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Infectious Disease

Diseases are caused by pathogens that invade a host body.

Pathogens need a host in order to survive and multiply.

Some examples of pathogens are bacteria, viruses, and

fungi. They can spread through direct body contact,

body fluids, and contact with an object that an infected

person has touched (some viruses, like the common cold

virus, can exist outside the body for a brief period before

they get passed on to another host). Tuberculosis is also

an infectious disease. Victims of tuberculosis cough up

blood from their lungs. Treatment and vaccines for

tuberculosis exist, and this disease has been almost elim￾inated in some parts of the world. However, the total

number of people in the world infected with tuberculo￾sis keeps growing.

Noninfectious Disease

If the disease cannot spread from person to person, then

it is considered noninfectious. Two examples of nonin￾fectious diseases are cancer and heart disease. Here are

some characteristics of noninfectious diseases:

■ They do not transfer from person to person.

■ They are not caused by viruses, bacteria, or fungi.

■ They are sometimes hereditary—meaning that

they are associated with genes and run in

families.

Noninfectious diseases can be classified further:

■ Hereditary diseases. Hereditary diseases are

caused by genetic disorders passed down from

previous generations. Since they are inherited,

they are more difficult to treat because they are a

part of the body’s genetic makeup.

■ Age-related diseases. Some diseases will start to

develop as the body gets older. As the body grows

old, it does not work as efficiently to battle rou￾tine diseases and degenerative diseases such as

Alzheimer’s disease—which causes mild to severe

memory loss or distortion, forgetfulness, anxiety,

and aggressive behavior.

■ Environmentally induced diseases. An environ￾ment that has been polluted with toxins and haz￾ardous waste can affect the population living in

or around it. Radiation from toxic waste can

cause cancer. Exposure to asbestos can lead to

serious lung problems.

Staying healthy by caring for the body is important in

fighting and preventing disease. Poor hygiene and

unhealthy living conditions are invitations for disease.

Here are a few tips to stay healthy:

■ Eat a nutritious diet.

■ Keep your hands and body clean.

■ Exercise regularly.

■ Reduce stress.

■ Don’t smoke.

■ Don’t drink excessively.

It is also important to feel good about yourself. A pos￾itive view of who you are and what you look like can help

reduce stress considerably.

Looking for Symptoms

Before diagnosing a patient with a disease, a doctor looks

for the telltale symptoms. Every disease has specific

symptoms that cause different reactions in the body.

Some of the more common symptoms are fever, nausea,

and pain. A doctor is trained to look for these symptoms

to give a correct diagnosis and issue proper treatment.

Blood tests and X-rays are special methods used to diag￾nose some diseases.

Epidemics

An epidemic is a disease that has infected a considerable

portion of the population and that continues to spread

rapidly. Epidemics can occur when there is no medicine

for the disease, when diseases develop a resistance to

medicine and drugs, or when environmental conditions

are favorable for a specific type of disease. For example,

cancer is rampant in areas with toxic chemicals and high

levels of radiation. Autoimmune deficiency syndrome, or

AIDS, which is caused by the HIV virus, is an epidemic

that is killing millions of people worldwide. HIV is

spread through sexual contact and through contact with

the blood of an infected person.

Natural and Medical Defenses

Humans and most other living beings have a natural

built-in disease-fighting mechanism known as the

immune system. The immune system is composed of

cells, molecules, and organs that defend the body against

pathogens. The immune system is responsible for find￾ing the pathogen in the body and killing it, rendering it

harmless, or expelling it from the body.

–PERSONAL AND SOCIAL PERSPECTIVES IN SCIENCE–

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