How Human Viruses are Transmitted and Cause Disease

Question 1

What is the definition of incidence?

Answer 1

number of new infections over a period of time

Question 2

What is the definition of prevalence?

Answer 2

total number of infections in a population, new and old, over period of time

Question 3

What is the definition of an endemic?

Answer 3

normal number of cases in a population
- number can be high, low, or even seasonal

Question 4

What is the definition of an epidemic?

Answer 4

an increase in the average number of cases in an area

Question 5

What is the definition of a pandemic?

Answer 5

an epidemic that has spread to several countries or counties

Question 6

What is the definition of reproductive number (Ro)?

Answer 6

• on average, how many people one infected person will infect in a susceptible population
• changes, want it small

Question 7

What is the definition of communicable?

Answer 7

• an infectious disease from one source to another
  ex: person to person, animal to person

Question 8

What is the definition of contagious?

Answer 8

• derived from contact
• ex: respiratory droplets, fecal/oral, contact with skin

Question 9

Which is farther spread: droplet or aerosol?

Answer 9

aerosol travels the longer distance

Question 10

What are non-contagious diseases?

Answer 10

• still contagious but have to have more than casual contact to be contagious
• ex: sexual contact, injection, congenital, perinatal, zoonotic, arboviral (mosquito)

Question 11

Is HIV an contagious or non-contagious disease?

Answer 11

non-contagious

Question 12

What is seasonality in regards to viral spread?

Answer 12

• many viral infections have a seasonal spike where population is more susceptible
• ex: winter/spring is season fro many viruses that are enveloped and transmitted through respiratory route (influenza)

Question 13

Which viruses have a peak season in summer/early fall?

Answer 13

• arboviruses (peak in insect vectors)

Question 14

What viruses do not have a seasonality?

Answer 14

• viruses spread through sexual contact or needle sharing

Question 15

What is the incubation period?

Answer 15

• time from infection until you get symptoms

Question 16

What is the latent period?

Answer 16

• time from getting infection until you become infectious

Question 17

What is the prodromal phase?

Answer 17

• generalized symptoms that can occur in many viral infections before specific symptoms arise that might aid in diagnosis

Question 18

What are the factors the determine severity of infection?

Answer 18

• age (sometimes young and elderly are more susceptible)
• immune status
• genetics of host

Question 19

What is the most common form of transmission?

Answer 19

• human to human

Question 20

What is zoonotic spread?

Answer 20

• spread of disease from non-human reservoir to human host

Question 21

What is the difference between horizontal and vertical transmission?

Answer 21

• horizontal: person to person spread (normal)
• vertical: parent to offspring

Question 22

What are the differences between localized and generalized/systemic infections?

Answer 22

Localized:
- doesn’t spread through body (skin, respiratory tract, GI tract, eye)
- shorter incubation times, usually days
- IgA usually more important
- not always lifelong immunity, sometimes shorter mucosal immunity

Generalized/Systemic:
- spreads through body via viremia (virus in blood) or nervous system
- longer incubation times, usually weeks to months
- IgG more important because in blood
- usually lifelong immunity

Question 23

What are acute infections?

Answer 23

• most infections
• cleared by immune system and can lead to lifelong immunity

Question 24

What are latent infections?

Answer 24

• infections hid in immune cells preceded by acute infections

Question 25

What is the definition of an epidemic?

Answer 25

an increase in the average number of cases in an area