Q.Read the following passage and answer the questions that follow. In 1981, the health workers of United States of America had become aware of the increased frequency of Kaposi's sarcoma, cancer of the skin and blood vessels and another disease pneumocystis pneumonia, a respiratory infection caused by a protozoan. Both these diseases were very rare in the general population, but occurred frequently in more severely "immunosuppressed" individuals. This led to the recognition of the immune system disorder that was named Acquired Immune Deficiency Syndrome (AIDS). In 1983, virologists working in the USA and France had identified a causative agent for 'AIDS', now known as Human Immunodeficiency Virus (HIV). 'HIV' follows a set path to attack the human body to cause the disease.
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Start your 14-day free trial to unlock the full solution →Part (a): after gaining entry HIV first attacks macrophages, where reverse transcriptase makes viral DNA that integrates into host DNA and directs new virus production (the macrophage acts as an HIV factory); the virus later infects helper T-lymphocytes, whose numbers then fall. AIDS is diagnosed by ELISA and treated (not cured) by anti-retroviral therapy; WHO advises screened blood, disposable needles and safe sex.
Part (c): an AIDS patient dies of opportunistic infections/cancers, not of HIV itself, because immunity has collapsed.
The passage records how, in 1981, rising cases of Kaposi's sarcoma and pneumocystis pneumonia in immunosuppressed people revealed a new disorder, AIDS, whose cause — HIV — was identified by 1983.
Part (a)
(a) Target cells and the events within. After gaining entry into the body, HIV first attacks the macrophages. Inside a macrophage the sequence is:
- the viral RNA is released into the cell;
- reverse transcriptase converts the viral RNA into viral DNA;
- this viral DNA integrates into the host cell's chromosomal DNA;
- using the host machinery the infected macrophage produces new viral RNA and proteins, i.e. new virus particles;
- the macrophage keeps producing virus and so acts like an HIV factory. The virus subsequently enters helper T-lymphocytes (CD4+ T-cells / T_H cells), replicates in them and releases progeny viruses that go on to infect more helper T-cells. As a result the helper-T population falls steadily, weakening immunity.
(b) Diagnosis and treatment. The widely used diagnostic test is ELISA (Enzyme-Linked Immuno-Sorbent Assay), which detects antibodies made against HIV. There is no complete cure at present; the disease is managed with anti-retroviral therapy (ART / HAART) — a combination of drugs that suppress viral replication, slow progression and prolong the patient's life.
(c) Two WHO prevention steps.
- Ensure transfusion of only screened, HIV-free blood and blood products, and insist on disposable/sterile needles and syringes. …
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