Epidemiology Flashcards
Virus epidemiology
The study of determinants, frequency, dynamics, and distribution
Why study epidemiology of viral diseases
Risk of infection and/or disease in an animal or population determined by:
- characteristics of virus (genetic variation from evolution)
- Host and host pop (passive, innate, acquired resistance)
- behavioral, environmental, ecological factors that affect virus transmission from one host to another
Role of epidemiology in viral diseases
Identify and/or clarify role of viruses in etiology of diseases
Understand interaction of viruses with environmental determinants of disease
Determining factors affecting host susceptibility
Studying impacts of viral disease on health, economy, and society
Unraveling modes of viral disease transmission
Studying role of infectious pathogens in pathogenesis of chronic non communicable diseases
Large scale testing of vaccines and drugs
How that helps
Advancing our understanding of nature of diseases
Alerting and directing disease treatment, control, and prevention activities
Providing early warning systems and tracking the disease
Assessment of economic and social impacts of a disease
Assessment of the efficacy and cost of disease control and prevention programs
Case fatality rate
Number (%) of deaths among the clinically ill animals
Mortality rate
Number (%) of animals in a population that die from a particular disease over a specified time period
Morbidity rate
Percentage of animals in a population that develop CS attributable to a particular virus over a defined period of time (commonly the duration of the outbreak)
Incidence
The number of new cases that occur in a population over specified period of time
Measure of the occurrence of infection or disease in a pop over time.
Prevalence
Number of occurrences of disease (old and new), infection, or relating attributes (antibodies) in a pap at particular point in time
Sporadic viral diseases
Viral diseases occurring occasionally, singly, or in scattered instances, and in an irregular and haphazard manner
Enzootic viral diseases (endemic in humans)
Constant presence of a viral disease within a given geographic area or population group
Epizootic viral diseases (epidemic in humans)
Occurrence of more cases of viral diseases than expected in a given area or among a specific group of people/animals over a particular period of time
refers to peaks in disease incidence that exceed that endemic/enzootic baseline or expected incidence of disease
Panzootic viral diseases (pandemic in humans)
Virus epidemic occurring over a very wide area (several countries or continents) and usually affecting large proportion of the population
Asymptomatic carrier
Animals that have contracted an infectious viral disease, but display no clinical symptoms
- shed virus, transmitting disease to others
- shedding of virus may be continuous or intermittent
Contagious disease
Disease that is spread from on person or organism to another by direct or indirect contact
Period of contagiousness
Time during which an infected animal sheds virus
Exotic disease
Disease not known to occur in a particular country of geographical area
Methods to study epidemiology of viruses- Seroepidemiology
Simply denotes the use of serological data as the basis of epidemiological investigation, as determined by diagnostic serological techniques
Methods to study epidemiology of viruses- Molecular epidemiology of viruses
The use of molecular biological data as the basis of epidemiological investigation of viral diseases
Transmission of viruses
Horizontal -Contact: direct and indirect -Vector: mechanical and biological -Vehicle borne -Iatrogenic -Nosocomial Vertical
Horizontal (lateral) transmission
Spread of an infectious agent from one person/animal or group to another person/animal or group
Most are transmitted this way
Contact transmission
Spread of infectious agent by direct or indirect contact
Direct contact transmission
Involves actual physical contact between an infected animal and a susceptible animal (rubbing, licking, biting)
Also includes sexual contact
Droplet transmission
Direct-contact
Transmission of virus in droplet nuclei (saliva or mucus) that travel less than 1 meter from the source to the susceptible host
Indirect contact transmission
Occurs via fomites, such as shared eating containers, bedding, etc
Fomite
Inanimate object or substance that is contaminated with infectious agent and is capable of transmitting infectious organisms from one individual to another
Airborne transmission
Indirect
Spread of infectious agents by droplet nuclei in dust that travel more than on meter sometimes for miles, from the infected to the susceptible host
Vector transmission
Athropod-borne
Athropod vectors carry viruses from infected host to susceptible host
Mechanical transmission
Passive transport of the infectious agent on the feet or other body parts of the arthropod vector
Biological transmission
Infectious agent undergoes either a necessary part of its life cycle, or multiplication, in the vector before transmission to susceptible host
Arboviruses
Class of viruses transmitted to humans by arthropods such as mosquitos and ticks
Enzootic transmission cycle
Sylvatic/jungle cycle
Natural transmission of virus between wild animals/birds (vertebrate hosts) and primary insect vectors
Epizootic transmission cycle
Rural cycle
Virus is transmitted between non-wild or domestic animals and the primary or accessory insect vectors
Urban transmission cycle
Virus cycles between humans and insect vectors
Amplifying host
In which the level of virus can become high enough that an insect vector such as a mosquito that feeds on it will probably become infectious
Dead-end host/incidental host
Host from which infectious agents are not transmitted to other susceptible hosts
Do not develop sufficient viremia to be picked up by the insect vectors
Common-vehicle transmission
Includes fecal contamination of food and water supplies (fecal oral transmission) and virus contaminated meat or bone products
Iatrogenic transmission
Infection that is transferred during medical or surgical practice
2 ways:
-intro of pathogens by contaminated instruments (non-sterile surgical instruments, syringes) or contaminated body surface (inadequate handwashing)
-intro of pathogen through contaminated prophylactic therapeutic prep
Nosocomial transmission
While an animal is in a vet hospital or clinic
Hospital acquired infection
Vertical transmission
Usually used to describe infection that is transferred from dam to embryo, fetus, or newborn before, during, or shortly after parturition (colostrum, milk, or fecal contamination of teats)
Zoonosis
Describes infections that are transmissible from animals to humans
Physical stability of virus
Viruses that are transferred by respiratory route have low environmental stability,
Transmitted fecal-ral have higher
Herd immunity
Occurs when the vaccination fo a significant large portion of a population provides measure of protection for individuals who have not developed immunity
Incubation period
Interval between infection and onset of CS
Many diseases have period during which animals are infectious before becoming sick
Prodromal period
First signs and feelings of illness after incubation period
Period of early symptoms of a disease occurring after incubation period and just before appearance of the characteristic symptoms of disease
Acute period
When disease is at its height
severe CS
Decline period
Period when CS begin to subside
Convalescent period
Body gradually returns to pre-diseases state, and health restored
