A person infected with HIV is not likely to have any symptoms for about three to ten years. This period may be longer if the natural defence mechanism of the body is good. As mentioned earlier, although a person infected with HIV does not have any symptoms, he/ she can spread the infection to others. This is why it is recommended that anyone who has sex with a partner who is not in mutually faithful relationship should practice safe sex. This means using a condom correctly for every sexual act.

In order to understand why HIV infection does not cause symptoms for a long time, it is important to understand the events that take place in the body soon after HIV enters it. As mentioned earlier, HIV infects a large number of CD4 cells soon after it enters the body. It multiplies rapidly in the T4 cells that contain CD4 particles. During the early or acute stage of the infection, the blood will contain a large number of viral particles. These particles rapidly spread through various organs and infect several organs of the body. They particularly infect the organs of the lymphatic system.

Lymphatic system is a vast, complex network of capillaries, thin vessels, ducts, valves and organs. This entire network helps to protect and maintain the internal fluids of the body. They do this by producing, filtering and transporting lymph to various parts of the body. Lymph is a thin clear fluid that is produced by various organs of the body and is circulated in the lymphatic network. It enters the bloodstream in the large veins of the neck.

There are small nodes called lymph nodes in the lymphatic system. They filter the lymph and fight infection. Various types of blood cells essential for fighting infection are formed in the lymph nodes.

The effect of HIV infection on the lymphatic system results in decrease in the total number of CD4 and T cells in the bloodstream by twenty to forty per cent. Two to four weeks after the first entry of the virus in the body, up to seventy per cent people suffer flu-like symptoms related to acute infection. The symptoms may be fever, headache, enlarged lymph nodes and a general feeling of being unwell. All these symptoms are often mild and not very specific. This is why it is difficult to differentiate symptoms due to HIV infection from those of other viral infections. By the time the flu-like symptoms appear, the normal defence mechanism of the body fights back with the killer T cells and the antibodies produced by В cells. As a result, the HIV levels in the body reduce dramatically and the total number of CD4 and T cells may go back to eighty to ninety per cent of the original levels.

After the active stage of multiplication and the body's response to the virus, a person infected with HIV will not have any symptoms for several years. During this time, the HIV continues to multiply in the organs of the lymphatic system. Most scientists believe that this is because after the initial activity of the T cells where they kill the HIV, they seem to exhaust themselves and disappear. In the absence of the killer cells, HIV continues to multiply. Also, the killer T cells tend to accumulate in the blood whereas the HIV is largely located in the lymphatic system.

People with HIV infection do not develop persistent severe symptoms for up to ten years after the virus first enters the body. Children born with HIV infection may however develop the symptoms within two years. The symptoms appear because of the gradually diminishing defence mechanism of the body. This is the stage when AIDS develops. Most symptoms of AIDS are due to opportunistic infections that take advantage of the body's poor defence mechanism. Opportunistic infections are those infections that may not cause disease in a person with normal defence mechanism.

The symptoms of AIDS are divided into major and minor symptoms. As per the definition of AIDS given by the World Health Organisation, a person is said to have AIDS if he/she has at least two major signs and at least one minor sign and there is no other cause of poor immune mechanism. The term "AIDS related illness" is used when a person has some of the signs and symptoms, has antibodies to HIV in the blood but does not have two major and one minor sign.