Epidemiology Of Viral Diseases Flashcards
Describe virus epidemiology.
-study of determinants, freq, dynamics, distribution of viral disease in pop
Describe why we should study epidemiology of viral diseases.
Risk of inf/disease in animals & their pop is determined by:
1. Characteristics of virus (ex. Genetic variation from evolution)
2. Host & host pop (ex. Passive, innate, acquired resistance)
3. Behavioral, environmental, ecological factors that affect virus transmission from one host to another
Describe the role of epidemiology in viral diseases.
- ID & clarify the role of viruses in the etiology of diseases
- Understand the interaction of viruses w environmental determinants of disease
- Determining factors affecting host sus
- Unravel modes on viral disease transmission
- Study impact of viral disease on health, economy, society
- Study role of inf pathogens in pathogenesis of chronic non communicable disease like oncogenic virus in cancer
- Lg scale testing of vaccines & drugs (ex. Clinical trials)
Describe how epidemiology helps.
- Adv our understanding of nature of diseases
- Alert & direct disease treatment, control & prevention activities
- Provide early warning system & track disease
- Assess economic & social impacts of disease
- Assess efficacy & cost of disease control & prevention programs
Describe the different rates based on outcome of disease in population.
- Case fatality rate: # or % of deaths in clinically ill animals
-animal pop = 100
-sick pop = 25
-dead pop = 10
-case fatality rate = 10/25 x 100 = 40% - Mortality rate: # or % of animals in pop that die
-animal pop = 100
-sick pop = 25
-dead pop = 10
-mortality rate = 10/100 x 100 = 10% - Morbidity rate: % of animals in pop that develop CS to a virus over time (duration of outbreak)
Describe incidence VS prevalence based on duration/freq of occurrence.
- Incidence: # of new cases in a pop
-‘attack rate’ = measure of occurrence of inf/disease in pop over time
-useful for describing acute disease of short duration - Prevalence: # of occurrences of disease (old & new), inf, or related attributes (antibodies) in a pop at a particular time
Describe the 4 different types of viral diseases.
- Sporadic
-occur occasionally, singly, or scattered in a irregular manner - Enzootic (endemic in humans)
-constant presence in a geographic area or pop - Epizootic (epidemic in humans)
-more cases of a viral disease than expected in a area or pop over a period of time
-peaks in disease incidence that exceed endemic/enzootic baseline or expected incidence of disease - Panzootic (pandemic in humans)
-wide area affecting lg portion of pop
Describe asymptomatic carriers.
-animals that have contracted an inf viral disease but no CS
-shed virus & transmit disease to others
>continuous of intermittent
Describe the different types of asymptomatic carriers.
- Incubatory (acute)
-shed virus during incubation period of diease - Convalescent (chronic)
-shed virus during recovery from disease - In apparent
-carrier state may exist w an inf that’s in apparent thruout its course
Describe contagious disease VS exotic disease.
- Contagious
-disease spread from 1 person/organism to another by direct or indirect contact
>period of contagiousness = time during an inf animal sheds virus - Exotic
-disease not known to occur in a geographical area
Describe the 2 methods to study epidemiology of viruses.
- Seroepidemiology
-use of serological data as basis of epidemiological investigation as determined by diagnostic serological techniques - Molecular epidemiology
-use of molecular biological data as basis of epidemiological investigation of viral diseases
Describe the transmission of viruses.
Horizontal: most viruses spread of inf agent from one person/animal or group to another
1. Contact
A) direct
>bites, licking, coitus, droplets
B) indirect
>airborne, fomites
2. Vector
>mechanical or biological
3. Vehicle borne
4. Iatrogenic
5. Nosocomial
Describe contact transmission.
spread of inf agent by direct/indirect contact
1. Direct
-actual physical contact between inf & sus (ex. Licking, rubbing, biting)
-sexual
-droplet: transmission of virus in droplet nuclei (saliva or mucus) that travel less than 1m from source to sus host
>sneeze, cough
short distance travel so not considered as air borne
2. Indirect
-via fomites: inanimate object/substance thats contaminated w inf agent & capable of transmitting inf organisms from one individual to another
>ex: shared eating containers, bedding, dander, restraint device, vehicles, clothing, improperly sterilized surgical equipment, syringes, needles
-air borne: spread of inf agent by droplet nuclei in dust that travel more than 1m from the inf to the sus host
Describe vector transmission.
‘Arthropod borne transmission’
-arthropod vectors carry the virus from inf host to sus host
Describe a mechanical transmission example.
-mosquitos & other biting insects are mechanical vectors for fowlpox virus
Describe biological transmission.
-arthropod vector acquires virus by feeding on blood of viremic animal
-replication of ingested virus initially in insects gut -> spread to salivary gland takes days = ‘extrinsic incubation period’
-virions in salivary secretions of vector are inj into new animal host during blood meals
-helps virus to cross species barriers
Describe transovarial VS trans-stadial transmission in biological transmission.
- Transovarial
-virus transmitted from mother tick thru inf eggs to next gen of ticks - Trans-stadial
-virus transmitted from larva or nymph to next stage of development (nymph or adult)
-not transmitted vertically (mother tick to egg & next gen)
-ex: tick borne flavivirus
Describe arboviruses in biological transmission.
-class of virus transmitted to humans by arthropods like mosquitos & ticks
Describe the types of transmission cycles in arboviruses.
- Enzootic (sylvatic or jungle cycle)
-natural transmission of virus between wild animals/birds (vertebrate hosts) & primary insect vectors - Epizootic (rural cycle)
-virus transmitted between non wild or domestic animals & primary or accessory insect vectors - Urban cycle
-virus cycle between humans & insect vectors
Describe the different host & vectors in arboviruses.
- Amplifying host
-level of virus can become high enough that an insect vector like a mosquito that feeds on it will prob become infectious - Dead end host or incidental host
-host from which inf agents aren’t transmitted to other sus hosts
-develop sufficient viremia to be picked up by insect vectors - Bridge vector
-arthropod that acquires virus from inf wild animal & transmits agent to human or secondary host
Describe common vehicle transmission.
-fecal contamination of food & water supplies (fecal-oral)
-virus contaminated meat or bone products
Describe iatrogenic transmission.
inf transferred during medical or surgical practice
1. Intro of pathogens by contaminated instruments (non sterile) or contaminated body surface
>ex: spread of equine inf anemia virus via multiple use syringe & needles
2. Intro of pathogen thru contaminated prophylactic or therapeutic preparations
Describe nosocomial transmission.
-while animal is in vet clinic
-hospital acquired infection
Describe vertical transmission.
-inf that is transferred from dam to embryo or fetus or newborn before, during, or shortly after partition
-EX: colostrum, milk, fecal contamination of teats
