HIV Flashcards
How is HIV spread
Sharing needles, unprotected sex, maternal transmission from mother to unborn child or in breast milk, direct blood-to-blood transfer through cuts and grazes
When is person with HIV considered to have AIDS
When immune system so weak that it can no longer fight off a range of diseases it would normally cope with/ T helper cell count drops below a certain level
What does AIDS stand for
Acquired immune deficiency syndrome
Structure of HIV virus
RNA surrounded by protein capsid enclosed in a layer of viral protein, lipid envelope formed from host cell membrane with viral glycoprotein molecules sticking through, also contains reverse transcriptase enzyme to generate DNA from its RNA
What type of cells to HIV invade and how
T helper cells, glycoprotein molecules (gp120) on virus surface bind to CD4 receptors on surface of T helper cells, envelope surrounding the virus fuses with T helper cell membrane and viral RNA enters the cells
How does HIV replicate new virus components once inside T helper cell
Virus uses enzyme reverse transcriptase to manufacture DNA from RNA template and the DNA is integrated into host’s DNA by enzyme integrase, once HIV genome integrated into host cells genome it can be transcribed and translated to produce new virus proteins.
How are new HIV viruses produced
New HIV virus proteins, glycoproteins and nuclear material are assembled into new viruses which bud out of the T cell and take some of the host cell surface membrane with them as envelope and kill the cell as they leave
How does infected person’s immune system become deficient due to HIV
Infected T helper cells are destroyed by T killer cells, so as number of viruses increases the number of host T helper cells decreases. Loss of T helper cells results in macrophages, B cells and T killer cells not being successfully activated and therefore not functioning properly
Describe the acute phase of infection
-HIV antibodies appear in blood after 3-12 weeks
-experience fever, sweats, headaches, sore throat and swollen lymph nodes or none
-rapid replication of the virus and loss of T helper cells
-after a few weeks infected T helper cells are recognised by T killer cells which start to destroy them which reduces rate of virus replication but does not totally eliminate it
Describe the chronic/latency phase of HIV
-may be no symptoms but there can be increasing tendency to suffer colds or other infections which are slow to go away
-dormant diseases eg TB can reactivate
Describe the disease phase
Increased number of viruses and declining number of T helper cells indicates onset of AIDS
-immune system vulnerable to other diseases (opportunistic infections) eg pneumonia and TB
-can be significant weight loss, dementia, tumours
