Virology 2: Epidemiology and transmission of Viral Diseases Flashcards
(53 cards)
Define viral epidemiology. List the three terms used to describe.
Disease in population that develops before recognition of causative agents.
1. Endemic
2. Epidemic
3. Pandemic
Define endemic
Multiple/continuous transmission in a population/region/time
Define epidemic
widespread occurrence of an infectious disease in a community at a particular time. Exceeding the endemic baseline.
Define Pandemic
Worldwide epidemic
Define rate and how to calculate
Disease in a population.
Number of cases/population
Define Incidence or “attack rate” and how to calculate
- Case to population ratio.
- Number of cases/Population over a period of time (i.e person-years)
- Acute/Short-duration diseases will have incidence
Parameters that define incidence in acute diseases
Three in acute disease (short-duration)
1. Proportion of the population which is susceptible (S/P)
2. Proportion of the infected susceptible individuals (I/S)
3. Proportion of the diseased infected individuals (C/I)
Attack Rate VS Incidence parameters
See image. The Parameters allow you to more clearly identify the incidence and rate among a specified population.
Parameters that define incidence in viral diseases
- Case/infection ratio: proportion of infections resulting in clinical disease
- Case/fatality ratio: proportion of infection resulting in lethal disease
Define Prevalence and how to calculate
“Picture” of disease.
- Onset of unknown date so no time parameters.
- Number of current cases/population.
- Chronic, long duration diseases
Characteristics of data regarding epidemiology
Difficult to acquire, Often incomplete and inaccurate, Easier to compute.
Surveillance of disease
Continuous reporting and monitoring for growth of data
Serological survey definition
Antibody data; subjects were clinical disease silent (No clinical signs).
Not informative for current infection rate
what are prospective studies?
tracking events that are supposed to happen in the future. (i.e: placebo and treatment groups)
*Expensive
What are characteristics of retrospective studies?
Tracking past events, only need a limited number of subjects
*cost effective
Steps through viral infection of an individual
Incubation period, Generation time, period of infectivity, infection
When is the incubation period?
Moment of infection to onset of clinical signs
When is the generation time?
From moment of infection to first day of shedding virus. Usually shorter than incubation period.
When is the period of infectivity?
First day of shedding to last day of shedding. Influences spread of disease.
What are characteristics of a chronic viral disease and steps through the viral lifespan?
Distinction between each period is difficult to asses.
-Little correlation among disease, generation time, infectivity.
Modes of transmission by viruses
Horizontal
Vertical
Zoonotic
Vector-borne
Iatrogenic
Nosocomial
What is Horizontal Transmission and types of contact?
With or without a vector and between same or different species.
- Direct contact
- Indirect contact
- Airborne
Airborne examples
Droplets, aresols.
Indirect contact example and what type of virus is usually spread?
Indirect contact: Fomites, easting, bedding, vehicles, needles. Usually non-enveloped viruses.
— Common vehicles: Water, feed
