HIV stands for human immunodeficiency virus, which can lead to AIDS. It damages the body's immune (defence) system. A virus is a type of germ and HIV affects only humans.

How does the immune system work?

In order to understand AIDS, it is important to understand the basic workings of the immune system. First, consider blood. One major function of blood is protection from infection by foreign agents, and the cells of the blood responsible for this task make up the immune system. The immune system protects us from infectious agents which include viruses, bacteria, protozoa, fungi, and multicellular parasites. Also, the immune system is important in fighting cancer. Cells of the immune system are divided into two classes; those that respond to a specific foreign agent (lymphocytes) and those that are not specific for the agent they attack (phagocytes, mast cells, eosinophils, and natural killer cells). Phagocytes, mast cells, and eosinophils are intructed by antibodies to attact particular cells. Antibodies, proteins produced by certain lymphocytes, bind specifically to a foreign agent or antigen. This allows the phagocytes, mast cells, and eosinophils to recognize the target, and they attack.

Focusing on the lymphocytes which respond to specific antigens (foreign invaders) in the body, the two classes of cells are B-lymphocytes (B-cells) and T-lymphocytes (T-cells). B-lymphocytes are the cells which secrete the antibodies that recognize and bind to specific antigens. Each B-cell makes only one kind of antibody. The body's immune response is based on generation of many B-cells with different antibody specificities and rapid production of B-cells that recognize their specific antigen when infection occurs. Antibodies generated by B-cells fight infections by direct neutralization of viruses, binding to targets and signaling phagocytes or other white blood cells to attack, or binding to target cells and signaling for other host defense mechanisms.

T-cells are similar to antibodies in that they also bind to the surfaces of specific antigens. Unlike B-cells which generate antibodies to bind to the antigens, the T-cells themselves are involved in binding. Tkiller-cells bind to the surfaces of and then eliminate foreign cells. Thelper-cells signal to B-cells or Tkiller-cells and help them to respond to antigens. All T-cells have characteristic proteins on their surfaces: the CD8 protein is present on Tkiller-cells and the CD4 protein is present on Thelper-cells. We will learn more about virus activity shortly, but at this point it is important to point out that, when HIV infection occurs, the virus recognizes and binds to the CD4 protein which is found on Thelper-cells. Eventually, the virus causes these cells to die.

In healthy people, the number of Thelper-cells per cubic millimeter of blood are typically over 1000. In AIDS patients, there may be well under 100 Thelper-cells per cubic millimeter. Currently, a Thelper-cell count of under 200 is used as the defining mark for people with full-blown AIDS. People with a Thelper-count of more than 200 are said to be HIV-infected; people with a Thelper-count of less than 200 are said to have advanced to AIDS.

What is a virus?

Viruses are among the simplest life forms. They are parasites; they cannot replicate and make more of themselves outside of cells. In humans, this means that viruses must replicate in some tissue or cell type in our bodies.

Virus particles consist of just two main components--genetic material and a system for protecting this material and introducing it into a cell (Figure 1). The viral genetic material is carried in the form of either DNA or RNA which are chemically related compounds made of nucleic acids. The genetic material of a virus specifies virus proteins which may be regulatory proteins that help the virus to take over a host cell, structural proteins that help with the growth of the virus particles, or enzymes that help carry out biochemical processes necessary to the virus. Because this genetic material is quite fragile, viruses carry genes that direct production of a protein coat to surround the genetic material. Some viruses also direct synthesis of a viral envelope that surrounds the virus's genetic information and protein coat. For many basic functions including energy metabolism, protein synthesis, and nucleic acid synthesis, viruses depend on cells.

What does HIV positive mean?

When a person becomes infected with HIV the body's immune system tries to fight off the virus by making antibodies. Antibodies are one of the body's lines of defence against infections. If antibodies to HIV have shown up in a blood test, a person is described as HIV positive.

Someone with HIV will be infected for the rest of his or her life. They may look and feel fine, and completely healthy; most people with HIV do. Unless they are tested for antibodies to HIV they may not know they have the virus. You can't tell by looking at someone if they are infected with HIV. They look no different from someone who doesn't have the virus.

What is AIDS?

AIDS stands for Aquired Immune Deficiency Syndrome. AIDS describes the later stages of HIV when a person has a collection of illnesses because their immune system has been damaged as a result of getting HIV.

There is no cure for HIV or AIDS yet, although new drugs and new ways of using existing drugs are constantly improving medical care. Many people live with AIDS for many years and feel well most of the time. Many infections are treatable, although as the body's immune system weakens, infections become more difficult to treat.

How is HIV spread, Transmitted?

