AIDS and cancer
Causes, spread and prevention of AIDS; nature and causes of cancer.
The essentials
AIDS (Acquired Immuno Deficiency Syndrome) is a deficiency of the immune system acquired during a person's lifetime. It was first reported in 1981. It is caused by the Human Immunodeficiency Virus (HIV), a retrovirus with an RNA genome. Transmission occurs by sexual contact with an infected person, transfusion of contaminated blood, sharing infected needles (as in intravenous drug users) and from an infected mother to her child through the placenta. HIV does not spread by mere touch or physical contact.
After entering the body, the virus enters macrophages, where its RNA is copied to viral DNA by reverse transcriptase. Viral DNA is incorporated into host DNA and directs production of viruses; macrophages act like an HIV factory. HIV then enters helper T-lymphocytes (TH), replicates and destroys them, so their number decreases progressively. The person then suffers from infections by bacteria (especially Mycobacterium), viruses, fungi and parasites like Toxoplasma. A widely used diagnostic test is ELISA. Anti-retroviral drugs are only partially effective; they can prolong life but cannot prevent death. Prevention depends on education, safe blood, use of disposable needles and syringes, free distribution of condoms and early detection. In India, NACO (National AIDS Control Organisation) and other organisations work on awareness.
Cancer: in normal cells, contact inhibition stops cell growth when they touch other cells. Cancer cells lose this property and divide uncontrollably, forming tumours. Benign tumours stay confined to their original location and cause little damage. Malignant tumours grow rapidly, invade surrounding tissues, and cells can travel through blood to distant sites to form new tumours; this is metastasis. Carcinogens include ionising radiation (X-rays, gamma rays), non-ionising radiation (UV), chemical carcinogens in tobacco smoke, and oncogenic viruses with viral oncogenes. Cellular oncogenes (proto-oncogenes) in normal cells can be activated to cause cancer.
Detection uses biopsy and histopathology, blood and bone marrow tests, radiography (X-rays), CT and MRI, and antibodies against cancer-specific antigens. Treatment includes surgery, radiation therapy, chemotherapy and immunotherapy with biological response modifiers such as α-interferon.