MPSC 2026 Prelims Paper-I · Question 63 of 100

Correct — option (3). The whole point of this question is the distinction between being infected with HIV and having AIDS. HIV is the virus; AIDS, the Acquired Immuno Deficiency Syndrome, is the late clinical stage that follows once the virus has destroyed enough of the immune system. Trace the sequence the option set is built on. The virus enters the body and infects macrophages. Being a retrovirus, its genetic material is RNA, so it must first make a DNA copy of itself using its own enzyme, reverse transcriptase; that viral DNA is then inserted into the host cell's own DNA and turns the infected cell into a factory for new virus particles. The virus also enters helper T-lymphocytes, the cells that act as the master switch of the adaptive immune response, replicates inside them and releases progeny virus which goes on to attack still more helper T cells. Repeated round after round, this steadily drives down the number of helper T-lymphocytes in the body. It is only when that population has been depleted far enough that the person becomes unable to defend himself against organisms that would normally be harmless — and the bouts of fever, persistent diarrhoea, weight loss and opportunistic infections by bacteria, viruses, fungi and parasites appear. Those are the symptoms of AIDS. Every earlier step in the list is real, but silent. Note also how long this takes: the gap between infection and the appearance of AIDS is typically several years, commonly quoted as five to ten, and can run from a few months to many years.

• (1)When the infecting retrovirus enters host cells — This is the very first event of the infection, and it produces no AIDS. Entry into macrophages and helper T cells starts the process; it does not end it. Some people do experience a brief flu-like illness within a few weeks of acquiring HIV, but that is a short seroconversion illness, not the syndrome the question is asking about, and it resolves. Confusing the moment of infection with the onset of disease is exactly the error the option is placed here to catch, and it is the same error that makes people believe a person who 'looks well' cannot be carrying HIV.
• (2)When viral DNA is produced by reverse transcriptase enzyme — Reverse transcription is a molecular event inside a single infected cell — the RNA genome of the retrovirus being copied into DNA so that it can be integrated into the host chromosome. It is the step that gives retroviruses their name and it happens within hours of the virus entering a cell, long before any immune damage has accumulated. A biochemical step inside one cell cannot produce a whole-body syndrome; symptoms require the loss of a large fraction of the helper T-cell population. This option is attractive because it is the most technical-sounding line in the set, which is precisely why it deserves suspicion.
• (4)Within 15 days of sexual contact with an infected person — Wrong on the timing and wrong on the route. The interval between infection and the appearance of AIDS is typically measured in years, not days — a few months to many years, most often around five to ten. Fifteen days is in fact inside the 'window period', during which a newly infected person may still test negative on an antibody-based test while already being infectious. The option is also too narrow on transmission: besides sexual contact, HIV passes through transfusion of contaminated blood and blood products, through sharing of infected needles, and from an infected mother to her child through the placenta. Any option that fixes a short, precise deadline on a slow disease should be read twice.

HIV belongs to the group of viruses called retroviruses, which carry their genetic information as RNA and possess reverse transcriptase, an enzyme that copies RNA into DNA — the reverse of the usual flow of information in a cell. That DNA copy is spliced into the host cell's own genome, which is why the infection is lifelong: the viral instructions become part of the cell. The target that matters clinically is the helper T-lymphocyte. Helper T cells do not themselves kill infected cells or make antibodies; they instruct the cells that do. Removing them therefore disables the immune response broadly rather than against one germ, and that is what the word 'deficiency' in Acquired Immuno Deficiency Syndrome refers to. The illnesses that follow are called opportunistic infections because the organisms causing them — including mycobacteria, fungi and parasites such as Toxoplasma — take an opportunity created by the failed defence rather than being unusually virulent in themselves.

Transmission of HIV is limited to a small, well-defined set of routes: sexual contact with an infected person, transfusion of contaminated blood or blood products, sharing of contaminated needles, and passage from an infected mother to her child across the placenta. It is not spread by mosquitoes or other biting insects, nor by ordinary social contact — sharing food, shaking hands, using the same toilet — and correcting that misconception is a standing public-health objective. Diagnosis relies on detecting the body's antibody response, most commonly by the ELISA test, with a confirmatory test where required. Treatment uses anti-retroviral drugs which suppress the virus and prolong life substantially but do not eliminate the integrated viral DNA. In India the response is coordinated by the National AIDS Control Organisation (NACO) working with State AIDS Control Societies and non-governmental organisations.

• HIV is a retrovirus: its genome is RNA, and its enzyme reverse transcriptase makes a DNA copy which is integrated into the host cell's DNA, so the infection persists for life once established.
• The virus first multiplies in macrophages and then in helper T-lymphocytes; progressive destruction of helper T cells is what disables the immune system and produces AIDS. Infection with HIV and the disease AIDS are not the same stage.
• Typical interval between HIV infection and the appearance of AIDS: a few months to many years, most commonly quoted as five to ten years. During much of this period the person is infectious but shows no symptom.
• Symptoms of the AIDS stage include recurrent fever, persistent diarrhoea, marked weight loss, swollen lymph nodes and opportunistic infections by organisms that are normally harmless — bacteria, viruses, fungi and parasites such as Toxoplasma.
• Routes of transmission: sexual contact, transfusion of contaminated blood and blood products, shared contaminated needles, and mother to child across the placenta. Not by insect bite or by casual social contact. Diagnosis is usually by ELISA; treatment is with anti-retroviral drugs; the national programme is run by NACO.

• Equating HIV-positive status with AIDS. A person can carry and transmit HIV for years without any symptom; AIDS is the late stage that follows immune collapse.
• Believing HIV spreads through mosquito bites or ordinary social contact. Both are false and both appear regularly as statements in objective papers.
• Trusting an option that puts a short, precise deadline ('within 15 days') on a disease whose course is measured in years — and forgetting the window period, during which an antibody test can be negative in an already-infected person.

HIV and AIDS are asked from three angles and it pays to prepare all three. First, mechanism — which cell is attacked, which enzyme is used, what a retrovirus is, and the stage at which symptoms appear, which is this question's angle. Second, transmission and prevention, usually as a statement list where a false route such as insect bite is inserted among true ones. Third, symptoms and diagnosis, where the paper lists clinical signs and asks which belong to AIDS. Because the disease sits at the junction of biology and public health, both a science paper and a current-affairs paper can ask it, and the safest preparation is the full sequence — virus, target cell, latency, immune collapse, opportunistic infection, test, treatment, programme.

• practice — not a real PYQ

  The enzyme reverse transcriptase, characteristic of HIV and other retroviruses, catalyses which one of the following?

  • (a)Synthesis of RNA from a DNA template
  • (b)Synthesis of DNA from an RNA template
  • (c)Synthesis of protein from an RNA template
  • (d)Breakdown of the host cell membrane

  Answer(b) Synthesis of DNA from an RNA template — the reverse of the usual flow of genetic information, which is what gives retroviruses their name. The DNA copy so made is then integrated into the host cell's own genome, and that integration is why HIV infection cannot be cleared once established.

• practice — not a real PYQ

  Which one of the following cells of the human immune system is the principal target of HIV, and whose depletion produces the immunodeficiency of AIDS?

  • (a)Erythrocytes
  • (b)Helper T-lymphocytes
  • (c)Platelets
  • (d)Neutrophils

  Answer(b) Helper T-lymphocytes — they coordinate both the antibody-mediated and the cell-mediated arms of acquired immunity, so their loss disables the defence broadly rather than against a single organism. The resulting opportunistic infections, not the virus itself, are what kill.