Diseases Essay, Research Paper

Diseases are 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 has been affected by economic

conditions, wars, and natural disasters. 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: communicable and noncommunicable. Communicable

diseases can spread from one person to another and are caused by

microscopic organisms that invade the body. Noncommunicable 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, and come on suddenly and last for no more than a few weeks. Other

diseases, such as arthritis, are chronic, consistent for months or

years, or reoccur frequently.

Every disease has certain characteristic effects on the body.

Some of these effects, include fever, inflammation, pain,

fatigue, dizziness, nausea, and rashes, are evident to the patient.

These symptoms offer important clues that help doctors and other health

care professionals make a diagnosis. Many times, 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.

Communicable diseases are caused by microscopic organisms.

Physicians refer to these disease-causing organisms as

pathogens. Pathogens that infect humans include a wide variety of

bacteria, viruses, fungi, protozoans, and parasitic worms. Also, it

has been theorized that some proteins called prions may cause

infectious diseases.

Bacteria are microscopic single-celled organisms at least 1

micron long. Some bacteria species are harmless to humans, many

are beneficial. But some are pathogens, including those that cause

cholera, diphtheria, leprosy, plague, pneumonia, strep throat, tetanus,

tuberculosis, and typhoid fever. The bacteria that are harmless and

live in or on you are called resident bateria.

Viruses are tens or hundreds of times smaller than bacteria.

They are not cellular, but consist of a core of genetic

material surrounded by a protective coat of protein. Viruses are able

to survive and reproduce only in the living cells of a host. Once a

virus invades a living cell, it directs the cell to make new virus

particles. These new viruses are released into the surrounding tissues,

and seek out new cells to infect. The roll call of human diseases

caused by viruses includes mumps, measles, influenza, rabies,

hepatitis, poliomyelitis, smallpox, AIDS, and certain types of cancer.

Fungi are a varied group of generally small organisms that get

their food from living or dead organic matter. They germinate

from reproductive cells called spores, which often have a thick,

resistant outer coat that protects against unfavorable environmental

conditions. This enables spores to survive for long periods of time,

which adds to the difficulty of treating fungal infections. Some fungi

are external parasites of humans, causing skin conditions such as

ringworm, athlete’s foot, and jock itch. Other fungi invade internal

tissues. Examples include yeast that infect the genital tract and

several fungi species that cause a type of pneumonia.

Protozoans are single-celled, animal-like organisms that live

in moist environments. The most infamous pathogenic protozoans

are species of the genus Plasmodium, which cause malaria, an infectious

disease responsible for over 2 million deaths worldwide each year.

Members of the genus Trypanosoma produce trypanosomiasis, also known as

African sleeping sickness, and Chagas’ disease. Other protozoans cause

giardiasis, leishmaniasis, and toxoplasmosis.

Some pathogens are spread from one person to another by direct

contact. They leave the first person through body openings,

mucous membranes, and skin wounds, and they enter the second person

through similar channels. The viruses that cause respiratory diseases

such as influenza and the common cold are spread in moisture droplets

when an infected person coughs or sneezes. A hand that was used to

cover the mouth while coughing contains viruses that may be passed to

doorknobs, so that the next person to touch the doorknob has a chance

of picking up the infectious agent. The bacteria that cause some

sexually transmitted diseases, including gonorrhea and syphilis, are

transmitted during sexual contact.

Other pathogens involve an intermediary carrier, such as an

insect. The malarial parasite, for example, spends part of its

life cycle in mosquitoes, then enters a person’s bloodstream when the

mosquito bites the person. Many pathogens are spread through

contaminated food and water. Other pathogens can be passed on by

contaminated food or water.

Noncommunicable diseases not known to be caused by infectious

agents include the three leading killers in the United States

and other developed countries: heart disease, most cancers, and

cerebrovascular disease. Noncommunicable illnesses include disorders

as terrifying as Alzheimer’s disease, which robs victims of their

memory and their ability to reason, and as pesky as poison ivy.

Degenerative disorders, including arthritis, Parkinson’s

disease, and Alzheimer’s disease, involve the progressive

breakdown of tissues and loss of function of parts of the body. Joints

gradually become stiff; bones become brittle; blood vessels become

blocked by deposits of fat. The incidence of these problems increases

with age, and, in at least some cases, progression can be slowed by

good health habits.

There are many ways to prevent these diseases. The skin and

mucous membranes form the body’s first line of defense against

disease. Most microscopic pathogens, or microbes, cannot pass through

unbroken skin, although they can easily enter through cuts and other

wounds. Mucous membranes protect internal organs that are connected

with the outside of the body. These membranes, which line the

respiratory, digestive, urinary, and reproductive tracts, secrete

mucus, which traps microbes. The mucus may then be expelled from the

body, perhaps in a cough or sneeze or in feces. If the mucus is

swallowed, digestive juices kill the microbes.

Small hairlike projections on the lining of the nose, throat,

and bronchial tubes work in conjunction with mucus to trap and

remove foreign substances. In the ears, tiny hairs plus a sticky wax

defend against the entry of germs. Tears secreted by the lachrymal

gland wash away germs and other small objects that may enter the lid

area of the eye. Tears also contain a protein that kills certain

germs.

If a pathogen breaks through the body^s outer barriers, the

defenses of the immune system spring into action. Some of these

defenses are effective against a variety of invaders, while others are

formed to fight a specific organism. White blood cells called

phagocytes constantly travel through the bloodstream on the lookout for

foreign objects. If they come upon a microorganism, they surround,

engulf, and digest it.

During the 20th century, the importance of vitamins and other

nutrients in preventing disease was recognized. Antibiotics,

sulfa drugs, blood types, and genes that cause disease were discovered.

A host of diagnostic and surgical tools were created that incorporated

inventions such as X rays, fiber optics, lasers, and computers.

Techniques such as organ transplantation, kidney dialysis, dental

implants, gene therapy, and fetal surgeries were introduced. Thousands

of new drugs were developed to treat everything from ulcers to zinc

malabsorption.

At the beginning of the 20th century, people in the United

States had an average life span of about 50 years. By the time

the century neared its close, average life span had risen to 76 years.

Other developed countries experienced similar increases. Much of the

credit for these longer life spans, and for the good health that

accompanies them, is due to the conquering of diseases, thanks to

vaccines, antibiotics, sophisticated surgical tools, and other medical

miracles. The challenges ahead include bringing the benefits of this

medical knowledge to all peoples of the world, and expanding on current

knowledge in order to understand, treat, and prevent the diseases that

still confront us.