The Impact of Microbes on the Environment and Human Activities (page 3)
(This chapter has 4 pages)
© Kenneth Todar, PhD
The primary harmful effects of microbes upon our existence and
civilization is that they are an important cause of disease in animals
and crop plants, and they are agents of spoilage and decomposition of
our foods, textiles and dwellings.
A microbe which is capable of causing infectious disease in an animal
or plant is called a pathogen. Four groups of microbes contain
pathogens: bacteria, fungi, protozoa and the viruses. Only the archaea
and algae are lacking pathogens. Pathogens are the cause of infectious
burgdorferi, the spirochete
that causes Lyme Disease. (R) Influenza virus, cause of flu. CDC.
Historically, infectious diseases are the most significant cause of
death in humans. Until the beginning of the Twentieth Century, it is
estimated that more than half the people who ever lived died from
smallpox, caused by a virus, or malaria, caused by a protozoan.
Bacteria, too, have been the cause of some of the most deadly diseases
and widespread epidemics of human civilization. Bacterial diseases such
as tuberculosis, typhus, plague, diphtheria, typhoid fever, cholera,
dysentery and pneumonia have taken a huge toll on humanity.
Deaths from infectious diseases declined markedly in the United States
during the 20th century. This contributed to the nearly 30-year
increase in life expectancy during this period. In 1900, the three
leading causes of death were pneumonia, tuberculosis (TB), and diarrhea
and enteritis, which (together with diphtheria) caused one third of all
deaths. In 1997, heart disease and cancers accounted for 55% of all
deaths, with 4.5% attributable to pneumonia, influenza, and human
immunodeficiency virus (HIV) infection . However, one of the most
devastating epidemics in human history occurred during the 20th
century: the 1918 influenza pandemic that resulted in 20 million
deaths, including 500,000 in the United States in less than 1 year -
more than have died in as short a time during any war or famine in the
HIV infection, first recognized in 1981, has caused a pandemic that is
still in progress, affecting 33 million people and causing an estimated
13.9 million deaths. This illustrates the volatility of infectious
disease and the unpredictability of disease emergence and points us to
the challenges ahead.
Progress in the 20th century is based on the 19th century discovery of
microorganisms as the cause of many serious diseases (e.g., cholera and
TB). Disease control resulted from improvements in sanitation and
hygiene, the discovery of antibiotics, the implementation of universal
childhood vaccination programs, and technological advances in detecting
and monitoring infectious disease.
of infectious disease as a cause of mortality 1900 to 1996. CDC.
Water purification, immunization (vaccination), and modern antibiotic
therapy (all developments in the field of bacteriology) have
dramatically reduced the morbidity and the mortality of infectious
disease during the Twentieth Century, at least in the developed world
where these are acceptable cultural practices. However, many new
microbial pathogens have been recognized in the past 30 years and
many "old" bacterial pathogens, such as Staphylococcus aureus and Mycobacterium tuberculosis, have
emerged with new forms of virulence and new patterns of resistance to
Microbes are also the cause of many diseases in plants, which, if crop
plants or forest resources, may have important economic or social