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It's normal to have many different germs. You probably have some kinds of viruses, fungi and bacteria in your body. If you have a healthy immune system, you can easily control these germs and stay healthy. But if you have HIV, your immune system is damaged. So you aren't as well protected against infections. If you don't keep these infections under control, they can make you sick.

The infections that you get when you have a weak immune system are called opportunistic infections. You can also get some types of cancer if your immune system is weak. If you have HIV and get one of these infections or types of cancer then doctors say you have AIDS.¹

Many opportunistic infections can be serious. And some can kill. But modern treatments that keep HIV under control are making this less likely. In the past, people with AIDS were likely to get a serious infection called Pneumocystis carinii pneumonia (or PCP for short). Many people with AIDS died of this condition. But PCP can now often be prevented and has become less common. The same is true for most of the other opportunistic infections.

If your immune system has been weakened by HIV, there are treatments that can reduce your chances of getting these infections.

Some common infections and types of cancer are:

• Cytomegalovirus infection (CMV): A viral infection that damages your eyes.
• Mycobacterium avium complex infection (MAC): A serious disease caused by common bacteria. MAC can cause diarrhea and loss of weight.
• Pneumocystis carinii pneumonia (PCP): An infection that can cause pneumonia.
• Herpes: This can be cold sores in your mouth or small, painful blisters around your genital area. Both are caused by a virus.
• Toxoplasmosis: An infection of the brain. It can cause fever, rashes and a cough. It's sometimes called "toxo" for short.
• Tuberculosis (TB): An infection that harms your lungs.
• Fungal diseases, such as candidiasis (thrush), cryptococcal meningitis and histoplasmosis: These are yeast infections that usually affect your mouth, brain or lungs.
• Shingles: This is caused by the same virus that causes chickenpox.
• Kaposi's sarcoma: This is a type of cancer that grows in the lining of some blood vessels. It causes purple or black blotches on your skin and inside your mouth.
• Human papillomavirus infection (HPV): This is a virus infection that can cause cancer in the anus or cervix (neck of a woman's womb).
• Lymphoma: This is a type of cancer that affects your lymphatic system, the network of tubes that helps your body fight infections.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.