By Barry C. Fox, M.D., University of Wisconsin
More than three decades after the first cases of AIDS, were reported, the world is still dealing with a pandemic of 33 million people currently infected with the HIV virus, of which around 3 million are children. There is still no cure, and we have lost nearly 25 million people to the disease. But how does an HIV infection lead to AIDS?
World HIV Infections
HIV is the number one cause of death in Africa, and the leading single cause of death from an infectious disease all over the world. Even though the numbers of deaths have declined—partly due to new treatments and prevention—there are more than 6000 new infections daily worldwide. You may be surprised to know that most of the new cases are transmitted heterosexually, although many people in the United States think of HIV as a disease of gay males. In fact, over half of the HIV victims worldwide are women.
Even in the U.S., there are over a million people living with HIV. These are just the reported cases. The incidence of HIV infection in the U.S. over the past decade has decreased by 33 percent. But one very disturbing fact is that 1/4 of the new cases of HIV in the U.S. are between the ages of 13 and 24, and the majority are unaware that they are infected.
This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now, on Wondrium.
The Sources of HIV Infection
These figures have major implications for America’s youth. Unfortunately, only 22 percent of high school students who are sexually active have ever been tested for HIV. Persons are infected by sharing body fluids, including blood, seminal and vaginal fluids, and even breast milk.
If the fluids containing HIV virus come into contact with damaged mucous membranes or the skin, the virus can enter into the surface cells, and then, over the course of the next several days, make its way into the bloodstream and spread. HIV can also be transmitted by needles, by intravenous drug use as shared needles result in direct inoculation of the blood.
Learn more about how viruses hijack your body cells.
When HIV was first discovered, people were very wary about socializing with those infected with the virus. They didn’t understand how it was even transmitted. But HIV is not spread by hugging, or by shaking hands, or by sharing dishes or glasses, or by toilet seats.
Although it seems logical that HIV could possibly be spread through saliva, the saliva of infected individuals contains only noninfectious components of HIV. Saliva has immune defense properties that disrupt cells that are the actual carriers of the virus. Importantly, HIV cannot be transmitted through the air, and it doesn’t survive long outside the body.
The only mandatory testing for HIV in place at this time is for blood and organ donors, military personnel, some inmates, and occasionally in newborns in some states. The CDC does recommend routine HIV screening in primary care settings for all adults of ages 13 to 64, at least once in your lifetime, and repeat screening at least annually for those at high risk.
HIV at Birth
HIV can be transmitted from mother to child during pregnancy, birth, or even breastfeeding. Accordingly, the CDC recommends routine testing as part of prenatal care.
HIV is a lentivirus, a family of viruses which typically has a long incubation period before it causes clinical illness. It is also classified as a retrovirus. Once individuals are infected, similar to herpes viruses, they are infected for life. The human immune system can’t seem to make the virus disappear, paradoxically because the virus is actually attacking the portion of the immune system that is normally responsible for immune clearance.
CD4 Cell Attacks
We know that HIV can hibernate for extended periods of time in the body, but especially in the lymph nodes, bone marrow, and spleen, areas of importance to our immune system. The main cells that HIV attacks are of the immune system, and they’re known as the CD4 cells. T-helper cells, as its name implies, assists with a larger number of important immune responses of the body. With reduced T-helper CD4 cells, the immune system is handicapped, and may eventually be crippled.
The HIV virus has the ability to destroy more than a billion CD4 cells daily. HIV replication occurs directly in these cells. After the initial infection, the body’s production of CD4 cells can compensate for the losses. But, over time, as the HIV destruction process continues, the immune system gradually declines with reduced numbers of CD4 cells.
What is AIDS?
We know that HIV is the virus that causes AIDS. But what exactly is AIDS? AIDS isn’t really a disease; it’s a complicated syndrome with many symptoms. AIDS is the last stage of an HIV infection. The immune system is so damaged that people begin to get opportunistic infections, meaning they normally would not occur with healthy immune systems. Typically, the normal number of CD4 cells in our body is greater than 500 cells per milliliter of blood.
When the cell count falls to under 200 per milliliter, infections are likely to appear in a human body. Examples of such infections include pneumocystis pneumonia and cryptococcal fungal meningitis. Cancers are also much more common in AIDS, including lymphomas, and a particularly virulent skin cancer known as Kaposi’s sarcoma.
Learn more about our immune system.
Fortunately, in developed countries with anti-retroviral drugs, most patients no longer get to this stage of their illness. With proper treatment, called anti-retroviral therapy or ART, patients can usually keep the level of HIV virus low. ART is the use of HIV medications to fight HIV infection. It involves taking a combination, or cocktail, of HIV medications every day.
These medications control the virus so that patients can live a longer, healthier life. ART also reduces the risk of HIV being transmitted to others. Today, people in developed countries who are treated before the disease becomes advanced and have their illness under control can have a nearly normal life expectancy.
Common Questions about HIV Transmission and AIDS
Persons are infected by HIV by sharing body fluids, including blood, seminal and vaginal fluids, and even breast milk. The virus can enter into the surface cells, and then make its way into the bloodstream and spread.
HIV is a lentivirus with a long incubation period before it causes illness. It is also classified as a retrovirus. Once individuals are infected, similar to herpes viruses, they are infected for life.
AIDS isn’t really a disease; it’s a syndrome. AIDS is the last stage of an HIV infection. The immune system is so damaged that people begin to get opportunistic infections.