What Does HIV Do in the Body?

AIDS is the most severe form of disease caused by HIV (human immunodeficiency virus), a virus that damages the immune system, leaving a person open to many life-threatening infections.

How Did the AIDS Epidemic Begin?

In the early 1980s, doctors in New York and California began noticing a very unusual disease in a small number of young men. The men, who were mostly homosexual, were developing unusual infections and cancers, and some of them were dying. The infections were similar to those seen in children who are born with very weak immune systems. But these men had been healthy as children and should have had normal immune systems.

Government scientists searched for other cases of the disease, and found more and more of them. The disease also seemed to strike people who had received blood transfusions, and drug addicts who had shared needles with each other. Reports of the disease began to come in from other countries, including African and Caribbean countries, where it seemed to spread mainly by sexual contact between men and women. Some babies were born with it, too.

AIDS

Less than 20 years later, that mysterious disease had become one of the worst epidemics ever to strike humanity. AIDS (acquired immune deficiency syndrome) had killed almost 14 million people worldwide, including more than 3 million children, by the end of 1998. In the United States, AIDS had killed more than 400,000 people, including almost 5,000 children younger than age 15.

HIV

Even greater numbers of people are infected with the virus that causes AIDS, but have not yet developed the disease. In the United States, almost a million people are thought to be infected with HIV, the human immunodeficiency virus, and most do not know they are carrying the virus that causes AIDS. Within 10 years of becoming infected, about half of them will have developed AIDS. Worldwide, more than 33 million people are living with HIV infection, mostly in developing countries in Africa and Asia.

People at risk

Like other sexually transmitted diseases, HIV infection is a particular risk among teenagers and young adults. In the United States, more than 110,000 people in their twenties have been diagnosed with AIDS, and it is likely that most of them became infected with HIV when they were teenagers. It is estimated that up to one quarter of all HIV infections in the United States—and half of all HIV infections worldwide—occur in teenagers and people in their early twenties.

Many billions of dollars have been spent to understand HIV/AIDS, to prevent it, and to treat it. Although there is still no cure and no proven vaccine, there has been progress. Because of new drugs, the number of deaths from AIDS fell sharply in the United States starting in 1996. Many Americans infected with HIV are living longer and better lives: they are going to school, working, raising their families, and enjoying life. There is hope that in the United States, HIV will soon be similar to other chronic^* diseases, like diabetes or asthma: a serious disease, but one that is manageable with good medical care.

.How Does HIV Spread?

HIV infection can spread only when an infected person's body fluid (blood, semen, vaginal fluid, breast milk, or any body fluid containing blood) enters the bloodstream or contacts the mucous membrane^* of another person.

Sexual intercourse, either homosexual (between men) or heterosexual (between men and women), is responsible for most cases of HIV infection. The virus also commonly spreads among people who share contaminated needles when they inject drugs. Infected mothers may pass it on to their babies during pregnancy, childbirth, or breast-feeding.

If blood is infected, transfusions can spread HIV. But in the United States, blood transfusions have been tested for HIV since 1985, and the risk of infection from a transfusion is extremely low.

Oral sex also can spread the virus, and at least one case has been reported in which the virus is thought to have spread through wet kissing (French kissing).

^*mucous membrane is the kind of tissue that lines body openings, such as the mouth, vagina, and rectum, as well as the respiratory, intestinal, and genital tracts.

HIV does not spread through air, water, food, or objects like doorknobs or toilet seats. It is not spread by mosquitoes or by other insects. A person cannot "catch HIV" by playing with, going to school with, shaking hands with, hugging, or even living with an infected person. Fortunately, HIV is much less contagious than many other infections, including chickenpox, flu, or hepatitis B.

How Can HIV Infection Be Prevented?

Prevention of HIV infection is easy—and hard. People can completely protect themselves by never sharing needles, whether for drug use or such practices as tattooing or body piercing, and by avoiding all sexual contact. As people grow up and become sexually active, however, things become more difficult.

Safer sex

The safest sexual relationship is between two uninfected people who have sex only with each other, sometimes called a monogamous (mo-NA-ga-mus), mutually faithful relationship. But there is no sure way to tell if a person is infected or not. People with HIV may seem completely healthy and often do not know they are infected. In the first few months after infection, they may even test negative on HIV tests.

So if people are sexually active, how can they reduce their chances of infection? One important step is not to have sexual contact with anyone who may be at risk of HIV infection. Who is at risk? Anyone who ever shared needles or engaged in promiscuous sex (had many sexual partners), as well as anyone who ever had a sexual partner who shared needles or engaged in promiscuous sex. Of course, often people are not truthful about past behavior. To judge whether a potential sexual partner is being honest, or is at risk, it may help to know the person well, over a long period of time. Unfortunately, however, that, too, is no guarantee.

