lecture 11 Flashcards
virus epidemiology
-study of determinants, frequency, dynamics, and distribution of viral disease in populations
why study epidemiology in viral diseases
- risk of infection/disease in animal or animal population is determined by:
- -characteristics of virus (genetic variation from evolution)
- -host and host population (passive, innate, and acquired resistance)
- -behavioral, environmental, and ecological factors that affect virus transmission from one host to another
role of epidemiology in viral diseases
- identify/clarify role of viruses in etiology of diseases
- understand interaction of viruses with environmental determinants of disease
- determining factors affecting host susceptibility
- unraveling modes of viral disease transmission
- studying impacts of viral disease on health, economy, and society
- studying role of infectious pathogens in the pathogenesis of chronic non-communicable diseases such as oncogenic viruses in cancer
- large scale testing of vaccines and drugs (clinical trials)
how knowing epidemiology helps
- advance our understanding of nature of disease
- alerting and directing disease treatment, control, and prevention activities
- providing early warning systems and tracking disease
- assessment of economic and social impacts of disease
- assessment of efficacy and cost of disease control and prevention programs
case fatality rate
- based on outcome of disease in population
- number (%) of deaths among clinically ill animals
mortality rate
- based on outcome of disease in population
- number (%) of animals in a population that die from a specific disease over a specific period of time
morbidity rate
- based on outcome of disease in population
- percentage of animals in a population that develop clinical signs attributable to a particular virus over a defined period of time (commonly the duration of an outbreak)
factors based on duration and/or frequency of occurrence
- incidence
- prevalence
incidence
-number of new cases that occur in a population over a specified period of time
=number of cases x10^n/population at risk in a specified period of time
-measure of occurrence of infection or disease in a population over time
-especially useful for describing diseases of short duration
prevalence
-number of occurrences of disease (old and new cases), infection, or related attributes (antibodies) in a population, at a particular point in time
=number of casesx10^n/population at risk
-at a particular time
sporadic viral disease
-occurring occasionally, singly, or in scattered instances, and in a irregular or haphazard manner
enzootic viral diseases (endemic in humans)
-constant present 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 the 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 a large proportion of the population
asymptomatic carrier
- animals that have contracted an infectious viral disease but display no clinical symptoms
- shed virus, transmit disease to others
- shedding of virus may be continuous or intermittent
contagious disease
-disease spread from one person or organism to another by direct or indirect contact
period of contagiousness
-refers to time during which an infected animal sheds virus
exotic disease
-disease not known to occur in a particular country or geographical area
serioepidemiolgy
-simply denotes use of serological data as the basis of epidemiological investigation, as determined by diagnostic serological techniques
molecular epidemiology of viruses
-use of molecular biological data as the basis of epidemiological investigation of viral diseases
horizontal transmission of viruses
- contact transmission
- vector transmission
- vehicle borne transmission
- iatrogenic transmission
- nosocomial infection
horizontal transmission
- spread of infectious agent from one person/animal or group to another person/animal or group
- most viruses transmitted this way
contact (horizontal) transmission
-spread of infectious agent by direct or indirect (intermediate object) transmission
direct (horizontal)-
contact virus transmission
- involves actual physical contact between infected animal and susceptible animal (licking, rubbing, biting) also includes sexual contact
- droplet transmission: transmission of virus in droplet nuclei (saliva or mucus) that travels less than one meter to source of susceptible host
indirect (horizontal) contact transmission
-occurs via fomites (inanimate object/substance contaminated with infectious agent and capable of transmitting it), such as shared eating containers, bedding, dander, restraint devices, vehicles, clothing, improperly sterilized surgical equipment, or improperly sterilized syringes/needles
indirect-contact (horizontal) transmission- airborne
-spread of infectious agents by droplet nuclei in dust that travels more than one meter, sometimes for miles, from the infected to susceptible host
vector transmission
- can be mechanical or biological transmission
- arthropods can carry virus
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 mosquitoes and ticks
types of transmission cycles
- enzootic cycle (sylvatic or jungle cycle)
- epizootic cycle (rural cycle)
- urban cycle
enzootic cycle (sylvatic or jungle cycle)
natural transmission of virus between wild animals/birds (vertebrate hosts) and primary insect vectors
epizootic cycle (rural cycle)
-virus transmitted between non-wild or domestic animals and the primary or accessory insect vectors
urban 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
- they do not develop sufficient viremia to be picked up by insect vectors
common-vehicle transmission
includes fecal contamination of food and water supples (fecal-oral transmission) and virus-contaminated meat or bone products
-can contaminate meat or meat products
iatrogenic transmission
- infection transferred during medical or surgical practice
- can happen by: introduction of pathogens by contaminated instruments (non-sterile surgical instruments, syringes) or contaminated body surface (inadequate handwashing)
- example: spread of equine infectious anemia virus via multiple-use syringes and needles
- introduction of pathogen through contaminated prophylactic or therapeutic preparations
nosocomial transmission
- occurs when 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 or fetus, or newborn before, during, or shortly after parturition (colostrum, milk, or fecal contamination of teats)
zoonosis
used to describe infections that are transmissible from animals to humans
example of physical stability of a virus
-viruses that are transmitted by the respiratory route have low environmental stability, whereas those transmitted by fecal-oral route have higher stability
herd immunity
-form of immunity that occurs when the vaccination of a significant large portion of a population (or herd) provides a measure of protection for individuals who have not developed immunity
incubation period
- interval between infection and the onset of clinical signs
- in many diseases there is a period during which animals are infectious before they become sick
predromal period
- first signs and feelings of illness after incubation period
- period of early symptoms of disease occurring after the incubation period and just before the appearance of the characteristic symptoms of the disease
acute period
- when disease is at its height
- severe clinical signs
decline period
-period when clinical signs begin to subside
convalescent period
the body gradually returns to pre-diseased state and health is restored
