HIV infection spreads through four main routes: (a) sexual transmission, (b) blood transfusion, (c) injections, especially intravenous drug injections and (d) mother-to-child transmission during pregnancy or delivery. Figure 3 shows the probable source of HIV infections and AIDS in India. More than seventy-four per cent people are estimated to have got the infection through sexual transmission.

The effectiveness of transmission of the virus by various routes is not the same. Effectiveness of transmission means the chance or probability of getting the infection with one encounter with the virus through that route. The effectiveness is often expressed as percentage. This means the number of times a person can get HIV infection through exposures to the route of transmission. Box 1 shows the effectiveness of transmission by various routes. It is important to remember that although sexual route has a very low effectiveness of transmission, it accounts for more than seventy-four per cent infections in India. This is mainly because of the high frequency of occurrence of sex acts among people as compared to the frequency with which people take intravenous drugs or get blood transfusions.

HIV is present in all body fluids of an infected person. It is, however more in number in blood, semen and vaginal fluids. Semen is the thick whitish secretion of the male reproductive organs that is discharged from the same opening through which the urine comes out. Vaginal fluids are the secretions from the vagina, which is 38 a like a canal in the female reproductive system. It starts at the opening of the womb or uterus, and opens out of the body just behind the opening for urine and in front of the opening for stool. HIV virus can be easily killed by heat and by drying. Four main conditions must be fulfilled if HIV is to be transmitted through any one of the four routes mentioned above. These include:

  1. HIV must be present in the body fluids, especially the semen, vaginal fluids, blood.
  2. HIV must live during the period it is out of the body. It can live for a long time in blood stored at cold temperatures for transfusion but lives for a very short time in all other situations as the body fluids dry easily. HIV cannot survive in dried body fluids.
  3. There must be a convenient place for the virus to enter the body. The normal skin forms a very effective barrier against HIV and will find it difficult to enter the body through intact skin. The virus can easily enter the body from where there is either damage to the skin or the skin is more delicate (such as in vagina or the anus). Anus is the opening of the digestive tract through which stool is passed out of the body.
  4. The number of viruses in the body fluids must be adequate to infect others after it is transferred on contact with body fluids. If the number of viruses that enter another person is less, the infection may not occur.




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