Human
Disease books
Human
Disease, in medicine, any harmful change that interferes
with the normal appearance, structure, or function of
the body or any of its parts. Since time immemorial,
disease has played a role in the history of societies.
It has affected-and been affected by-economic conditions,
wars, and natural disasters. Indeed, the impact of disease
can be far greater than better-known calamities. An
epidemic of influenza that swept the globe in 1918 killed
between 20 million and 40 million people. Within a few
months, more than 500,000 Americans died-more than were
killed during World War I (1914-1918), World War II
(1939-1945), the Korean War (1950-1953), and the Vietnam
War (1959-1975) combined.
Diseases have diverse causes, which can be classified
into two broad groups: infectious and noninfectious.
Infectious diseases can spread from one person to another
and are caused by microscopic organisms that invade
the body. Noninfectious diseases are not communicated
from person to person and do not have, or are not known
to involve, infectious agents. Some diseases, such as
the common cold, are acute, coming on suddenly and lasting
for no more than a few weeks. Other diseases, such as
arthritis, are chronic, persisting for months or years,
or recurring frequently.
Every disease has certain characteristic effects on
the body. Some of these effects, called symptoms and
signs, include fever, inflammation, pain, fatigue, dizziness,
nausea, and rashes, and are readily apparent to the
patient. These symptoms offer important clues that help
physicians and other health care professionals make
a diagnosis. Many times, however, the symptoms point
to several possible disorders. In those cases, doctors
rely on medical tests, such as blood examinations and
X rays, to confirm the diagnosis.
The course of a disease-that is, the path it follows
from onset to end-can vary tremendously, depending largely
on the individual and the treatment he or she receives.
For example, otherwise healthy people usually recover
quickly from a bout of pneumonia if given proper treatment,
whereas pneumonia often proves fatal to people with
a weakened immune system and to those who do not receive
prompt, effective treatment. Some diseases run a different
course depending on the patient’s age. Chicken
pox, for instance, is usually mild in childhood but
severe in adults. In the United States, only about 5
percent of chicken pox cases occur in people over the
age of 20, but these cases account for 50 percent of
all deaths from the disease
Scientists, public health officials, and other members
of the medical community work diligently to try to prevent
disease epidemics. The battle is constant and is fought
on many fronts. There have been many victories. Once-devastating
diseases such as smallpox and diphtheria have been virtually
eradicated, and many other diseases that once conferred
automatic death sentences can now be either cured or
controlled. At the same time, however, new killers have
emerged. Acquired immunodeficiency syndrome (AIDS) and
hantavirus pulmonary syndrome are among at least 30
diseases that have been identified by scientists since
the early 1970s. Other growing challenges, particularly
in the affluent societies of industrialized nations,
are so-called diseases of choice, such as alcohol abuse,
drug abuse, or obesity, that result from addictive behavior,
poor eating habits, or insufficient exercise.
Complicating matters further are societal changes. Increased
international travel accelerates the spread of both
new and old diseases: A person infected with an unusual
virus on one continent can arrive-with the virus-on
another continent in a matter of hours. Ships, planes,
and trucks can transport disease-carrying organisms
just as easily. In 1985 tires imported into Texas from
Asia carried larvae of the Asian tiger mosquito, which
is a carrier of dengue fever and other tropical diseases.
Within five years, Asian tiger mosquitoes were living
in 17 states. Changing dietary habits and the availability
in local supermarkets of foods from all parts of the
world contribute to an increase in food-borne illnesses.
Some researchers worry that growing populations and
the resulting crowded living conditions will increase
the risk of epidemics
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