HIV Infection and AIDS
The human immunodeficiency virus (HIV) causes acquired immunodeficiency syndrome (AIDS), a disease that without treatment ultimately kills most of its victims. On average, with the best treatment currently available, someone with HIV infection will live 20 to 30 years or more after diagnosis. For most people infected with HIV worldwide, however, adequate treatment is not available, and most infected persons die within 10 years.
An estimated total of 65 million people have been infected since the epidemic began in 1981 nearly 1% of the world’s population and tens of millions of those people have died. Currently, about 34 million people are infected with HIV/ AIDS worldwide.
Worldwide, the number of people living with HIV infection has leveled off. Many experts believe that the global HIV epidemic peaked in the late 1990s, at about 3.5 million new infections per year, compared with an estimated 2.5 million new infections in 2011. Despite a slowing of the epidemic, however, AIDS remains a primary cause of death in Africa and continues to be a major cause of mortality around the world.
In the United States, nearly 1.7 million people are living with HIV infection; about 51,000 new HIV infections
STIs are caused by more than 30 different organisms, including viruses, bacteria, fungi, and protozoa.
HIV Infection and AIDS Photo Gallery
Does Exercise Help or Harm the Immune System?
Like any infectious illness, STIs attract the attention of the body’s immune system an information network operating through billions of specialized white blood cells to protect the body from disease. When an infection is detected inside the body, these cellular defenders including lymphocytes, macrophages (“big eaters”), and “natural killer” cells, among others spring into action. They attack invading pathogens, destroy body cells that are already infected, and prime the immune system in case of future infections by the same agent. This is even the case in HIV infection. Although HIV targets specific types of immune system cells primarily CD4 T cells and other kinds of T cells other immune cells pick up the fight and attempt to rid the body of the virus.
A strong immune system can help defend your body against infections, including STIs, if only by keeping the infection at bay and minimizing damage until medical therapy (such as antibiotics) can be started. Many lifestyle factors, including nutrition, sleep, and stress management, are known to support immune function. The effects of physical activity and exercise on the immune system are more complex. It appears that effects vary depending on the intensity of the activity. Research has demonstrated that moderate-intensity exercise tends to improve immune function, whereas vigorous-intensity exercise tends to impair immunity temporarily.
A 2013 study found that patients with HIV/AIDS could exercise at low to moderate intensity and not increase their risk for developing other infections. Aerobic exercise and resistance training improved muscle and cardiovascular endurance and also prevented muscle wasting due to HIV. Resistance training has also been shown to improve strength in frail older adults with HIV. It is possible that strength training increases CD4 cell counts. Other studies have examined the effects of exercise on specific components of the immune system (such as natural killer cells, neutrophils, and dendritic cells) and found that the overall immune system response to physical activity is positive.
Intensive training for long periods has mixed short and longterm effects. On one hand, studies have found that people who exercise vigorously, for prolonged periods, or without proper nutrition experience temporary declines in immune system function; full function is then typically recovered in a matter of hours or days. But longitudinal studies (those conducted repeatedly over longer periods of time, such as months or years) also show that vigorous exercise offers important anti-inflammatory benefits. For most of us, the evidence strongly indicates that regular moderate-intensity exercise promotes immune system function in many ways.
What Is HIV Infection? HIV infection is a chronic disease that progressively damages the body’s immune system, making an otherwise healthy person less able to resist a variety of infections and disorders. Normally, when a virus or other pathogen enters the body, it is targeted and destroyed by the immune system. But HIV attacks the immune system itself, taking over immune system cells and forcing them to produce new copies of HIV. It also makes them incapable of performing their immune functions (see the box “Does Exercise Help or Harm the Immune System?”).
The destruction of the immune system is signaled by the loss of CD4 T cells. As the number of CD4 T cells declines, an infected person may begin to experience mild to moderately severe symptoms. A person is diagnosed with AIDS when he or she develops one of the conditions defined as a marker for AIDS or when the number of CD4 T cells in the blood drops below a certain level (200/p1). People with AIDS are vulnerable to a number of serious often fatal secondary, or opportunistic, infections.
CD4 T cell A type of white blood cell that helps coordinate the activity of the immune system; the primary target for HIV infection. A decrease in the number of these cells correlates with the risk and severity of HIV-related illness.
The asymptomatic or incubation period of HIV the time between the initial viral infection and the onset of disease symptoms may range from 2 to 20 years, with an average of 11 years in untreated adults. Most, but not all, infected people experience flulike symptoms shortly after the initial infection, but most remain generally healthy for years. During this time, however, the virus is progressively infecting and destroying the cells of the immune system. People infected with HIV can pass the virus to others even if they have no symptoms and especially if they do not know they have been infected.
Transmitting the Virus HIV lives only within cells and body fluids, not outside the body. It is transmitted by blood and blood products, semen, vaginal and cervical secretions, and breast milk. It cannot live in air, in water, or on objects or surfaces such as toilet seats, eating utensils, or telephones. A person is not at risk of getting HIV infection by being in the same classroom, dining room, or even household with someone who is infected.
There are three main routes of HIV transmission:
• Specific kinds of sexual contact
• Direct exposure to infected blood
• Contact between an HIV-infected woman and her child during pregnancy, childbirth, or breastfeeding
These means of transmission are discussed in the following sections.
SEXUAL CONTACT HIV is more likely to be transmitted through unprotected vaginal or anal intercourse than by other sexual activities. During vaginal intercourse, male-to-female transmission is more likely to occur than female-to-male transmission. HIV has been found in preejaculatory fluid, so transmission can also occur before ejaculation. Any trauma or irritation of tissues, such as those that can occur through rough or unwanted intercourse or through the overuse of spermicides, increases the risk of HIV transmission. The presence of lesions or blisters from other STIs also makes it easier for the virus to be passed.
Oral-genital contact carries some risk of transmission, although less than vaginal or anal intercourse. The risk of HIV transmission during oral sex increases if a participant has oral sores, even if from poor oral hygiene practice (which can include bleeding gums from vigorous flossing or brushing just before or after oral sex). Some evidence suggests that drinking alcohol before oral sex may make the cells that line the mouth more susceptible to infection with HIV.
Among Americans with AIDS, the most common means of HIV exposure is sexual activity between men (MSM); heterosexual contact and injection drug use (IDU) are the next most common (Figure 14.1). Direct contact with infected blood is another major route of HIV transmission.