Epidemiology

Question 1

What is epidemiology?

Answer 1

The study of the cause, distribution, control, and prevention of disease in a population

Question 2

What does distribution mean in terms of epidemiology?

Answer 2

host range (limited or broad)

Question 3

What do epidemiologists study?

Answer 3

• mechanisms of viral transmission
  
  • risk factors for infection (triad model)
  • size of the population needed for virus transmission
    viruses love a crowd
  • geography
  • seasonal factors
  • means of control

Question 4

What is the triad model of epidemiology?

Answer 4

Three factors that influence disease caused by viruses

- host, pathogen, environment

Question 5

Talk about HIV and Influenza.

Answer 5

Both RNA viruses

• HIV RNA Retrovirus
• Influenza: segmented (-) RNA virus (each different segment codes for different protein)

Question 6

What is hemaglutinin and neuraminidase?

Answer 6

• hemagluttinin: enables entry by binding sialic acid on cell surface and plays role in release from endosome (M2 ion channel for H+ protons)
• neuraminidase: enzyme that enables release from cell cleaves sialic acid molecules on surface so hemaglutinin doesn’t rebind

Question 7

What is prevalence?

Answer 7

number of EXISTING cases total population or group

Question 8

What is incidence?

Answer 8

Number of NEW cases (usually new cases per year)

Question 9

What is the host range of influena?

Answer 9

horses, seals, birds, pigs, humans

Question 10

What are the features of influenza?

Answer 10

Influenza has a short INCUBATION PERIOD within the host

Time from infection to symptoms is approximately 1 to 2 days

Infected individuals act as ACUTE CARRIERS and spreaders of the virus

Infected individuals readily TRANSMIT the virus by coming
into contact with un-infected individuals or by expelling the
virus into the environment in the form of FOMITES (for example by sneeezing and coughing)

Question 11

How is influenza transmitted?

Answer 11

animal host to animal host and via fomites

Question 12

What are the factors that influence the spread of influenzaviruses?

Answer 12

Population density (more dense the better)

Close contact with infected wild and/or domestic animals (transmission from other species to human)

Herd immunity (vaccinated or unvaccinated population)

Migratory patterns of infected birds (avian flu)

Public Health Programs/Disease surveillance
(rapid identification of new strains)

Question 13

What are the strategies to reduce influenza transmission?

Answer 13

Vaccination

Good disease surveillance

Identification of disease outbreak

Potential quarantine

Antiviral drug development

Question 14

What opportunistic infections are immunocompromised people opened up to?

Answer 14

Kaposi’s sarcoma (KS)

Candidiasis (thrush)

Pneumocystis carinii pneumonia (PCP)

Question 15

When researchers were searching for the cause of the disease referred to as the “gay cancer” or gay-related immunodeficiency disease (G.R.I.D.), what did they know?

Answer 15

1) Each patient was immunocompromised
2) High mortality rate approaching 100%
3) Primarily gay men afflicted with disease
4) No treatment

Question 16

When researchers were searching for the cause of the disease referred to as the “gay cancer” or gay-related immunodeficiency disease (G.R.I.D.), what were their Theories about etiology of disease?

Answer 16

1. Amyl nitrates (poppers) used as sexual stimulants
2. STD (viral, bacterial, fungal?)
3. Environmental agent/factor
4. Multiple others

Question 17

What data collected by clinicians and scientists leads to the conclusion that GRID is caused by a pathogen?

Answer 17

1) Heterosexuals dying from disease (first reports in Haitian immigrants)
2) The epidemiology of the disease (pattern of spread) suggests that the etiologic agent of disease is transmissible (virus or bacteria)
3) People infected via blood transfusions, many hemophiliacs contract the disease

Question 18

What are the four H’s of ppl infected w/ HIV?

Answer 18

Homosexuals
Haitains
Hemophiliacs
Heroin Users

Question 19

What are the reservoirs of HIV and how is it spread?

Answer 19

Humans are the main RESERVOIRS of HIV

HIV is spread by CHRONIC carriers of HIV
- chronic/persistent infection

These carriers are asymptomatic due to the LONG
INCUBATION PERIOD of HIV thus they can readily
transmit the virus to others

Question 20

What is the pathogenesis of HIV?

Answer 20

Disease Phases:

• Acute (1 to 2 months)
• flu or mono-like symptoms

Asymptomatic (8 to 10 years)

• “clinical latency”
• immune system in constant battle with HIV

AIDS (Acquired Immune Deficiency Syndrome)

• immunodeficiency (<200 CD4+)
• diseases of nervous, respiratory, and gastrointestinal systems
• opportunistic infections (KS, PCP, thrush)
• death

Question 21

What are the viral targets of HIV? How is viral load measured?

Answer 21

CD4+ T-cells

• adaptive immune Response
• provide help to B cells and CD8+ T Cells
• prime target for HIV

HIV binds CD4+ receptor to get into T Cell

• initial drop in CD4+ T cells and recovery
• slow/steady decline of CD4+ T Cells as HIV kills them off

HIV RNA = viral load in patient
-initial increase in viral load then clinical latency

Question 22

Go over human host to human host HIV transmission.

Answer 22

1) Humans are the sole reservoir

2) Spread by direct contact with
     HIV-infected cells, blood, semen

3) Modes of transmission
        - intimate contact (STD)

          - i.v. drug use
          - mother to child
                in utero
                breast-feeding

Question 23

What are the Factors Positively influencing HIV transmission?

Answer 23

Presence of other STDs

Risky behaviors

  - iv drug use (needle sharing)
  - number of partners 

Education (negative influencer)

Geopolitical
- poverty, wars, migration

Question 24

What are the Strategies to reduce HIV PREVALENCE?

Answer 24

Development and use of effective
anti-retroviral therapies

2) Increased access to and affordability of
life-saving drugs

3) HIV/AIDS education

4) Vaccine?
may have to develop multiple HIV
vaccines against various HIV strains