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Image“Is it catching?” People sometimes ask this question when they hear that someone is sick. They are talking about a kind of human disease. The kinds of diseases that are contagious (catching) are caused by microscopic germs. Diseases caused by germs are called infectious diseases. Other human diseases can be caused by many things.


Pneumonia, strep throat, and food poisoning are some of the diseases caused by germs called bacteria. Bacteria are living things made of just one cell.

Germs called viruses cause colds, chicken pox, flu, mumps, measles, polio, and AIDS. Viruses are even tinier than bacteria.

A germ called a fungus causes athlete’s foot. Malaria is caused by a germ called a protozoan. Protozoans are made of one cell and are like tiny animals. Mad cow disease may be caused by a strange bit of protein called a prion.


Many germs spread in coughs and sneezes. Sick people get these germs on their hands. You can pick up these germs by touching a doorknob or something else that a sick person touched. Washing your hands regularly can help keep you safe from many diseases caused by germs.

Long ago, many people in Europe and North America died from diseases called cholera and typhoid. The germs that cause these diseases live in dirty water. Good sewers and clean water stopped the spread of these diseases in many countries. These diseases are still a problem in poor countries.


Contact with poisons can cause disease. Smoking tobacco can cause lung cancer and other lung diseases. Drinking lots of alcohol can damage the brain and liver. Lead in drinking water or paint can cause mental problems in children.

Clogged blood vessels cause heart disease. Many older people get diseases caused by body parts wearing out. Arthritis, Parkinson disease, and Alzheimer’s disease are diseases that most often occur as people age.

Sometimes, babies are born with diseases or birth defects. Sometimes babies can inherit (get from their parents) a disease that occurs later in life. Diabetes, high blood pressure, and muscular dystrophy are diseases that people can inherit.

Some diseases are caused by the body’s disease-fighting system. This system is called the immune system. Allergies come from the immune system fighting too much. Touching poison ivy can cause an itchy rash. The rash is a sign of an allergy.

Asthma is a breathing problem caused by the immune system. People can die from a bad asthma attack.

Not eating the right foods can cause disease. Not having enough vitamins can cause some diseases. A lack of vitamin C causes scurvy. Scurvy makes the skin bleed and teeth fall out. Hundreds of years ago, sailors on long voyages often died of scurvy.


Chills and fever are often signs of diseases that are caused by germs. Pain can be a sign of disease. A diseased appendix or other organ causes pain. Itchy eyes and a runny nose can be a sign of hay fever or other allergy. Trouble breathing can be a sign of asthma.

Some diseases have no signs that you can see or feel. You cannot see or feel high blood pressure. Some diseases can only be found during a physical exam by a doctor. It is important to have regular checkups.


Doctors treat many kinds of diseases with medicines. Doctors can kill most disease-causing bacteria with drugs called antibiotics. Doctors give drugs to lower high blood pressure.

Doctors cannot really cure diseases caused by viruses. Your body can fight off colds and flu. The body cannot fight off AIDS, polio, and some other diseases caused by viruses. Doctors have drugs that can slow the AIDS virus. Doctors can vaccinate you against some diseases caused by viruses. Vaccinations help your body fight off disease. There are vaccines against chicken pox, flu, measles, polio, and some other viruses.

Doctors treat some diseases with surgery. They use surgery to take out diseased organs or tumors.

Some diseases doctors cannot yet cure or even treat. Researchers in laboratories are looking for ways to help people with these diseases.

Doctors tell people it is best to keep from getting diseases. Getting plenty of sleep and exercise and eating the right foods can help keep you healthy.

Source: Microsoft ® Encarta