AIDS stands for Acquired Immuno Deficiency Syndrome, first described in 1981. AIDS is the result of damage of the immune system. A damaged immune system is unable to protect the body against certain specific, ‘opportunistic’ infections and tumours. These are called opportunistic because they are caused by organisms which are normally controlled by the immune system but which take the opportunity to cause disease if the immune system has been damaged.
AIDS patients are sensitive to opportunistic infection by agents like viruses, bacteria, fungi and protozoans. AIDS victims also suffer a high frequency of some type of cancer especially lymphomas and Kaposis sarcoma.
AIDS is caused by a retrovirus (human immuno deficiency virus or HIV) was first described by Robert Gallo and Luc Montagnier in 1983.
HIV stands for Human Immuno Deficiency Virus. It belongs to a group of viruses, called retroviruses. Viruses copy their genetic material into the genetic material of human cells.
Through mechanisms which are not still fully understood, HIV prevents the immune system from working properly. Normally the body’s immune system would fight off infection. But HIV is able to infect cells (called CD4 cells) which coordinate the immune system’s fight against infection. Many are actually destroyed by being infected, others, including CD4 cells which are not themselves infected, no, longer work properly. HIV infects principally a specific type of lymphocytes, the T4 lymphocytes, which is required for a normal immune response.
Structure of HIV: HIV is an encapsulated circular virus having an average diameter of 90-120 nm (nanometer). In the centre of the capsule there is a single stranded RNA as genome and core proteins. The enzyme reverse transcriptase remains associated with the genomic RNA. With the help of this enzyme the RNA replicated and transformed into DNA genome (single stranded) and then into double stranded DNA. This stage is called provirus. Provirus may remain in an inactive form for a long time. RNA is synthesized from the provirus with the activity of viral promoter gene. The core of the virus remains covered with nuceo-caspid shell. When the naked virus comes in contact with the outer covering of the host cell membrane bilayered lipoprotein membrane is developed. This lipoprotein is synthesized from the lipid layer of the host cell but the glycoprotein is made by the viral gene codes. A portion of this protein is spike cell. The extended portion is called pedicles. The spikes make the infrastructure of the virus and binds with the CD-4 receptor of the host.
Stages of HIV infection:
Cell tropism: The receptor antigen of viral spike protein is CD4. So the virus can attack and infest those cells having CD4. T-4 is commonly infected by the virus due to presence of CD4 in T-lymphocytes. B-lymphocytes possess 5-10 %, Monocyte 10-20 % CD4, therefore, they are also attacked by the virus.
Pathogenesis: HIV enters into the blood or any tissue and attacks the T-4 lymphocytes. The pathogen can enter through blood transfusion and sexual mating. After enter into the host nucleus the viral genome may remain in a dormant state for a number of years or infect the cell. HIV usually destroys the T-4 cells. The infected T-4, then cannot secretes interleukin 2 gamma interferon or other lymphokines. As a result, the cells losses their immunity.
AIDS infected patients do not give responses to any other antigen. On the other hand, hypergamma globulineaemia can be developed due to polyclonal activation of B-lymphocyte. This increases the rate of IgG and IhA level. In this way the HIV destroys the humoral sanctity. Since T-lymphocyte cannot secrete the active secretory substances. So, the macrophage cannot destroy antigen anymore. Therefore, the immune response is totally destroyed.
Stages of HIV infection:
Becoming HIV antibody positive: Most people who become infected with HIV do not immediately notice that they have been infected. Some have a short illness soon after they become infected. This is called ‘seroconservation illness’, because it coincides with the time that blood testes for HIV antibodies will become positive. The illness may take the form of sore throat, a fever or a rash, or rarely more severe illness.
Asymptomatic HIV infection: Initially any damage caused by HIV has not outward effect. This is called asymptomatic infection, which may last for many months or years. Sometimes, people with asymptomatic HIV infection may have swollen lymph nodes, which is called PGL (persistent generalized lymphadenopathy).
Symptomatic HIV infection: Statistical studies of people with HIV have shown that more time passes, the, more likely it is than the damage will become more severe and opportunistic infections or tumors may develop.
HIV can also have direct effects upon the body. For instance, the virus can also attack immune cells in the brain. In such case, the brain or nervous system may not work properly. This is called HIV associated dementia. If people become ill because of these infections or tumours, they are said to have symptomatic HIV infection.
The last stage of HIV infection is the development of AIDS. AIDS completely destroys the immune system of the infected person. This may lead to various diseases. AIDS damage the following systems of man.
(i) Respiratory system: AIDS patients suffer from dry cough, and fever. The patients may be secondarily infected by tuberculosis bacteria.
(ii) Gastro-intestinal disorders: AIDS patients suffer from various types of gastro-intestinal problems.
(iii) Central nervous system: AIDS infected patients may be infected by toxoplasmosis, cryptococcosis. Patients may develop cerebral lymphonoma.
(iv) Malignancies: AIDS patients may become the victim of many types of cancers.
(v) Dementia: HIV may destroy the brain cells, thereby, leading to dementia.
(vi) Infection among newborn: HIV infected mother usually produce HIV infected babies. Among the born babies, 50 % gets infected and usually dies within one year. Children may get the HIV from the transfusion of blood.