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3.7.7Additional lessons

HIV and AIDS — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 6 of 101

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Part 1 of 4Transmission of HIV

3.7.7 HIV and AIDS
The virus
  • Human immunodeficiency virus is a retrovirus with an RNA genome, and it cannot survive for long outside the human body.
Body fluids
  • HIV passes from person to person by direct exchange of body fluids such as blood, semen, vaginal fluid and breast milk.
Common routes
  • Unprotected sex, shared needles and the transfer of blood are the main routes, and an infected mother can pass the virus to her baby.
No insect vector
  • Unlike malaria, HIV is not carried by a vector and is not spread by casual contact such as touching or sharing a room.
Prevention
  • Condoms, screening of donated blood, needle exchange and drugs given to mothers during pregnancy all lower the risk of transmission.

Part 2 of 4Effect on the Immune System

Helper T cells coordinate the adaptive response, so losing them weakens the whole system.

1
The virus enters the body and infects helper T cells, using proteins on their surface membrane to attach and gain entry.
2
Inside the cell, the viral RNA is copied into DNA by reverse transcriptase, and the DNA is inserted into the host genome.
3
The infected helper T cell makes new viral particles, which are released and go on to infect other helper T cells.
4
Over months to years the number of helper T cells falls, because infected cells die and are not replaced fast enough.
5
With few helper T cells, B cells and other lymphocytes are poorly activated, and the person becomes vulnerable to infections that a healthy person would resist.

Part 3 of 4HIV and AIDS

HIV and AIDS
HIV
  • This is the name of the virus that infects the host.
AIDS
  • Acquired immune deficiency syndrome is the group of illnesses that develop when the immune system has been badly weakened by HIV.
Opportunistic infections
  • Diseases such as tuberculosis, pneumonia and some cancers cause most of the deaths, not the virus directly.
Treatment
  • Antiretroviral drugs block steps in viral replication and allow many people to live a near-normal life span.
TermMeaning
HIVThe virus
HIV positiveAntibodies or virus detected in the blood
AIDSLate-stage syndrome of opportunistic infections
AntiretroviralDrug that interferes with viral replication

Part 4 of 4Exam Checklist & Tips

3.7.7 – Key Points for the Exam

  • Retrovirus A virus with an RNA genome that is copied to DNA by reverse transcriptase.
  • Helper T cell The lymphocyte type targeted by HIV.
  • AIDS Syndrome resulting from severe loss of immune function.
  • Opportunistic infection An infection that takes hold because the immune system is weak.
  • Antiretroviral A drug that slows viral replication.

Common Mistakes

  • Using HIV and AIDS as if they meant the same thing;
    • HIV is the virus and AIDS is the condition it can lead to.
  • Saying that HIV is spread by mosquitoes or by touching an infected person.
  • Claiming that antibiotics can treat HIV, since antibiotics act only on bacteria.
  • Stating that HIV directly kills the patient, when death usually follows opportunistic infections.

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