AIDS and cancer

AIDS (Acquired Immuno Deficiency Syndrome) was first reported in 1981. It is caused by HIV (Human Immuno deficiency Virus), a retrovirus: its genetic material is RNA, which it copies into DNA inside our cells.

How it spreads: only through body fluids: sexual contact with an infected person, transfusion of contaminated blood, sharing infected needles (as drug users may do), and from an infected mother to her child through the placenta. It does not spread by touch, hugging, shaking hands, or sharing food. There is usually a long gap, from a few months to many years, between infection and the appearance of AIDS.

What it does: HIV enters macrophages. There, an enzyme called reverse transcriptase copies its RNA into DNA, which joins the cell's own DNA. The infected cell now keeps making new viruses: it becomes an 'HIV factory'. The new viruses attack helper T-lymphocytes, multiply in them and kill them. As the number of helper T-cells falls, the whole immune system fails, and the person suffers from infections that a healthy body would easily overcome, such as those caused by the bacteria Mycobacterium and the parasite Toxoplasma. A widely used test is ELISA. Anti-retroviral drugs can prolong life but cannot cure AIDS.

Prevention is the best weapon. NACO (National AIDS Control Organisation) and other bodies educate people. Key steps: use only safe blood for transfusion, use disposable needles, distribute condoms, control drug abuse, and encourage regular check-ups for people at risk. AIDS must be talked about openly, and people living with it should be treated with care, not shunned.

Cancer is one of the most feared diseases. Normal cells stop dividing when they touch other cells: contact inhibition. Cancer cells lose this control and keep dividing, forming masses of cells called tumours.

• Benign tumours stay in one place and do not spread.
• Malignant tumours grow fast, invade nearby tissue, and send cells through the blood to other parts of the body, where they form new tumours: metastasis. This is what makes cancer so dangerous.

Causes: agents called carcinogens can turn normal cells into cancer cells: ionising radiation (X-rays, gamma rays), UV light, chemicals (including those in tobacco smoke), and oncogenic viruses. Our cells contain genes called proto-oncogenes (c-onc), which, when activated in certain ways, can lead to cancer.

Detection: a biopsy (examining a thin piece of tissue under the microscope), blood and bone marrow tests, radiography (X-rays), CT and MRI scans, and antibodies against cancer-specific antigens. Treatment: surgery, radiotherapy, chemotherapy (drugs that kill cancer cells, though they have side-effects such as hair loss and anaemia), and immunotherapy: substances such as α-interferon activate the immune system to help destroy the tumour.