HIV stands for human immunodeficiency virus. It is the virus that can lead to acquired immunodeficiency syndrome, or AIDS, if not treated. Unlike some other viruses, the human body can’t get rid of HIV completely, even with treatment. So once you get HIV, you have it for life.
Route of transmission of HIV virus
HIV is transmitted from person to person by the following ways.Sexual transmission (>75%)
More common among the male homosexuals than heterosexuals. HIV can be transmitted via:- Vaginal sex
- Anal sex
- Oral sex
Parenteral transmission
- By infected blood and blood products
- Contaminated needles, syringes, and surgical instrument
- Injectable drug abusers
Vertical transmission
- Trans-placental
- During birth through the birth canal
- Breast feeding
Probable other methods
HIV virus preferentially attacks and kills the white blood cells that contain a specific surface antigen, CD4 (for example, T cells, monocytes/macrophages).
These cells are vital for the maintanence of the immunity of the body against infection and malignant cells.
The pathogenesis can be summarized as:
- HIV enters the body through different routes (see above) and goes to the blood.
- In the blood HIV infects CD4+ T cells and kills them.
- T cells are directly responsible for cell mediated immunity and also indirectly responsible for humoral immunity (antibody mediated immunity) of the body.
- Destruction of T cell means destruction of cell mediated immunity and humoral immunity.
- As the immunity decreases, the body is now more prone and susceptible to infection by opportunistic pathogens.
- Leading to the development of opportunistic infections.
- AIDS.
HIV also infects the macrophages present in brain. These macrophages are called microglia.
Microglial cells, when infected by HIV, do not die as quickly as T cell.
But since they are infected by HIV they release abnormal chemicals which damage the nerve cells (neurons). This produces significant neurological sign and symptoms.
There are three main reason why our body can't kill the HIV virus:
- Integration of the viral DNA into the host cell DNA, resulting in a persisting infection.
- A high rate of mutation of the env gene (Read about the genetics of HIV).
- The production of the tat and nef proteins that down-regulates class 1 MHC proteins required for cytotoxic T-cell to recognize and kill HIV infected cells.
Differences between HIV 1 and HIV 2:
Points | HIV 1 | HIV 2 |
---|---|---|
Geographical distribution | World wide | In west Africa |
Virulence | More | Less |
Incubation period | Short | Long |
Tumor | Kaposi sarcoma is more | Not so common |
Opportunistic infection | Pneumocystic pneumonia | Cryptococcosis |
That's all for today!
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