What Type of Organisms Live in Our Body & Cause Some Degree of Harm?

The human body can be home to many different types of organism, from the microscopic to parasites that can be seen by the naked eye. The organisms that cause disease may normally live on or in the body, or they may infect the body at some point and stay alive for years.

Gastrointestinal Commensal Flora

• Humans have bacteria in their digestive system to help break down food and convert it into nutrients and they also have fungi and bacteria growing in other parts of the gastrointestinal tract, such as the mouth, the throat and the vagina. Organisms such as these are known as commensals, as they usually do no harm to their host and are healthy to have. <br /><br /><br /><br />Areas of the body such as the internal organs, blood and lower respiratory tract of the lungs do not usually contain any organisms. Although the rest of the body might be populated by microorganisms causing no harm, sometimes the microorganisms end up somewhere they shouldn't be. ??For example, the bacterium Haemophilus influenzae can live quietly in the throat and only cause disease when it gets into the lungs. A fungus called Candida usually lives on the membranes of the vagina safely, but if antibiotics kill off the organisms that live along with it, Candida can grow out of control and cause thrush.

Skin Commensal Flora

• Bacteria such as Staphylococcus species usually live harmlessly on the skin. If the skin becomes broken, the bacterial species can get under the outer protective layer of the skin and form an infection. For example, the species Staphylococcus aureus lives on about three out of ten people. It can potentially cause diseases such as abscesses, blood poisoning and toxic shock syndrome.

Latent Infections

• Some microorganisms can infect a person and remain live in the body for years or for a lifetime. For example, the virus that causes cold sores, known as herpes simplex, can retreat to nerve cells between attacks and stay dormant for a lifetime. Chickenpox is another virus that infects someone when he is young and then hides out in the nerve cells, reactivating in some people many years later to cause shingles. The hepatitis C virus can stay hidden for decades before causing liver cirrhosis or liver cancer.

Parasites

• Parasites can live in the body for years without causing recognizable disease. For example, the United Nations Children's Fund estimated in 2002 that more than three billion people worldwide were infected with roundworm, hookworm or whipworm. The worms do not cause acute disease but can stunt the growth of children, produce chronic diarrhea or result in anemia.