Helicobacter Pylori Infection (Peptic Ulcer Disease)

For years scientists and doctors thought that stomach and intestinal ulcers were caused by stress, eating spicy foods, or drinking too much alcohol. But in 1982 two Australian doctors, Barry Marshall and Robin Warren, discovered that H.

Hepatitis, Infectious

The liver plays many important roles in the body. It filters out toxins* and other harmful substances from the blood, stores vitamins and nutrients, regulates cholesterol* production, and helps in the production of many other substances the body needs to function normally.

Herpes Simplex Virus Infections

There are two types of the herpes simplex virus (HSV): HSV-1 and HSV-2. Both are part of the herpesvirus (her-peez-VY-rus) family, a group of viruses with similar traits that also includes the varicella zoster (var-uh-SEH-luh ZOS-ter) virus, which causes chicken pox, and the Epstein-Barr (EP-steen BAR) virus, which causes infectious mononucleosis.

Immune Deficiencies

Immune deficiencies arise when one or more of the parts of the immune system are missing or not working correctly, leaving the body less able to fight disease-causing agents. There are two types of these deficiencies: primary, or inherited, immune deficiencies and secondary, or acquired, immune deficiencies.


The respiratory infection influenza, commonly known as the flu, causes symptoms that include fever, muscle aches, sore throat, and a cough. Once inhaled, flu germs quickly multiply and take over healthy cells.

Intestinal Infections

Viruses, bacteria, parasites, or other pathogens (PAH-tho-jens, microscopic organisms that cause disease) can cause infections in the stomach and small and large intestines, which often lead to gastroenteritis.

Intestinal Parasites

In humans, three types of intestinal parasites may live in the small and large intestines: tapeworms, roundworms (or nematodes, NEE-muh-todes), and protozoa (pro-tuh-ZOH-uh). Certain types remain in the intestines; others travel outside the intestines to invade other organs.

Kawasaki Disease

For children in the United States, Kawasaki disease is the leading cause of acquired heart disease, that is, heart disease that is not present at birth but develops later in life. In 1967, the Japanese pediatrician Tomisaku Kawasaki first described the illness.


The vocal cords are the two bands of muscle found inside the larynx (LAIR-inks), or voice box, located between the base of the tongue and the top of the trachea*. As they let air into and out of the lungs, the vocal cords are relaxed.

Legionnaire's Disease

In 1976 more than 200 people attending an American Legion convention at the Bellevue-Stratford Hotel in Philadelphia, Pennsylvania, suddenly came down with a mysterious illness that caused high fever, chills, and a cough. Thirty-four people died from severe pneumonia.


The disease occurs when a person becomes infected with any of several types of Leishmania parasites*. They spread to people through the bite of female sand flies and can cause different forms of illness, all of which are called leishmaniasis.


His equipment was inadequate and his colleagues thought his theories were laughable. Still, Gerhard Henrik Armauer Hansen (1841-1912) spent day after day bent over his microscope, determined to prove that leprosy was caused by bacteria.

Lyme Disease

Lyme disease was first described in 1977 when a group of children in and around Lyme, Connecticut, became ill with arthritis. In its early stage, Lyme disease produces flulike symptoms; if untreated, the disease can progress to affect the joints, heart, and nervous system, especially in adults.


Malaria, which literally means bad air, was once thought to be spread in the air around stagnant marshes. It is now known that mosquitoes, particularly female Anopheles (a-NOH-fel-eez) mosquitoes, spread the parasites that cause malaria.

Measles (Rubeola)

*respiratory system, or respiratory tract, includes the nose, mouth, throat, and lungs. It is the pathway through which air and gases are transported down into the lungs and back out of the body.


Meningitis is an inflammation of the meninges, the membranes that enclose and protect the brain and the spinal cord. It is usually caused by infection, most often with viruses or bacteria.

Mononucleosis, Infectious

By the time they are 40, as many as 95 percent of adults in the United States have evidence in their blood of a previous EBV infection. Many of these infections are never recognized, especially if they occur in early childhood, because the symptoms look like those of other childhood viral illnesses.


Mumps is an infection caused by a virus. The mumps virus can infect various parts of the human body but typically attacks the salivary glands.

Mycobacterial Infections, Atypical

Atypical mycobacteria are commonly found in the environment, like in soil and water, and in food. Most of the time they do not cause infection or illness in healthy people.

Mycoplasma Infections

Scientists have identified at least 16 species of these tiny bacteria; three have been linked to disease in humans, and researchers are looking at possible relationships between other species and a variety of diseases.