of Streptococcus pneumonia infections are resistant to penicillin, 32 percent of Staphylococcus aureus infections do not respond to the once-powerful antibiotic methicillin, and 13 percent of tuberculosis infections are resistant to all drug therapies.
Critics charge that the world’s public health infrastructures, under scrutiny as epidemics rage, are too weak to respond effectively to infectious disease outbreaks. Electronic reporting systems and databases have been instrumental in tracking the spread of disease, but containing and controlling disease is much more challenging to underfunded, underequipped public health agencies, especially where political instability or censorship restricts the timely spread of information.
In 2003, for example, Chinese public health officials at first failed to release news of SARS to the Chinese public, failed to accurately report cases of SARS to international health agencies, and failed to take steps to protect health-care workers in time to prevent additional infections. In turn, immigration controls failed to identify those who had contact with sick people in time to prevent them from exposing others across international borders. In affected countries, sketchy news of a new, deadly epidemic fueled signs of public hysteria—thousands, for example, began wearing face masks—and media exaggeration.
Eventually, with quarantine measures and prompt treatment, the SARS epidemic subsided in the summer of 2003. Public health agencies taking stock of their ability to respond to infectious diseases also tried to prepare for future SARS outbreaks, which some researchers suggest are likely to occur seasonally, like influenza. Generally that assessment has been followed by requests for increased government funding to buy drugs, increases in staff, strengthened laboratory and epidemiological capacities, and public-information campaigns.
Where the next major outbreaks will occur, how to apply resources most effectively to treat current epidemics, and how to reduce the threat of infectious disease are subjects of intense debate. The articles in At Issue: Do Infectious Diseases Pose a Serious Threat? examine the scope of the problem. Meanwhile, China reported in January 2004 the first three cases of a new outbreak of SARS.
