Lecture 7.2: HIV

Question 1

What does HIV stand for?

Answer 1

Human Immunodeficiency Virus

Question 2

Structure of HIV (6)

Answer 2

Virus Envelope (Proteins)
Lipid Membrane
p17 Matrix Proteins
p24 (Core) Capsule Proteins
Reverse Transcriptase 
RNA

Question 3

How many genes does the HIV virus have?

Answer 3

9 Genes that encode 15 Proteins

Question 4

Types of HIVs (2): Subgroups and Demographics

Answer 4

HIV 1:
• Most common in sub-Saharan Africa and throughout the world
• Groups M, N, and O
• Pandemic dominated by Group M (comprised of subtypes A - J)

HIV 2:
• Most often found in West Central Africa, parts of Europe and India

Question 5

What does HIV do?

Answer 5

It destroys CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain infections and cancers

Question 6

What are the origins of HIV-1?

Answer 6

• HIV-1 originated in Central Africa in the first half of the 20th century
• A closely related chimpanzee virus first infected humans
• Related virus known as SIV (Simian Immunodeficiency Virus)
• HIV entered the human population from primates
• Probably occurred during butchering/consumption of monkey meat in Africa

Question 7

What are the origins of HIV-2?

Answer 7

• HIV-2 originated in sooty mangabeys

* It is responsible for fewer infections than HIV-1

Question 8

How is HIV Transmitted? (5)

Answer 8

• Unprotected sexual contact with an infected partner
• Exposure of broken skin or wound to infected blood or body fluids
• Transfusion with HIV-infected blood
• Injection with contaminated objects
• Mother to child during pregnancy, birth or breastfeeding

Question 9

HIV Life Cycle (7 Stages)

Answer 9

1) Binding (gp120 protein to CD4 receptor)
2) Fusion (endocytosis)
3) Reverse Transcription (via reverse transcriptase)
4) Integration (proviral DNA enters the host cell’s nucleus, integrase facilitates
the proviral DNA’s integration into the host’s DNA)
5) Replication (host cell then produces HIV RNA and HIV proteins)
6) Assembly (HIV proteins assembled into HIV virions & budded from cell
surface)
7) Budding (HIV protease cleaves viral proteins, converting the immature virion
to a mature, infectious virus)

Question 10

What are the 2 main consequences of HIV infection?

Answer 10

• Damage to the immune system, specifically depletion of CD4+ lymphocytes
• Immune activation

Question 11

What are are the 3 Stages of HIV Infection?

Answer 11

1) Acute HIV infection
2) Chronic HIV infection
3 Acquired Immunodeficiency Syndrome (AIDS)

Question 12

What is a normal CD4 count?

Answer 12

750/mcL

Question 13

At what CD4 count is immunity affected?

Answer 13

• Immunity is minimally affected if the count is >350/mcL
• Count drops below about 200/mcL, loss of cell-mediated immunity

Question 14

What is AIDS?

Answer 14

AIDS is the final stage of the disease caused by infection with a type of virus called HIV

Question 15

Other factors that increase transmission of HIV (7)

Answer 15

• A high plasma HIV viral load in the source
• Breaches in the mucosal barrier such as mouth or genital ulcer disease
• Trauma following sexual assault
• Menstruation or other bleeding may also facilitate transmission
• STIs enhance HIV transmission in epidemiological studies
• The risk of HIV transmission is likely to be greater if ejaculation occurs
• Non-circumcision may increase the risk of HIV acquisition

Question 16

Testing for Viral Infection

Answer 16

• Viral Load

* p24 Antigen

Question 17

Testing for Immune Response

Answer 17

• Antibody (IgG, IgM)
• Cellular response (CD4)

Question 18

How long before time from initial infection with HIV until antibodies are detected?

Answer 18

3-8 Weeks

Question 19

What are the 3 things AIDS are defined as?

Answer 19

• HIV infection that leads to any of certain AIDS-defining illnesses
• A CD4+ T lymphocyte (helper cell) count of < 200/mcL
• A CD4+ cell percentage of ≤ 14% of the total lymphocyte count

Question 20

What is an Aids Defining Illness?

Answer 20

Certain serious and life-threatening diseases that occur in HIV-positive people

Question 21

Examples of Aids Defining Illness

Answer 21

• Pneumocystis Pneumonia
• Kaposi’s Sarcoma
• Non-Hodgkin Lymphoma
• Encephalopathy
• Cytomegalovirus Retinitis
• Invasive Cervical Cancer
• TB
• Chronic Intestinal Cryptosporidiosis

Question 22

What is Kaposi’s Sarcoma? What is it caused by?

Answer 22

• A rare type of cancer caused by a virus
• Originates from endothelial cells
• As a response to infection by human herpesvirus type 8 (HHV-8)

Question 23

Features of Kaposi’s Sarcoma

Answer 23

• The tumours typically appear as painless purplish spots on legs, feet or face
• Blood Vessels grow in tangled mass
• Easily ruptured
• Skin
• Other organs

Question 24

How to screen for HIV? (7)

Answer 24

• ELISA
• Western blot
• PCR which is sensitive to extremely low HIV RNA levels
• The full testing sequence takes at least a day
• Particle agglutination
• Immunoconcentration
• Immunochromatography

Question 25

Treatment of HIV

Answer 25

• Antiretroviral therapy (ART) is the use of HIV medicines
• People on ART take a combination of HIV medicines
  (called an HIV Regime)
• These are taken daily
• HIV medicines can also reduce the risk of HIV Transmission

Question 26

How can HIV be prevented?

Answer 26

• Condom use
• Expanded HIV testing
• Prompt ART
• Use of PrEP

Question 27

What is PrEP?

Answer 27

• PrEP is a pill you can take to protect you from HIV
• Examples include Truvada
• PrEP offers you almost 100% protection from HIV, if you take it as instructed