HIV1 Spreads by Sexual Contact Infected Blood and from Mother to Infant

Although the precise mechanism by which HIV-1 infects an individual is not known, epidemiological data indicate that common means of transmission include homosexual and heterosexual intercourse, receipt of infected blood or blood products, and passage from mothers to infants. Before tests for HIV in the blood supply were routinely used, patients who received blood transfusions and hemophiliacs who received blood products were at risk for HIV-1 infection. Exposure to infected blood accounts for the high incidence of AIDS among intravenous drug users who normally share hypodermic needles. Infants born to mothers who are infected with HIV-1 are at high risk of infection. Unless infected mothers are treated with anti-viral agents before delivery, approximately

GLOBAL TOTALS

• People living with HIV/AIDS, December 2000: 36.1 million > New infections in 2000: 5.3 million

Cumulative: 21.8 million

GLOBAL TOTALS

• People living with HIV/AIDS, December 2000: 36.1 million > New infections in 2000: 5.3 million

Cumulative: 21.8 million

Distribution Aids

FIGURE 19-7

The global AIDS epidemic. The estimated worldwide distribution of AIDS cases as of December 2000. There were approximately 36.1 million persons living with AIDS as of December 2000; most of these were in sub-Saharan Africa and Southeast Asia. In

North America and Western Europe, about 80% of those affected were men, whereas in Africa nearly equal numbers of women and men have AIDS. [HIV/AIDS UNAIDS: Report on the Global Epidemic, 2000.]

Australia/New Zealand ' 15,000

Vj v

FIGURE 19-7

The global AIDS epidemic. The estimated worldwide distribution of AIDS cases as of December 2000. There were approximately 36.1 million persons living with AIDS as of December 2000; most of these were in sub-Saharan Africa and Southeast Asia. In

North America and Western Europe, about 80% of those affected were men, whereas in Africa nearly equal numbers of women and men have AIDS. [HIV/AIDS UNAIDS: Report on the Global Epidemic, 2000.]

30% of infants born to them will become infected with the virus (see Clinical Focus). Possible vehicles of passage from mother to infant include blood transferred in the birth process and milk in the nursing period. Transmission from an infected to an uninfected individual is most likely by transmission of HIV-infected cells—in particular, macrophages, dendritic cells, and lymphocytes.

In the worldwide epidemic, it is estimated that 75% of the cases of HIV transmission are attributable to heterosexual contact. While the probability of transmission by vaginal intercourse is lower than by other means, such as IV drug use or receptive anal intercourse, the likelihood of infection is greatly enhanced by the presence of other sexually transmitted diseases (STDs). In populations where prostitution is rampant, STDs flourish and provide a powerful cofactor for the heterosexual transmission of HIV-1. Reasons for this increased infection rate include the lesions and open sores present in many STDs, which favor the transfer of HIV-infected blood during intercourse.

While the AIDS epidemic has engendered an understandable fear of infection among most informed individuals, there are also exaggerated claims of the ease with which HIV infection may be passed on. At present, there is no evidence that casual contact with or touching an infected person can spread HIV-1 infection. Airborne transmission has never been observed to cause infection. In virtually every well-documented case of HIV-1 infection, there is evidence for contact with blood, milk, semen, or vaginal fluid from an infected individual. Research workers and medical professionals who take reasonable precautions have a very low incidence of AIDS, despite repeated contact with infected materials. The risk of transmitting HIV infection can be minimized by simple precautionary measures, including the avoidance of any practice that could allow exposure of broken or abraded skin or any mucosal membrane to blood from a potentially infected person. The use of condoms when having sex with individuals of unknown infection status is highly recommended. One factor contributing to the spread of HIV is the long period after infection during which no clinical signs may appear but during which the infected individual may infect others. Thus, universal use of precautionary measures is important whenever and wherever infection status is uncertain.

It is a sobering thought that the epidemic of AIDS came at a time when many believed that infectious diseases no longer posed a serious threat to people in the United States and other industrialized nations. Vaccines and antibiotics controlled most serious infectious agents. The eradication of smallpox in the world had recently been celebrated, and polio was yielding to widespread vaccination efforts; these were considered milestones on the road to elimination of most infectious diseases. The outbreak of AIDS shattered this complacency and triggered a massive effort to combat this disease. In addition, the immunodeficiency that characterizes AIDS has allowed re-emergence of other infectious diseases, such as tuberculo sis, which have the potential to spread into populations not infected with HIV.

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