Microbes – Infectious Diseases
Microbes: Invisible Invaders … Amazing Allies INFECTIOUS DISEASES – 1944-PRESENT
Infectious diseases are mankind’s leading causes of death, killing more than 17 million people worldwide every year. Costs of domestic research by U.S. pharmaceutical companies are estimated to grow to $15 billion this year in an ongoing effort to understand and control infectious diseases–the age-old scourges and some emerging newcomers.
Mankind’s first real victory in the seemingly endless war against infection came in 1943 with the mass production of penicillin. The new “miracle drug” cured diseases once considered serious and even deadly, such as meningitis and pneumonia.
Development of other antibiotics soon followed. The success of antibiotics led to the popular belief that bacterial infections could be cured easily and even eliminated from populations around the world.
Viral infections seemed vulnerable as well. In 1955 Dr. Jonas Salk introduced the first polio vaccine; in 1961 Dr. Albert Sabin introduced a less expensive oral vaccine. After the start of nationwide campaigns with Salk’s vaccination, the incidence of polio in Western Europe and North America dropped from 76,000 in 1955 to less than 1,000 in 1967. Vaccines developed in the 1950s and early ’60s prevented other viral diseases: measles, rubella, influenza.
Another of humanity’s greatest success stories was the eradication of smallpox. In 1980 the World Health Assembly formally announced the elimination of smallpox from the planet, the first–and so far, the only–total victory over any human disease.
As early as the 1960s, the threat of infectious diseases appeared to be receding. In 1967 the national euphoria prompted the U.S. Surgeon General to predict prematurely the imminent demise of infectious diseases.
Over the last two decades, however, post-World War II optimism has been replaced by apprehension. Modern transportation, overcrowding and pollution foster the global spread of infectious diseases at unprecedented rates. Researchers face different challenges: mutant strains of drug-resistant microbes, the appearance of old diseases in new places and newly emerging viruses, bacteria and parasites.
Malaria (Plasmodium protozoan) – Malaria is a common tropical and subtropical disease worldwide. When some mosquito species bite, they spread the protozoan that causes malaria. Symptoms include violent chills, high fevers and sweating; some strains can cause delirium and swelling of the brain. Malaria can be fatal, but most forms can be prevented and treated. The malaria parasite is becoming resistant to commonly used drugs, however. A global eradication program begun in 1958 and abandoned in 1963 actually produced a revival of the disease. Near-eradication caused a lack of immunity. Excessive use of insecticides led to resistant mosquito populations; widespread use of antimalarial drugs created new drug-resistant strains. By 1975 the worldwide incidence of malaria had more than doubled what it had been in 1961. Today malaria leads to more than 1.5 million deaths a year.
Cholera (Vibrio cholerae bacterium) – Cholera hot spots are found in Southeast Asia, Africa, Russia and South America, leading to 100,000 deaths a year in Asia alone. This disease is caused by bacteria that thrive in sewage-polluted water. Cholera causes severe diarrhea that can lead quickly to dehydration and death, especially among children. It is treatable with tetracycline, an antibiotic, although rare drug-resistant strains are increasing.
Old Diseases Reappearing in New Places
Tuberculosis (Mycobacterium tuberculosis bacterium) – TB spreads through the air and occurs throughout the world. Globally nearly 2 billion people are infected; each year, there are 8 million new cases. TB can be fatal, especially if the bacteria causing the disease are among the rare drug-resistant strains that have emerged recently. If not, treatment with a combination of antibiotics usually is effective. Symptoms include fevers, fatigue, weight loss, chest pain and persistent cough.
Dengue fever (Dengue fever virus) – Dengue is a disease of the tropics and subtropics worldwide. It is spread by some mosquito species that carry and transmit the virus when they bite.
Most people recover uneventfully from dengue, despite its painful symptoms: severe headaches, eye pain and achiness of the muscles and joints. Dengue hemorrhagic fever, however, can be fatal. Symptoms include hemorrhagic skin rashes–tiny sites of breakthrough bleeding–and shock. The best prescription against dengue is prevention: proper sewage disposal and mosquito control. Up to 50 million cases of dengue fever are reported worldwide each year.
Emerging Infectious Diseases
AIDS (Human immunodeficiency virus–HIV) – Scientists suspect HIV first was transmitted to humans from African monkeys, but they are not sure. Today the epidemic caused by HIV affects people on every continent. In the U.S., AIDS–a later symptomatic stage of the disease–is the second leading cause of death in the 25- to 44-year-old age group. Symptoms of HIV disease include bouts of life-threatening pneumonia, intractable diarrhea, swollen lymph nodes, fevers, weight loss, meningitis, and “opportunistic” infections–viral, bacterial or fungal. Scientists are now fighting the virus with multi-drug combinations that slow the disease’s progression and may prolong the patient’s life.
Ebola hemorrhagic fever (Ebola virus) – No one is sure where this rare virus came from or where it will strike next. In the past, Sudan, Uganda, Zaire (Congo) and Gabon have experienced Ebola outbreaks. Ebola hemorrhagic fever is almost always fatal. Symptoms include acute diarrhea, severe bleeding, nausea, vomiting, muscle aches, headache and fevers. Researchers are studying those who have survived the disease to find a treatment or cure.
Hantavirus ARDS–acute respiratory distress syndrome (Hantavirus) – This disease was first recognized in 1993 in the southwestern United States. Spread in rodent droppings, this disease is often fatal. Symptoms include fever and muscle aches, followed by respiratory distress and shock. No specific treatment currently exists.
Lyme disease (Borellia burgdorferi bacterium) – Lyme disease is found in many places, from North America and Europe to Japan, China and Australia. The illness is caused by bacteria that spread through the bite of a deer tick. Symptoms include skin rash, meningitis, muscle and joint pain, and arthritic symptoms. Lyme disease is usually not serious if treated early with doxycycline or amoxicillin.
Other Common Infectious Diseases
Many infectious diseases clearly pose major health risks. However, thanks to advancements in developing new vaccines and effective drugs, we have learned to control successfully some common diseases such as influenza, streptococcal infections, measles, mumps, whooping cough, polio and bacterial meningitis. While it is still very important to take appropriate measures to avoid and/or treat these conditions, they are no longer cause for alarm in industrialized countries. These diseases represent victories in scientific research. We are learning how to prevent, treat and cure once-deadly diseases, and through research we will continue to make strides to stay one step ahead of today’s most serious infectious illnesses.
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