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At which stage of HIV infection does one usually show symptoms of AIDS?
A
Within 15 days of sexual contact with an infected person
B
When the infecting retrovirus enters host cells
C
When viral DNA is produced by reverse transcriptase
D
When HIV replicates rapidly in helper T-lymphocytes and damages large number of these
Detailed Solution
After entering the body, HIV enters macrophages, where its RNA genome is copied into viral DNA by reverse transcriptase; this DNA is incorporated into the host DNA and directs the production of new virus particles. The macrophages act as an HIV factory.
At the same time HIV enters helper T-lymphocytes ($T_H$ cells), replicates and produces progeny viruses, which attack other helper T-cells.
This is repeated, leading to a progressive decrease in the number of helper T-lymphocytes.
During this period the person suffers from bouts of fever, diarrhoea and weight loss, and becomes so immuno-deficient that infections by $Mycobacterium$, viruses, fungi and parasites like $Toxoplasma$ cannot be resisted; these are the symptoms of AIDS.
There is always a time lag between infection and the appearance of symptoms, usually of 5–10 years, so the symptoms do not appear within 15 days or at the moment of viral entry or reverse transcription.
Hence the symptoms appear when HIV replicates rapidly in helper T-lymphocytes and damages a large number of them.
At the same time HIV enters helper T-lymphocytes ($T_H$ cells), replicates and produces progeny viruses, which attack other helper T-cells.
This is repeated, leading to a progressive decrease in the number of helper T-lymphocytes.
During this period the person suffers from bouts of fever, diarrhoea and weight loss, and becomes so immuno-deficient that infections by $Mycobacterium$, viruses, fungi and parasites like $Toxoplasma$ cannot be resisted; these are the symptoms of AIDS.
There is always a time lag between infection and the appearance of symptoms, usually of 5–10 years, so the symptoms do not appear within 15 days or at the moment of viral entry or reverse transcription.
Hence the symptoms appear when HIV replicates rapidly in helper T-lymphocytes and damages a large number of them.