Importance of microorganisms to humankind 15

Microorganisms and Disease

Our knowledge of how disease-causing microorganisms (pathogens) spread has permitted us to reduce the incidence of many diseases. Improved sanitation practices, based on our understanding of how disease causing microorganisms are transmitted to humans, have greatly reduced the incidence of diseases such as

plague and gastrointestinal infections. Disinfection of water and proper cooking and handling of foods has greatly reduced the incidence of disease such as typhoid that were once widespread. Sanitary practices in medicine introduced in the latter half of the nineteenth century are now routinely used to protect patients and medical staff against infections (FIG. 1-6).

Some microorganisms can also be used as biological control agents to replace chemical pesticides.

Microorganisms are used to degrade wastes and pol­lutants (FIG. C). Sewage treatment plants, compost piles, and septic tanks use microorganisms to decompose wastes into products that can be accommodated by the environment. Sanitary engineers are important in seeing that these microbial processes run effectively. Mi­croorganisms are also used to bioremediate polluted sites, such as shorelines contaminated by oil spills.

Microorganisms are used in industry to produce an­tibiotics, vaccines, solvents, and numerous other products of economic value (FIG. D). Numerous technicians oversee the daily production operation and ensure the quality of the final product. The biotechnology industry, which uses microorganisms for the production of these products, has been rapidly growing. The ability to ge­netically modify microorganisms now permits the pro­duction of many new products and undoubtedly will lead to the production of many more.

Microorganisms are used to degrade wastes and pollutants to maintain and restore environmental quality. An activated sludge treatment facility has tanks in which microorganisms degrade wastes. Extensive aeration and agitation maintain aer­obic conditions that favor complete degradation of organic compounds by microorganisms.

Microorganisms are grown in fermentors to produce pharma­ceuticals. Small-scale fermentors are used in the research and development phase of pharmaceutical development.

16 CHAPTER 1 UNITY OF THE MICROBIAL WORLD

FIG. 1 -6 A, Florence Nightingale revolutionized nursing practice during the Crimean War when she introduced sanitary practices that help control the spread of infectious diseases. B, Today nurses wear masks, gloves, and gowns during surgery and other medical procedures to prevent infections. C, Surgery is performed in clean operating the­aters that are relatively free of microorganisms.

Importance of microorganisms to humankind 1 7

A mere century ago, 5 of every 10 deaths in the United States were due to microbial infections (FIG. 1.7). Tuberculosis, pneumonia, and gastrointestinal infections were the three leading killers, with diphtheria and bronchitis also listed among the top 10. Today, the only remaining infectious disease caused by microorganisms in this list is pneumonia, a disease that occurs when the defense systems of the body fail—for example, as a consequence of another disease. Although tuberculosis, gastrointestinal infections, bronchitis, and diphtheria still occur, and the number of cases of tuberculosis has recently risen, the percentage of deaths due to these diseases has dropped from over 20% in 1900 to less than 1% of total deaths today.

The reduced mortality from infectious diseases is largely due to the discovery and widespread medical uses of antibiotics and vaccines that have enabled contemporary medicine to reduce the impact of infec­tious diseases. Antibiotics such as penicillin were not available in medical practice until after World War II. They are now routinely used to control microbial in-

Origins of Vaccination

Lady Mary Wortley Montagu, wife of the English ambassador to Turkey (1716-1718), described a crude form of inoculation against smallpox practiced there. In September, old women insert some of "the matter of the best sort of smallpox" into a vein. After 8 days, those so inoculated develop a fever, remain ill for 2 or 3 days, recover within 8 days, and get no pox marks. Lady Montagu tried to persuade the English to adopt this practice, but without success. Edward Jenner got the idea for the technique of vaccination against smallpox from a young girl, a milkmaid it is said, who told him that she would not catch smallpox be­cause she had had cowpox. Jenner is credited with the introduction of vaccination in Europe.

FIG. 1 -7 Mortality due to infectious deseases has declined significantly during the twen­tieth century because of an increased understanding of the roles of microorganisms in hu­man disease and the introduction of practices that reduce the occurrence and effects of mi­crobial infections. Deaths due to many once deadly diseases such as diphtheria, gastroen­teritis, and even tuberculosis are very low (near 0 per 100,000) in the 1990s.

18 CHAPTER 1 UNITY OF THE MICROBIAL WORLD

FIG. 1 -8 A, Smallpox has been eliminated through vacci­nation. The vaccination program that eliminated smallpox began in the 1700s with the work of Lady Mary Montagu and Edward Jenner and became a major effort of the United Nations World Health Organization after World War II. B, Vaccination is used today to prevent many diseases.

fections. Clinical microbiology laboratories assist phy­sicians by rapidly identifying pathogens in infected individuals and determining which antibiotics can be used to control that disease-causing microorganism.

Vaccines are extremely important in preventing disease. An amazing accomplishment of vaccination is the elimination of smallpox. Once 80% of all people on earth could expect to contract smallpox. Now the world is free of this disease. Three centuries of vacci­nation against smallpox and a massive 20-year pub­lic health effort by the World Health Organization finally were victorious over the smallpox virus (FIG. 1-8). The last natural case of smallpox occurred in Somalia, Africa, in 1977. For the first and only time, an infectious disease was eliminated from earth. Effective vaccination programs have also reduced the occurrences of other diseases, such as polio, measles, diphtheria, and whooping cough.

Microbiologists continue to search for new vaccines (substances that stimulate the body's defenses, rendering an individual immune to disease) and antibiotics and to use the techniques of molecular biology to engineer genetically new microorganisms that can produce useful products such as antibiotics and vaccines. Such genetically engineered microorganisms will help meet our future technological needs and improve human health and well-being.

The reduced impact on humankind of diseases caused by microorganisms is due in part to advances in our scientific knowledge of microorganisms and their interactions with humans.

Against the tide of enormous advancement in our understanding of the microorganisms has come the emergence of new infectious diseases, including acquired immunodeficiency syndrome (AIDS). AIDS has shown that diseases caused by microorganisms can still radically change the lives of infected indi­viduals and also of entire societies. Daily, we read in the newspapers, hear on the radio, and see on televi­sion reports about the AIDS virus and other diseases caused by microorganisms. Illness and death spark public concern, and the medical aspects of micro­biology usually are of the most interest to many of us.

So far, scientists have been unable to develop an effective means of preventing AIDS or drugs that will rid patients of the human immunodeficiency virus (HIV) that causes it once an infection occurs (FIG. 1-9). The Centers for Disease Control estimate the incidence of infection with HIV in the United States in 1995 to be 3 in 1,000, with the infection more common in males than females. The World Health Organization estimates that in Africa the incidence in 1995 will be much higher, with 1 in 10 men and women infected with the AIDS causing HIV virus. The cost of treating AIDS patients in New York City alone is running well over $1 billion per year. Only changes in behavioral patterns that reduce the risk of infection with HIV hold any immediate promise for reducing the incidence of this disease. These include the avoidance of unprotected sex with individuals who may carry HIV and avoidance of exposure to contaminated blood through transfusions or shared