Epidemiology and Diagnosis of Viral Disease Flashcards
What is epidemiology?
study of the distribution and determinants of health-related states among specified populations and the application of that study to the control of health problems
There are many zoonotic viruses around the world. What seems to be the overall similarity between them?
most are RNA viruses
What is the One Health concept?
collaborative effects of multiple disciplines working locally, nationally, and globally to attain optimal health for people, animals, and the environment
What is the chain of infection?
causative agent —> reservoir —> portal of exit —> mode of transmission —> portal of entry —> susceptible host
What are the 4 steps to the generalized viral life cycle?
- execration from infected animal
- transfer to susceptible host
- replication within host
- execration from new host
What is the epidemiological triad
- AGENT: infectivity, pathogenicity, virulence, immunogenicity, antigenic stability, survival, dose
- HOST: species, age, sex, breed, conformation, genotype, nutritional status, physiologic condition, pathologic (immune) status, vaccination status, reproductive status
- ENVIRONMENT: weather/climate, season, housing, geography, geology, management, noise, air quality, food, chemical, ammonia concentration, water activity, UV light, organic matter
all contribute to disease potential
What are the 4 objectives of studying viral epidemiology?
- identify the causative agent of viral disease and relevant risk factors
- assess the severity of viral disease appearing in certain animal/human populations
- study the natural history and outcomes of viral disease of interest
- evaluate the efficacy and potency of some preventative and therapeutic strategies against viral diseases
What is epidemiology used to do concerning viral diseases?
- study the cause (etiology) of diseases, conditions, disorders, etc.
- determine the primary agent responsible for some viral diseases
- determine the characteristics of the viral disease and other causative factors
- determine the mode of transmission of viral diseases
- determine contributing factors to viral infection
- identify and determine geographic patterns of the viral disease
What is the iceberg concept of diseases?
a disease in which, for every visibly affected individual, the population will contain numerous others that are sub-clinically infected, carriers or undiagnosed clinical cases
What is the difference between endemic, epidemic, and pandemic?
ENDEMIC: enzootic; presence of several or continuous chains of transmission resulting in continuous occurrence of diseases in a population over a period of time
EPIDEMIC: epizootic; peaks in disease incidences which exceed the endemic baseline or expected incidences of diseases
PANDEMIC: panzootic; very extensive worldwide epidemic
What is an incubation period?
time intervals between the infection and the appearance of the clinical signs on the affected host
What is sero-epidemiology? Molecular epidemiology?
SERO: using serological (antibodies, antigens) data as a basis for epidemiology investigations
MOLECULAR: using molecular (DNA, RNA) data as a basis for epidemiology investigations
What is the difference between morbidity and mortality rates?
MORBIDITY: percentage of animals in population that develop clinical signs out of the total population (infection rate)
MORTALITY: percentage of dead animals from viral infection in relation to the total number of the population
What are the 2 branches of epidemiology?
- DESCRIPTIVE: studies that generate hypotheses and answer who, what, when, where (person/animal, place, time)
- ANALYTICAL: studies that test out hypotheses and generate conclusions on the particular disease to answer why and how (identified cause of viral disease/outbreak)
What personnel make up the epidemiology surveillance cycle?
- public and healthcare providers: clinicians, labs, hospitals, vets report to……
- health health department, which gives back feedback
What is the epidemic curve of an outbreak?
shows the number of illnesses in an outbreak over time; generally show the frequency of new cases compared to the date of disease onset
What are the 2 aims of the epidemiological surveillance in viral disease?
- discovery and control of transmission of viral infectious diseases
- develop prevention and control programs for viral infectious diseases
What are the 3 types of public health surveillance?
- ACTIVE: local or state health departments initiate the collection of information from labs, physicians, health care providers, or the general population (more complete and accurate)
- PASSIVE: labs, physicians, or other regularly report cases of disease or death to the local or state health department (doctor’s office reports measles cases, nursing home reports unusual numbers of patients with unexplained rashes)
- SYNDROMIC: ongoing, systematic collection, analysis, interpretation, and application of real-time indicators for disease that allow for detection before public health authorities might otherwise identify them (hospital admittance records)
What are the 4 types of epidemiologic investigations?
- case-control (retrospective): investigation starts after the disease episode starts
- cohort (prospective/longitudinal): investigations start with a presumed disease episode
- cross-sectional: cause of a specific disease is known
- long-term herd: provides information about presence and continued activity of virus in a given area
What are case-control studies used to investigate? What is the major benefit to this type of study? What must carefully be picked out? What is the focus of this study?
(retrospective)
- identify the cause ot disease outbreak
- uses existing data and is less expensive
- selection of the control groups to match the subject group
- individual animals or aggregates (herd/flock)
What are the 2 major requirements to cohort studies? What is a major drawback? Benefit?