Other safety measures

Other steps to reduce the chances of infection include:

• using latex condoms correctly and consistently during sexual activity
• not engaging in anal sex or other sexual practices likely to cause breaks in the skin
• not having sexual relations with multiple sexual partners
• avoiding drugs and alcohol, since their use might prevent people from making good decisions about protecting themselves and others from HIV
• getting prompt treatment for any sore or blister in the genital area, since these can act as an open door for HIV to enter the body.

. What Does HIV Do in the Body?

Once HIV gets into the body, it attacks and enters white blood cells called CD4 helper lymphocytes (LIM-fo-sites). These cells are very important for the proper functioning of the immune system. When the virus begins to destroy CD4 cells more rapidly than the body can replace them, the immune system becomes so weak that severe infections and cancers can develop. The virus also can directly attack some organs, including the brain, the kidneys, and the heart.

The retrovirus HIV invades a body cell called a CD4 helper lymphocyte. Once inside the lymphocyte, HIV combines its genetic material with the CD4 cell's genetic material. After that, whenever the CD4 cell reproduces itself, it also reproduces HIV. HIV can destroy CD4 lymphocytes and spread throughout the body during active AIDS infections.

HIV is a special kind of virus called a retrovirus (see sidebar) and includes two species, or types. HIV-1, which is far more common and more severe, has caused the current epidemic. Different subtypes of it occur in different parts of the world. HIV-2, which is seen in some parts of West Africa, causes a milder version of AIDS.

One reason it has been impossible so far to find an HIV cure or vaccine is that the virus can mutate and change its genetic features with amazing speed. That means HIV can quickly grow resistant to a medicine, making the drug no longer effective. It also means that any drug or vaccine must be able to work against a wide range of different strains of HIV.

What Are the Symptoms?

HIV Infection

Between two and four weeks after people get infected, most people develop a flu-like illness with fever, sore throat, muscle aches, and (often) a rash that looks a little like measles. After two weeks, this illness usually disappears. Others, however, get infected with no initial symptoms of illness. A person can transmit HIV to others without having had any symptoms.

Over the next few years, a person may suffer fevers, swollen glands, fatigue, weight loss, and diarrhea. These symptoms generally occur long before the serious complications that come with AIDS. Some people may have minor infections such as thrush (a yeast infection of the mouth) or shingles (a skin infection caused by the virus that causes chickenpox). Others do not have any symptoms until they develop AIDS itself.

Children, especially those who were infected before they were born, generally develop symptoms more quickly than adults. Often they are sick from birth or may fail to grow and develop at a normal rate.

How Is HIV/AIDS Diagnosed?

Doctors may suspect HIV infection from the symptoms, especially if a person has one of the rare infections mentioned above. But HIV infection can only be diagnosed by blood tests.

Testing for HIV

Doctors recommend testing for all people who think they may have been exposed. Testing is also recommended for all pregnant women and for newborns whose mothers either tested positive for HIV or were not tested during pregnancy. Such testing should lead to treatment that cuts the baby's risk of getting HIV from the mother. Treating an infected woman with the drug AZT (zidovudine) during pregnancy and delivery, and treating her newborn with the same drug after birth, reduces the baby's risk of getting HIV from about 25 percent to about 6 percent.

The most common HIV test detects antibodies, which are substances the body makes to fight the virus. This test may not show infection until several months after it has occurred. For that reason, a person who was recently infected may test negative. So people who think they may have been exposed to the virus should be tested immediately and again six months later.

WHERE DID HIV COME FROM?

Since the identification of AIDS in 1981, and the discovery of HIV (the human immunodeficiency virus that causes AIDS) in 1983, scientists have tried to discover the origin of the virus. They came to suspect that it had developed in Africa from a monkey virus known as SIV (simian immunodeficiency virus) and that it might have spread to humans from chimpanzees.

But it was not until 1999 that an international team of researchers found what could be the missing link: a virus that seems to be a genetic blend of HIV and SIV. It was found in one subspecies of chimpanzee, Pan troglodytes troglodytes, but it seems to cause them no illness. Researchers suspect that humans first became infected with SIV about 50 years ago when they were exposed to the chimps' blood while hunting the animals for food. Once in humans, it appears, the virus changed into the deadlier HIV we know today.

Researchers were elated at the discovery of the microbe they called SIVcpz (cpz stands for chimpanzee). Because it does not make infected chimps sick, studying what it does in their bodies may help scientists learn how to prevent HIV from making people sick. And it may help them prevent the spread of other viruses to humans in the future.

But the scientists got a harsh surprise. The type of chimp involved, they learned, soon may be extinct in the wild. Logging is driving the animals out of their rainforest homes in West and Central Africa, and they are being butchered as game meat. Now scientists are trying to save the chimps, as well as study them.

