11 SIR model and HIV/AIDS

Question 1

R0 =
If I present you with a scenario in which I give you information on contacts (c), transmissibility (β), and recovery rate (γ), be able to use the equation R0 = c × β / γ to calculate R0

Answer 1

c × β / γ or R0 = c × β × D (because D = 1 / γ)

Question 2

R0, the “basic reproductive number,” is the number of … what?

Answer 2

the estimated number of people that will become infected from one/each infected person

Question 3

Be able to answer the following questions about R0 for an infectious disease that spreads through respiratory droplets, such as the flu or covid …
For each of the following interventions …
Would the intervention reduce contacts (c)? Why/how?
Would the intervention reduce transmissibility (β)? Why/how?
Would the intervention increase recovery rate (γ)? Why/how?
Interventions to consider …
- Hand washing
- Staying at home if symptomatic
- Vaccinations for people who have not been infected
- Becoming partially immune against a repeat infection after recovering from initial infection
- Mask-wearing
- Physical distancing
- Treatments for people who are infected

Answer 3

Practice Write it out

Question 4

What is the full name and acronym of the pathogen that causes AIDS? Is this pathogen a virus, bacteria, or parasite?

Answer 4

HIV Human immunodeficiency virus
AIDS Acquired immunodeficiency syndrome
- virus

Question 5

List 4 common modes of transmission of HIV infection.

Answer 5

blood, bodily fluids, sexual contact, dirty needles

Question 6

What type of human cell does HIV preferentially infect?

Answer 6

CD4+ cells these are immune system cells

Question 7

Why does untreated HIV infection cause immune deficiency, or loss of immune system function?

Answer 7

destroying specific white blood cells called CD4 positive (CD4+) T cells that are vital to fighting off infection. The resulting shortage of these cells leaves people infected with HIV vulnerable to other infections and diseases, and additional complications.

Question 8

What happens to the CD4 cell level in the blood during the acute, chronic, and AIDS stages of HIV infection? (In other words, describe how the level goes up or down over time; assume that level of CD4 cells is high in an uninfected person)

Answer 8

CD4 cells are reduced precipitously in acute HIV infection, but usually rebound in the blood over several weeks as HIV-specific CD8 T cells help to lower plasma viremia [7]. In the untreated patient, CD4 T cells subsequently decline over several years.
A CD4 count of 200 or fewer cells per cubic millimeter

Question 9

What happens to HIV viral load level in the blood during the acute, chronic, and AIDS stages of HIV infection? (In other words, describe how the level goes up or down over time; assume that level of HIV virus is zero in an uninfected person)

Answer 9

In the acute stage of infection, HIV multiplies rapidly and spreads throughout the body.
Chronice: HIV continues to multiply in the body but at very low levels.
People with AIDS can have a high viral load and may easily transmit HIV to others.

Question 10

The first treatment ever developed for HIV infection was Zidovudine, a nucleoside analog reverse-transcriptase inhibitor. By what mechanism of action does this medication reduce viral replication inside the CD4 cells? (Be able to explain in a few sentences what specific process the drug disrupts and how it does so.) See “how it works” video in class slides, the slide about Zidovudine.

Answer 10

It is a reverse transcriptase inhibitor
targets the replication stage of reverse transcription in the virus.
the drug imitates a nucleoside, but then blocks the next nucleoside from attaching and abruptly stops the process of replication within the human cell.