HIV & AIDS (SL IB Biology)

• Human Immunodeficiency Virus is a retrovirus
• The virus is unable to survive outside of the human body; it needs host cells in order to replicate
• HIV is not transmitted by a vector (unlike in malaria), it is spread by direct exchange of body fluids
• This means HIV can be transmitted in the following ways:
  • Sexual intercourse
  • Blood donation
  • Sharing of needles used by intravenous drug users
  • From mother to child across the placenta
  • Mixing of blood between mother and child during birth
  • From mother to child through breast milk

• HIV is made up of several key components including RNA and the enzyme, reverse transcriptase, which is used to produce DNA in the host cell; this classifies HIV as a retrovirus
• HIV infects the body and attacks a type of lymphocyte cell called a T-helper cell
• T-helper cells are a key component in the production of antibodies, so HIV inhibits the body's capacity to produce antibodies
• In the early stages of infection, antibodies are produced to fight HIV, these can be detected in blood tests
  • The individual is said to be HIV positive 

The development of AIDS

• As the infection progresses, the ability to produce antibodies significantly reduces
• This renders the immune system unable to fight off other pathogens and so the individual becomes prone to infection from other opportunistic pathogens
• When the individual is suffering from several diseases or conditions at the same time, they are said to have acquired immune deficiency syndrome (AIDS)
• Progression of HIV, from the initial infection to the development of AIDS, can be slowed down using anti-retroviral drugs
  • Due to highly successful drugs, many HIV positive individuals are able to live full-quality lives with normal life expectancies