Emerging Diseases since 1950
Emerging Diseases since 1950
Emerging diseases, which come in a variety of forms, began to appear just when medical science was confident that scourges like smallpox and polio had been conquered. Emerging diseases include the Marburg virus, which was first recognized in 1967, and its close cousin, the Ebola virus. Both are deadly hemorrhagic diseases for which there is no cure. Equally lethal, the AIDS pandemic and infections from bacteria such as E. coli have sickened and killed many. Moreover, a number of diseases thought to have been under control, such as malaria and cholera, have suddenly increased in their rate of incidence. At the same time, because of increasing resistance to drugs, old conditions are re-emerging. For example, tuberculosis, thought to be under such control that tuberculosis hospitals were phased out, has re-emerged, killing more that two million people each year.
Diseases and plagues have changed the course of history. Historians have theorized that malaria was more responsible for the fall of the Roman Empire than the barbarians. The Black Death, or bubonic plague, ended the institution of feudalism and caused such a general paralysis in the 1300s that countries such as England and France stopped their fighting and called a truce. The Spanish and other Europeans brought diseases to the New World that decimated whole populations of natives.
The influence of pandemics involving diseases such as cholera, typhus, and the Black Death was profound, but attitude and ignorance were also negative forces. This situation began to change in the middle of the nineteenth century with not only the discovery of bacteria and inoculation but with a more humane attitude toward life and health habits. Nevertheless, there were still problems because in a major epidemic, such as the one involving influenza in 1918, physicians were still powerless. In 1941 antibiotic drugs, for the first time, allowed an attack on bacterial organisms once they had invaded the body. The public began to think of medical science as a god able to take care of all ills and problems. At the beginning of 1950, the public attitude in the Western world was that science would cure anything. Plagues would be conquered; there would be no more disease.
Optimism about science continued to build in the 1960s and 1970s. For example, the last case of smallpox, registered in Somalia on October 26, 1977, touted the eradication of the disease. From remote areas of the past, however, began to emerge silent threats—quietly at first because they affected only a few people but then more loudly. With people travelling now more frequently to developing countries and with increased trade, conditions that were once isolated are now being seen in more locations. Few things have piqued the public's imagination more than scenes of zombie-like people dying with the god of medical science unable to intervene.
In 1967 workers in laboratories in Marburg and Frankfurt, Germany, and Belgrade, Yugoslavia, became ill after being exposed to African green monkeys imported for research. While the exact origin of the monkeys is unknown, they appear to have come from Uganda, Kenya, or Zimbabwe. How the monkeys originally got Marburg fever is also unknown, but humans contract it from the animals and then pass it on to other people. The disease is characterized by fever, chills, headaches, and myalgia, or muscle pain. Around the fifth day, the infected person may have nausea, vomiting, or diarrhea, which becomes more severe, leading to massive hemorrhaging and multi-organ dysfunction. The disease is almost always fatal. Many of the initial symptoms, unfortunately, are similar to other diseases, such as malaria and typhoid fever. Laboratory tests, such as ELISA (enzymelinked immunoabsorbent assay) and other procedures, may be used to confirm a diagnosis in about three days. A specific treatment for the disease is not known. Hospitals treat all suspected cases with barrier nursing techniques, which include the use of protective gowns, gloves, masks, and strict isolation of the patient.
Ebola hemorrhagic fever caused a media frenzy in 1976 when it emerged. The disease, named after a river in the Democratic Republic of the Congo (formerly Zaire) is caused by an RNA virus. Since then, there have been a few outbreaks involving identified subtypes: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory Coast. The fourth, Ebola-Reston, appeared in Reston, Virginia, among cymolgous monkeys (from the Philippines) in a research facility. Several workers were infected with the virus but did not become ill.
