10 min readPathway sheet1-mark MCQ or assertion-reason, a 3-mark question on how HIV multiplies, a 5-mark answer on transmission, replication and prevention; also a NEET favourite

HIV and AIDS

AIDS is caused by HIV, a retrovirus that multiplies in macrophages and destroys helper T-lymphocytes, leaving the body open to infections. Prevention is the only answer.

AIDSAcquired Immuno Deficiency Syndrome; acquired during life, not congenital; first reported in 1981

HIVHuman Immunodeficiency Virus, a retrovirus with an envelope around its RNA genome

Key enzymeReverse transcriptase makes viral DNA from the viral RNA

Diagnosis and treatmentELISA test; anti-retroviral drugs, only partially effective

How HIV spreads, and how it does not

Sexual contact with an infected person.
Transfusion of contaminated blood and blood products.
Sharing infected needles, as among intravenous drug users.
From an infected mother to her child through the placenta.
High-risk groups: people with multiple sexual partners, intravenous drug users, people who need repeated blood transfusions, and children of HIV-infected mothers.
HIV does not spread by touch or physical contact; it spreads only through body fluids. So infected people must not be isolated from family and society.

How HIV destroys immunity

1
HIV enters the body and gets into macrophages.
2★
The viral RNA is copied into viral DNA by the enzyme reverse transcriptase.
3
Viral DNA is inserted into the host cell's DNA and directs the cell to make new viruses. The macrophage keeps making virus, acting as an HIV factory.
4
HIV also enters helper T-lymphocytes (TH cells), multiplies, and the new viruses attack more helper T cells.
5
The number of helper T cells falls steadily. The person has bouts of fever, diarrhoea and weight loss.
6
The person becomes so immunodeficient that they get infections that are normally overcome: bacteria such as Mycobacterium, viruses, fungi and parasites such as Toxoplasma.

★ key step

How to draw the replication of HIV

Draw a large host cell (macrophage) with a nucleus.
Outside it, draw a round HIV particle with an outer envelope and RNA inside; arrow: virus enters host cell.
Inside the cell write: viral RNA → viral DNA, with reverse transcriptase on the arrow.
Draw an arrow into the nucleus: viral DNA incorporated into host genome.
Draw arrows out: new viral RNA and viral proteins are made, and new viruses bud out of the cell.
Add a final arrow: new viruses infect other cells, including helper T cells.

Time lag, diagnosis and treatment

There is a time lag between infection and the appearance of AIDS symptoms. It may be a few months to many years, usually 5 to 10 years. During this time the person may look healthy but can pass on the virus. A widely used diagnostic test is ELISA (enzyme-linked immunosorbent assay). Anti-retroviral drugs are only partially effective: they can prolong life but cannot cure the disease.

Prevention

AIDS has no cure, so prevention is the best option; infection mostly follows conscious behaviour, unlike typhoid or pneumonia.
In India, the National AIDS Control Organisation (NACO) and NGOs educate people; WHO also runs programmes.
Make blood from blood banks safe by testing it for HIV.
Use disposable needles and syringes in all hospitals and clinics.
Free distribution of condoms, advocating safe sex, and controlling drug abuse.
Promote regular check-ups for HIV in high-risk groups, and talk about HIV openly without stigma.

In real life

Every unit of blood in an Indian blood bank is tested for HIV before transfusion. The red ribbon on World AIDS Day (1 December) reminds us that HIV does not spread by sharing food, hugging or sitting together.

Exam angle

2 marks: “Why is AIDS called an 'acquired' immunodeficiency syndrome? Name its causative agent.” The immune deficiency is acquired during a person's lifetime; it is not congenital. Syndrome means a group of symptoms. Agent: HIV, a retrovirus.

3 marks: “Explain how HIV multiplies in the human body and why the patient becomes immunodeficient.” HIV enters macrophages; reverse transcriptase makes viral DNA from RNA; viral DNA joins host DNA; macrophage becomes an HIV factory. Virus enters helper T cells, whose numbers fall; body cannot fight infections such as Mycobacterium and Toxoplasma.

5 marks: “Describe the modes of transmission of HIV, its replication in the body, and the steps taken to prevent AIDS.” Four routes; high-risk groups; not by touch. Replication through macrophages and helper T cells with reverse transcriptase. ELISA; anti-retroviral drugs. Prevention: safe blood, disposable needles, condoms, controlling drug abuse, NACO awareness.

Remember it

HIV goes RNA to DNA (reverse!), hides in the macrophage factory, and Takes down T helper cells.