Three main ways of passing HIV

HIV is passed from person to person in the following ways, which is called transmission:

·         Blood

·         Semen

·         Vaginal Fluids

·         Breast Milk

·         Pre-ejaculate

Information on HIV frequently changes. We still do not know for sure where the virus came from and we are constantly learning how HIV affects our bodies. New drugs come onto the market regularly and the side effects of these very powerful drugs are not fully known. The information that does remain constant is that of transmission. The important HIV prevention message is: HIV is transmitted through activities, it is not transmitted because of who you are.

The main ways to transmit HIV are:

·         Unprotected sex

·         Sharing drug equipment

·         Blood

·         Mother to baby

Unprotected Sex

Some kinds of sex carry high risks of getting HIV from an infected person. However, it is important to remember that there is no way you yourself can tell if another person is infected or not.

With HIV, safer sex means not allowing your partners blood, semen or fluid from the vagina to get inside your body. Vaginal and anal sex without a condom carry the highest risk - whether male or female.

Always use a condom, even if you have been with your partner long enough that you feel you can trust him/her. The only way to know whether a person has HIV or not is for them to have an HIV test.

Condoms also protect against other sexually transmitted infections and unintended pregnancies.

Other kinds of sex carry either no, or very little, risk of HIV infection. This includes kissing and masturbation. Oral sex carries a small risk, which can be reduced by:

·         avoiding getting semen in the mouth, particularly if there are any cuts, sores or ulcers in the mouth

·         using a condom for oral sex with a man (flavoured varieties are available!)

·         using a latex square - called a dental dam - for oral sex with a woman. Placed over the genital area, it can protect against infection from vaginal fluid and menstrual blood. Dental dams are available from some clinics, chemists, shops and mail-order companies.

Sharing Drug Equipment

HIV can be spread if you share drug injecting equipment - or 'works' - with other people. This can include - syringe, needle, spoon, bowl and water.


Mother and child

There is a risk that a mother with HIV can pass it on to her baby, either in the womb or through breastfeeding. HIV screening for pregnant women is not routine but may be offered.

Some treatments have been shown to reduce the risk of passing HIV to the baby, as have some kinds of delivery. If a woman with HIV has a baby, it can take a few months to know whether or not the baby has the virus too. A doctor or midwife can explain this in more detail.

How HIV is NOT passed on Other risks?

You can't get HIV by:

·         kissing, touching, hugging or shaking hands

·         sharing crockery and cutlery

·         coughing and sneezing

·         contact with toilet seats

·         insect or animal bites

·         swimming pools

·         eating food prepared by someone with HIV.

Other Risks

There are other ways of getting HIV, but these are much lower risk than unprotected vaginal or anal sex.

Giving/receiving blood

There is a very small risk of getting HIV by receiving a blood transfusion in the UK. All blood, blood products, organs and tissues for donation and transplant in the UK are screened for HIV. Also, potential blood donors are asked to complete a questionnaire meaning that the chances of being infected from donation or transplant are minimal.

Donating blood through the blood transfusion service in the UK is completely safe. The equipment used is sterile and only used once.

Doctor/dentist treatment

All healthcare workers in the UK take routine precautions to prevent any risk of any infection to patients. However, outside of the UK, particularly in the developing world and in Eastern Europe, there may be risks from certain medical procedures. Phone the free Healthline on 0500 20 20 30 for information about your specific destination.

First Aid

The best precaution is to avoid any direct contact with the injured person's blood. Use gloves, and follow standard health and safety precautions. If blood gets on your skin, simply wash it off.

Dropped needles

Avoid handling the metal needle. If someone does get pricked by a used needle, pinch the wound to make it bleed a little. Clean the area with soap and water, cover with a plaster, and then seek medical advice.

Skin piercing

Tattooing, ear-piercing, accupuncture and hair removal by electrolysis also pose a risk of passing on HIV and other infections. Only use these services (if you are old enough) where sterile and/or disposable equipment is used. Ask if you are unsure.

The HIV Test?

The 'AIDS Test' as it is commonly known, does not actually test for AIDS. However, there is a test which can show whether or not someone has HIV. The test checks for the antibodies which the body produces to fight off HIV infection.

Most tests are carried out by genito-urinary medicine (GUM) clinics - see 'Help in your area' for contact details.

These clinics offer free tests and all information is strictly confidential. You don't have to use a local clinic or be referred by your GP. If you do ask your GP to organise the test, the result may be entered into your medical records.

The test involves a sample of blood being taken from your arm - the time taken for the results to arrive varies. For more information about HIV tests, contact your GP or GUM clinic.