These viral hemorrhagic fevers (VHFs) are frightening because their origins are unknown and they receive a lot of media attention. These viruses share several common features. VHFs are RNA viruses, which means that they are composed of simple pieces of RNA covered with a tough lipid coat. They have a number of insect hosts; while humans are not the native host, once humans acquire the virus they may pass it on to others. (Contaminated needles or contact with any body fluid may spread the disease.) The emergence of these viruses cannot usually be predicted or controlled. Because more and more people are travelling, these diseases have appeared in places where they have never been seen before. In the first, or index case, the virus is spread through direct contact with blood or body secretions. The symptoms are similar to other diseases, especially at the beginning. Scientists do not know why some people live while most die. Since there is no cure, medical personnel treat the symptoms with transfusions of electrolytes or, sometimes, blood.
Other VHFs have emerged. The Machupo virus, for example, caused hundreds of deaths in Bolivia. In two towns in Nigeria—Lassa and Jos—both natives and foreigners died from the Lassa virus. In fact, this virus was so lethal that researchers in Yale University laboratories stopped work on it.
While many of the emerging diseases have not been traced, hantavirus pulmonary syndrome (HPS) has been found to be carried by rodents, especially the deer mouse. The disease, which appeared in the American Southwest, was traced to exposure to rodent droppings; after one to six weeks, flu-like symptoms with coughing appear. Hospitalization is required but, at present, there is no cure.
Insect vectors may also carry diseases. Lyme disease, for example, is caused by a bacterium carried in the bite of the deer tick. The disease is named after the placed in which it was identified, Lyme, Connecticut. A tell-tale red bull's eye indicates an infected area. If left untreated, the disease may cause serious arthritis-like symptoms. A vaccine for Lyme disease has been developed and approved by the Food and Drug Administration.
The word "encephalitis" means "inflammation of the brain." Many cases of the condition are caused by viruses transmitted by mosquitoes. St. Louis encephalitis (SLE) is found in areas such as Florida where mosquitoes are present. Another example of encephalitis involved a West Nile-like virus in the New York area. Ticks have been found to carry this condition in Asia and Africa but the transmission in New York was probably from mosquitoes feeding on birds infected with the virus. People who live in an area at the time of an outbreak are advised to stay indoors during the early evenings, cover their arms and legs, and apply insect repellent.
Cyclospora, a tiny, one-celled parasite, causes a disease first reported in 1979. Cases began to increase in the mid-1980s. One scare in the 1990s that was related to contaminated raspberries was called a "yuppie" condition because it was traced to luxury hotels that served gourmet dishes. Cyclospora infects the small intestine and causes diarrhea, low-grade fever, and fatigue.
Emerging diseases may be caused by new types of agents, such as prions, which are abnormal proteins that are less soluble and more resistant to enzymes than normal proteins. Prions, although still not completely understood, are known to cause bovine spongiform encephalopathy (BSE), a fatal neurological disorder in cattle sometimes called mad cow disease. BSE has been traced to scrapie, a similar disease found in sheep. Cattle who were fed contaminated sheep meat and bone developed BSE. A panic occurred in September 1997, when 168,000 cases of BSE were found in British cattle. Although the infected cattle were subsequently slaughtered, people worried that many cattle could still harbor the disease. They feared that eating meat from BSE-infected cattle could lead to Creutzfeld-Jakob disease, a rare but always deadly neurological condition. There is no proof that this could happen, but scientists are studying the link, if any, between the two diseases.
Vaccines do not exist for the vast majority of diseases. Scientists hope that when full sequences of viral DNA are deciphered, they be will able to develop prevention and treatment methods. In 1995 scientists completed the first genetic code for a bacterium, Hemophilus influenzae, a major cause of ear infections. By sequencing the genome and comparing it to others, researchers may locate what makes some strains harmless and others virulent. Likewise, this research could lead to the development of antibiotics. Researchers, however, believe sequencing activities have the greatest potential for victory against emerging diseases.
As the twenty-first century arrives, scientists are realizing that our knowledge of disease is never static and that emerging and changing forms of bacteria and viruses are always with us. Add to this equation new diseases such as AIDS and old plagues such as tuberculosis and it is evident that science still has much work to do.
EVELYN B. KELLY
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