Epidemiology of Viral Diseases Flashcards
Epizootic Cycle (Rural Cycle)
Virus transmitted between non-wild or domestic animals and the primary or accessory insect vectors
Case Fatality Rate
Number (%) of animals in a population that die from a particular disease over a specific period of time
Droplet Transmission
Transmission of virus in droplet nuclei that travel less than one meter from the source to susceptible host
Ways in which Iatrogenic infection can occur
Introduction of pathogens by contaminated instruments or contaminated body surface
Introduction of pathogen through contaminated prophylactic or therapeutic practices
Incubation Period
Interval between infection and the onset of clinical signs
Overwintering
Survival of the virus from one ‘vector season’ to the next (period during which arthropods hibernate)
Incidence Rate (Attack Rate)
Meaure of the occurrence of infection or disease in a population over time
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
Virus Epidemiology
Study of determinants, freqency, dynamics and distribution of viral diseases in populations
Enzootic Cycle (Sylvatic or Jungle Cycle)
Natural transmissioin of virus between wild animals/birds and primary insect vectors
Iatrogenic transmission
Infection that is transferred during medical or surgical practice
Mechanical Transmission
Passive transport of the infectious agent on the feet or other body parts of the vector
Vertical Transmission
Usually used to describe infection that is transferred from dam to embryo/fetus/newborn, before/during/shortly after parturition
Seroepidemiology
Use of serological data as the basis of epidemiological investigation, as determined by diagnostic serological techniques
Amplifying Host
Level of virus can become high enough that an insect vector that feeds on it will probably become infectious
Airborne Transmission
Spread of infectious agents by droplet nuclei in dust that travel more than one meter, sometimes miles from the infected to susceptible host
Mechanism of Biological Transmission
- Arthropod vector acquires virus by feeding on blood of viremic animal
- Replication of ingested virus in gut then spread to salivary gland
- Virions in salivary secretions of vector are injected into new animal during blood meal
Mechanisms for overwintering
Transovarial Transmission
Trans-stadial Transmission
Main categories of disease determinants
Environmental Factors
Virus Factors
Host Factors
Trans-stadial Transmission
Virus is transmitted from larva or nymph to next stage of development (nymph or adult), but not transmitted vertically (from mother tick to eggs and next generation)
Enzootic Viral Diseases
Constant presence of a viral disease within a given geographic area
Extrinsic Incubation Period
Period from when virus is ingested by an arthropod vector and replication occurs in the gut to spread into the salivary glands.
Contagious Disease
Disease that is spread from one person or organism to another by direct or indirect contact
Inapparent Carriers
Carrier state may exist in an animal with an infection that is inapparent throughout its course
Nosocomial Infection
Occur while an animal is in a veterinary hospital or clinic
Vehicle Borne Transmission
Includes fecal contamination of food and water supplies and virus contaminated meat or bone products
Outcome of molecular epidemiology
General prevalence, information on genetic diversity and origin of viruses
Surveillance
Systemic collection, analysis, interpretation and dissemination of health data on an ongoing basis to gain knowledge of the pattern of disease occurrence and potential in a community in order to control and prevent disease.
Bridge Vector
Arthropod vector that acquires virus from an infected wild animal and subsequently transmits the agent to human or secondary host
Transovarial Transmission
Virus transmitted from the mother tick through infected eggs to next generation of ticks
Epidemiology
interdiciplinary field of science that takes into consideration multiple factors to provide data on pattern, spread, occurrence and impact of viral disease in population and also on the potential of occurrence of a viral disease in a population
Exotic Disease
Disease not known to occur in a particular country or geographical area
Morbidity Rate
Percentage of animals in a population that develop clinical signs attributable to a particular virus over a defined period of time (commonly during an outbreak)
Convalescent (Chronic) Carriers
Animals that shed virus during recovery from disease
Transmission cycles of Arboviruses
Enzootic Cycle
Epizootic Cycle
Urban Cycle
Urban Cycle
Virus cycle between humans and insect vectors
Decline Period
Period when clinical signs begin to subside
Mechanisms of Survival of Viruses
Physical stability
Host population size
Host Range
Persistant Infection
Avoid exposure to external environment
Droplet transmission is an example of (direct/indirect) contact.
Direct
Prodromal Period
First signs and feelings of illness after incubation period. Period of early symptoms of disease occurring after incubation period and before the appearance of classical symptoms of disease
Acute Period
Disease is at its height, severe clinical signs
Types of carriers
Incubatory
Convalescent
Inapparent
Carrier
Animals that have contracted an infectious viral disease but display no clinical symptoms
Fomite
Inanimate object or substance that is contaminated with the infectious agent and is capable of transmitting infectious organisms from one individual to another
Zoonosis
Infections that are transmissible from animals to humans
Most viruses are transmitted by the (horizontal/vertical) route
Horizontal
Herd Immunity
Form of immunity that occurs when the vaccination of a significant portion of a population (herd) provides a measure of protection for individuals who have not developed immunity
Stages of a typical infectious disease process
Incubation Period
Prodromal Period
Acute Period
Decline Period
Convalescent Period
Types of vector transmission
Mechanical Transmission
Biological Transmission
Incidence
Number of new cases that occur in a population over a specified period of time
Period of Contagiousness
Refers to the time during which an infected animal sheds virus
Prevalence
Number of occurrences of disease (old and new cases), infection, or related attributes (antibodies) in a population, at a particular time
Vertical transmission of viruses may cause
Early embryonic death or abortion
Congenital Disease
Congenital Defects
Direct Contact
Involves actual physical contact between infected animal and susceptible animal
Epizootic Viral Disease
Occurrence of more cases of viral disease than expected in a given area or among a specific group of people/animals over a particular time
Vector Transmission
Arthropod vectors carry the viruses from the infected host to susceptible host
Incubatory (Acute) Carriers
Animals that shed virus during the incubation period of the disease
Methods to study epidemiology of viruses
Seroepidemiology
Molecular epidemiology
Arboviruses
Class of viruses transmitted to humans by arthropods
Sporadic Viral Disease
Viral diseases occurring occasionally, singly or in scattered instances and in an irregular and haphazard manner
Mortality Rate
Number (%) of animals in a population that die from a particular disease over a specified period of time
Horizontal Virus Transmission
Spread of an infectious agent from one person/animal/group to another person/animal/group
Correlation of epidemiological serological data with clinical observations makes it possible to determine the ratio of
Clinical to Subclinical Infections
Biological Transmission
Infectious agent undergoes either a necessary part of its life cycle or multiplication in the vector before transmission to susceptible host
Panzootic Viral Disease
Virus epidemic occurring over a very wide area (several countries or continents) affecting a large proportion of the population
Transmission of Wester Equine Encephalitis Virus (WEEV)
- Enzootic and epizoodic transmission cycles
- Maintained in enzootic cycle between passerine birds as reservoirs and its specific mosquito vector
- Domestic and wild birds considered important reservoir and epizootic amplifying hosts
Molecular Epidemiology of Viruses
Use of molecular biological data as the basis of epidemiological investigation of viral diseases
Reservoir
Habititat in which infectious agent normally lives, grows and multiplies
Types of Virus Transmission
Vertical
Horizontal
Convalescent Period
Body gradually returns to its pre-diseased state and health is restored
