CLICK TO VIEW :Sexual Practices Risk Chart | Routes of Transmission | Phases of HIV Infection.
In the worldwide epidemic, male-to-female and female-to-male transmission is the primary mode of HIV transmission. Experts estimate that 75% of the world's HIV infections have occurred through heterosexual transmission. Both semen and vaginal secretions contain HIV. Menstrual blood also contains HIV. The exact portal(s) of entry of the virus to the bloodstream is not clear. Several plausible explanations have been offered. One is that the HIV virus penetrates mucous membranes directly. Support for this hypothesis comes from research that has shown that uncircumcised males are more likely to be infected. These findings suggest that the foreskin holds infected fluids against the glans penis allowing an extended opportunity for the virus to penetrate. A second explanation is that the tissue-to-tissue friction associated with vaginal or anal intercourse produces lesions that allow points of entry for the virus. This belief is supported by data that show that anal intercourse with its higher probability of tissue damage is the most risky sexual practice. Further evidence for lesions to enhance transmission comes from epidemiologic studies that show that individuals with a history of genital ulcerative diseases (e.g. syphilis herpes chancroid) are more likely to be HIV infected.
Regardless of the exact mechanism of penetration of the virus, it is clear that contact with the sexual fluids of an HIV-infected person presents a risk of transmission of the virus. While it is impossible to quantify exactly the risk of transmission for various sexual practices there is evidence that some practices are more risky than others.
Phases of HIV Infection
Infection with HIV initiates a process of gradual and accelerating destruction of the body's immune system. The process can be described as having five phases. Transmission of the virus is possible during all five phases.
PHASE ONE: The first phase of the infection is an asymptomatic incubation period; which may be as short as 4 weeks or as long as 6 months. It is sometimes referred to as the window period. During this phase HIV replicates in the blood but the infected person exhibits no detectable physiological response. Also, during this phase the virus can be detected by laboratory tests used to detect the HIV antigen. These tests are rarely relied upon because they may elicit false negative results.
PHASE TWO: The second phase of the infection is a short symptomatic period early in the infection - called acute primary HIV infection. Infected people experience symptoms that are flu-like with fever, lymphodenopathy, skin rash, and malaise. A few people experience more acute symptoms: e.g., meningo-encephalitis with headache, stiff neck, high fever, convulsions, and alterations in consciousness and cognition. Although not all HIV-infected people remember experiencing symptoms, experts believe that the symptoms coincide with the body's production of sufficient detectable antibodies. Ideally, HIV-infected persons should be identified by antibody tests during this phase so that they can take precautions to prevent further transmission. Most individuals who are infected view these symptoms as signs of common influenza, however, and do not seek testing.
PHASE THREE: The third phase of infection is a prolonged asymptomatic period lasting from 1 year to as long as 15 to 20 years, depending on the state of the person's immune system at the time of infection and behaviours to maintain health and therapeutic interventions. The infected person continues to demonstrate serum antibodies against HIV. These antibodies, however, are not protective. During this period the infected person experiences a progressive decline in immune function associated with a fall in helper T-lymphocytes (CD4+ cells). However, because of the asymptomatic nature of this phase, few infected persons realize that they have been infected with HIV and have their immune status evaluated. Current anti-retroviral therapies have been shown to extend this phase. Therefore it is extremely important to identify HIV-infected persons during this asymptomatic period if they have not been diagnosed earlier. This third phase is called asymptomatic HIV infection.
PHASE FOUR: The fourth phase of HIV infection begins with the onset of symptoms of immune suppression in the infected person and continues until the person develops an AIDS-defining condition. This phase is sometimes referred to as persistent generalized lymphodenopathy. The symptoms result from two pathologic processes: (1) failure of the immune system to defend against pathogens and (2) the virus' direct attack on nerve cells. Symptoms vary, but may include persistent low-grade fever, night sweats, continuous or intermittent diarrhea, lymphodenopathy, unintended weight loss, oral lesions, fatigue, rashes, cognitive slowing, and peripheral neuropathy. Any of these symptoms are indicators that the disease is likely to progress to diagnosable AIDS within the next 2 to 3 years.
PHASE FIVE: The fifth phase of infection is AIDS. This means that the person has experienced immune suppression and acquired condition that meets the criteria for definition of an AIDS case as specified by the CDC (Centers for Disease Control). The criteria for defining an AIDS case were established to ensure uniformity in reporting of AIDS cases. Therefore, a diagnosis of AIDS should be considered an assist in determining the extent of HIV-related disease rather than a diagnosis for clinical management of infected persons. An AIDS diagnosis has important prognostic value as 80% - 90% of persons with a diagnosis of AIDS die within 3 years of the diagnosis. CDC expanded the criteria for the case definition to include all persons with a CD4+ T-lymphocyte count less than 200 cells/mm cubed. The expansion includes the addition of three new clinical conditions - pulmonary tuberculosis, recurrent pneumonia, and invasive cervical cancer - and retains the 23 clinical conditions in the AIDS surveillance case definition published in 1987. This new definition became effective January 1 1993 and is used throughout all states of America (and in Bermuda) for AIDS case reporting.