Lecture 7.2: HIV Flashcards
What does HIV stand for?
Human Immunodeficiency Virus
Structure of HIV (6)
Virus Envelope (Proteins) Lipid Membrane p17 Matrix Proteins p24 (Core) Capsule Proteins Reverse Transcriptase RNA
How many genes does the HIV virus have?
9 Genes that encode 15 Proteins
Types of HIVs (2): Subgroups and Demographics
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
What does HIV do?
It destroys CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain infections and cancers
What are the origins of HIV-1?
- 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
What are the origins of HIV-2?
- HIV-2 originated in sooty mangabeys
* It is responsible for fewer infections than HIV-1
How is HIV Transmitted? (5)
- 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
HIV Life Cycle (7 Stages)
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)
What are the 2 main consequences of HIV infection?
- Damage to the immune system, specifically depletion of CD4+ lymphocytes
- Immune activation
What are are the 3 Stages of HIV Infection?
1) Acute HIV infection
2) Chronic HIV infection
3 Acquired Immunodeficiency Syndrome (AIDS)
What is a normal CD4 count?
750/mcL
At what CD4 count is immunity affected?
- Immunity is minimally affected if the count is >350/mcL
- Count drops below about 200/mcL, loss of cell-mediated immunity
What is AIDS?
AIDS is the final stage of the disease caused by infection with a type of virus called HIV
Other factors that increase transmission of HIV (7)
- 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
Testing for Viral Infection
- Viral Load
* p24 Antigen
Testing for Immune Response
- Antibody (IgG, IgM)
- Cellular response (CD4)
How long before time from initial infection with HIV until antibodies are detected?
3-8 Weeks
What are the 3 things AIDS are defined as?
- 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
What is an Aids Defining Illness?
Certain serious and life-threatening diseases that occur in HIV-positive people
Examples of Aids Defining Illness
- Pneumocystis Pneumonia
- Kaposi’s Sarcoma
- Non-Hodgkin Lymphoma
- Encephalopathy
- Cytomegalovirus Retinitis
- Invasive Cervical Cancer
- TB
- Chronic Intestinal Cryptosporidiosis
What is Kaposi’s Sarcoma? What is it caused by?
- 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)
Features of Kaposi’s Sarcoma
- The tumours typically appear as painless purplish spots on legs, feet or face
- Blood Vessels grow in tangled mass
- Easily ruptured
- Skin
- Other organs
How to screen for HIV? (7)
- 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
Treatment of HIV
- 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
How can HIV be prevented?
- Condom use
- Expanded HIV testing
- Prompt ART
- Use of PrEP
What is PrEP?
- 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
