HIV and AIDS: Cause, Transmission, Symptoms and Treatment

1Why this matters

Few diseases have changed Africa as much as HIV. In the 1990s an HIV diagnosis usually meant death within a few years. Today, a person who is diagnosed early and takes treatment every day can expect a long and healthy life, and can have children who are free of HIV. Rwanda has hundreds of thousands of people living with HIV, most of them on treatment. Knowing the biology of HIV helps you protect yourself, and helps you replace fear with facts.

2What HIV is

HIV stands for human immunodeficiency virus. It is a retrovirus: its genes are made of RNA, and it carries an enzyme, reverse transcriptase, that makes a DNA copy of those genes once it is inside a human cell. This DNA copy is inserted into the cell's own DNA. There it can stay hidden for years, which is why no medicine can yet remove HIV completely from the body.

HIV attacks helper T cells, also called CD4 cells because they carry a surface protein called CD4, which the virus uses to attach. As you learned in unit 11, helper T cells coordinate the whole adaptive immune response. As HIV destroys them, the immune system slowly loses its ability to fight infections.

3AIDS

AIDS stands for acquired immunodeficiency syndrome. It is the late stage of HIV infection. A healthy person has about 500 to 1,500 CD4 cells in every microlitre of blood. A person with HIV is diagnosed with AIDS when the CD4 count falls below 200 cells per microlitre, or when they develop certain serious infections. These are called opportunistic infections because they take the opportunity of a weakened immune system; they include tuberculosis, a type of pneumonia, severe fungal infections such as thrush, and a skin cancer called Kaposi's sarcoma.

4The stages of HIV infection without treatment

1. Acute infection (2 to 4 weeks after infection): some people have a short, flu-like illness. The amount of virus in the blood is very high, so the person is very infectious, often without knowing they have HIV.
2. Clinical latency (often 10 years or more): usually no symptoms, but the virus keeps multiplying and the CD4 count slowly falls. The person can pass HIV on.
3. AIDS: the CD4 count falls below 200, and signs appear: great weight loss, fevers and night sweats that keep coming back, diarrhoea lasting weeks, swollen glands, and repeated infections. Without treatment, a person with AIDS usually survives about three years.

5How HIV is and is not transmitted

HIV is found in large enough amounts to infect someone in blood, semen (including the fluid released before ejaculation), vaginal fluids and breast milk. It passes on through:

• unprotected sexual intercourse with an infected person;
• sharing needles, syringes, razor blades or other instruments that break the skin;
• from mother to baby during pregnancy, birth or breastfeeding;
• transfusion of infected blood (in Rwanda, all donated blood is tested).

HIV is not passed on by hugging, shaking hands, sharing cups, plates or food, using the same toilet or bathing water, coughing, sneezing, or insect bites. The virus does not survive long outside the body, and mosquitoes do not inject blood from one person into another.

6Testing and treatment

You cannot tell whether someone has HIV by looking at them. Only a test can show it. Most tests detect antibodies against HIV, and some also detect parts of the virus itself. After infection there is a window period, from a few weeks up to about three months, when a test may still be negative, so a health worker may advise a second test.

Antiretroviral therapy (ART) is a combination of medicines taken every day for life. ART cannot cure HIV, but it stops the virus from multiplying. The amount of virus in the blood (the viral load) falls, often to a level too low to measure, and the CD4 count rises again. A person who takes ART every day, and whose viral load stays undetectable, does not pass HIV to sexual partners. Health workers summarise this as undetectable = untransmittable.

Worked example: reading CD4 counts

The table shows the CD4 counts of a man who did not know he had HIV, and so received no treatment.

1. Average fall per year: (900 − 180) ÷ 8 = 720 ÷ 8 = 90 cells per microlitre per year.
2. When did he develop AIDS? Between year 6 (350) and year 8 (180), when the count fell below 200.
3. Why did he feel well for years? In the latent stage the count was falling but still high enough to control most infections, so he had no symptoms. He could still pass HIV on.
4. What would testing have changed? If he had been tested early and started ART, the virus would have stopped multiplying, his CD4 count would have risen again, and he would not have developed AIDS.

Practice