"We cannot afford to lose these animals," said Dr. Beatrice Hahn of the University of Alabama, one of the lead researchers involved. "Chimpanzees may represent both cause and solution to the AIDS problem."

What Is a Retrovirus?

One reason HIV is so dangerous is that it is a special kind of virus—a retrovirus. This means that it reproduces itself in a backward or "retro" manner. To understand what that means, it helps to know some basic information about viruses.

Viruses are tiny microbes—much smaller than bacteria—that are made largely of nucleic acid, the substance that makes up genes. They work by invading a cell and using the cell's energy and machinery to make copies of themselves.

The virus's nucleic acid may be either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid). DNA viruses make direct copies of their DNA, and most RNA viruses make copies of their RNA. This copying process is called transcription. Retroviruses contain RNA but copy it into DNA in a process called reverse transcription. Then the viral DNA—called a provirus—is inserted directly into the genetic core of the cell. That means that wheneverthe cell reproduces itself, by making copies of its own DNA, it also makes copies of the retrovirus's DNA.

In the case of HIV, the virus invades CD4 helper lymphocytes, which are white blood cells important to the immune system.

In addition, for the first year or so of life, a baby born to an infected mother may test positive for HIV even if the baby is not infected.

Testing for CD4 lymphocytes

Once a person is known to be infected, a different blood test is done periodically to see how well the person's immune system is working. The test measures the level of CD4 lymphocytes, the type of white blood cell targeted by HIV. If the number of these cells falls below a certain level—or if the person has certain severe infections like those described earlier—then the person is said to have AIDS.

How Is HIV/AIDS Treated?

Drugs to fight the virus directly are generally prescribed as soon after infection as possible. These drugs block protease and reverse transcriptase, which are important enzymes^* that the virus makes in order to reproduce itself. The drugs are used in combinations of three to five medications, which is a form of treatment called HAART (highly active antiretroviral therapy).

The most powerful of these drugs are also the newest, so no one knows how effective they may be in the long run. But it is clear that they postpone the development of AIDS and often make other symptoms less frequent and less severe. Unfortunately, HIV may become resistant to one or more of the drugs. In addition, all the anti-HIV drugs have side effects that make them difficult for many patients to take. It is not yet known whether these drugs reduce the chance that an infected person will pass HIV to someone else.

Besides the antiviral drugs that attack HIV directly, other medications can help prevent or treat some of the serious infections that come with AIDS.

Histoplasmosis and HIV

In some areas of the United States, especially southern and southwestern areas, almost 80 percent of the population tests positive for the fungal infection histoplasmosis (his-to-plaz-MO-sis).

In the past, only people with severe cases of histoplasmosis required treatment, but HIV and AIDS have caused an increase in those numbers.

People with HIV, AIDS, and other immune system diseases should avoid activities that increase their chance of exposure to histoplasmosis. Such activities include cleaning chicken coops, disturbing soil beneath bird-roosting sites, and exploring caves. Once infected, people with histoplasmosis and HIV require ongoing treatment.

Bob drives a cab. When he gets busy at work, it is hard for him to remember to take the pills at just the right time and to be sure he has water with him. Plus, the nelfinavir gives him diarrhea. He has also noticed that he is beginning to develop a large pot belly. His doctor warned him that the nelfinavir might cause this.

Some days he feels encouraged thinking how the drugs are helping him. Other days he gets so depressed about all the pills and the side effects that he feels like giving up. But for now, he has decided to do what the doctor said and try never to miss a single dose. He just hopes he can keep hanging on and that better medicines come out soon.

Living with HIV/AIDS

In the early days of the epidemic, parents picketed outside schools to keep HIV-infected children out, and workers feared sitting next to someone with AIDS. Today, most Americans realize that HIV cannot be caught just by being around someone who has it. But people infected with HIV still can face stigma and discrimination. For many people, telling family and friends they are infected also means revealing something they have been keeping secret about themselves—that they are gay, or that they have used illegal drugs, or that they have had sex with many people. This can be very difficult, especially for young people who are gay and may fear rejection by their families. Often, however, people with HIV find that family and friends are very supportive.

To help stay healthy with HIV, good health habits become even more important. These include:

• for everyone: eating ample amounts of nutritious food, exercising, and getting adequate rest
• for drug addicts: stopping drug use
• for smokers: quitting smoking
• for people who have no symptoms: getting regular checkups, preferably by doctors who have a lot of experience treating HIV/AIDS
• for people who are taking medications: taking them properly and consistently, because taking these medicines on and off can cause a person's virus to become resistant to them.

Many people with HIV live normal lives for many years. Even those who struggle with bouts of illness often carry on with great fortitude and continue to enjoy their lives, just like people with any other chronic, life-threatening illness