Human
Disease
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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