(prospective/longitudinal)
1. creation of new data and records
2. careful selection of control group to be as similar to the exposed group with absence of any contact with the causative agent
- expensive due to long term follow-ups until disease is detected in a population
- proof of cause-effect relationship is very strong
What are the 2 major advantages to cross-sectional studies?
- can be carried out relatively quickly by the serology or virus identification
- provides data on the prevalence of virus infection in a population in a specific area
What study is used to produce data on the efficacy of viral vaccines and drugs?
long-term herd studies
What are the 3 sources of viruses?
- CLINICAL CASES: excretion of viruses may occur before the onset of clinical signs (FMDV in milk)
- CARRIER: animals are infected, but do not show clinical signs
- ANIMAL PRODUCTS: contaminated milk and meat; animal sera and vaccine can be contaminated with exogenous virus
What are the 6 major routes of virus shedding?
- ORAL: can be excreted in saliva
- FECAL: enteric viruses
- MILK: viremia
- SKIN: scabs, feather follicles
- UROGENITAL: urine, genital secretions
- RESPIRATORY: coughing, sneezing, halation from nose and mouth
How does particle size contribute to virus spreading?
> 100 μm fall out of suspensions and contaminate the environment
smaller particles are rapidly dehydrated to form droplet nuclei of 10 μm or less, which remain airborne and are able to be inhaled by susceptible animals
What are the main 2 categories of the mode of viral disease transmission?
- DIRECT: direct contact, droplet spread
- INDIRECT: airborne, vehicle (feed truck, boots), vector borne (mechanical [wings, legs], biological [bites, suckers])
(horizontal transfer)
What are the main 2 modes of viral disease transmission?
- DIRECT: direct contact, droplet spread
- INDIRECT: airborne, vehicle-borne (feed truck, boots), vector-borne (mechanical vs biological)
What is the difference between mechanical and biological vectors?
MECHANICAL: no viral replication in vector
BIOLOGICAL: virus replicates in arthropod vector
How can viral disease be vertically transmitted?
from parent to offspring
- in germ plasma
- through placenta
- through milk
- through egg
What are 5 common epidemiological-based antiviral control strategies?
- quarantine procedures
- sanitation procedures
- wildlife control
- vector control
- vaccines
In what 4 ways are quarantine procedures carried out?
- prohibition/restrictions of livestock or animals imports from certain areas where exotic diseases spread
- separation and testing of imported livestock at the portal of entry before they join the herd
- restriction of animal movement during epidemics
- keep closed herd strategies
What are 5 common ways that viruses are inactivated?
- HEAT: deleterious effects (low temp = preservation)
- UV IRRADIATION
- IONIZING IRRADIATION: gamma rays
- pH EXTREMES: less than 4 and greater than 9
- DESSICATION: drying/dehydration
What are 7 common chemicals used for viral disinfection?
- chlorine/iodine: hypochlorite is cheap, but rapidly inactivated by organic matter; iodophores are more stable, less corrosive, and more expensive
- formaldehyde: reliable, but hazardous due to toxicity
- phenolic compounds: not reliable for enveloped viruses
- caustic soda: effective, inexpensive, corrosive
- detergents: only effective against enveloped viruses
- chlorohexidine hibitane: unreliable against non-enveloped viruses
- 70% alcohol
What is the objective to sanitation procedures? What are 3 common procedures?
reduce the spread of viral infections
- slaughter, then safe disposal of carcases by incineration or burial of infected animal
- hygienic disposal of foodstuffs, bedding, and animal manure
- disinfection of buildings and surfaces
What is the objective to wildlife control? What are 3 common procedures?
restrict the sources of infection by reducing the exposure of domestic animals to the reservoir hosts
- keeping livestock in barns
- fencing pastures
- destruction/vaccination of wildlife
What is the objective to vector control? What are 3 common procedures?
reduce the potential risk of spread by insects
- apply insect-proofing in barns
- dipping or spraying animals with appropriate inesticides to control ticks, fleas, and lice
- environmental spraying with larvicides to control mosquitoes
What are notifiable diseases?
viral diseases that veterinarians have to report the prevalence of to local authorities, like the World Organization for Animal Health (OIE), who may notify neighboring countries
What are the main 3 sources of surveillance data?
- notifiable disease reports
- laboratory-based surveillance
- population-based surveillance
How is the investigation of viral diseases described?
discovery-to-control continuum
What are the 3 phases of the discovery-to-control continuum of viral disease investigation?
- EARLY PHASE: identify major parameters of epizootic potential, like mortality rates, severity, and transmissibility (discovery of new diseases, epidemiologic field investigation, etiologic investigation, diagnostic development
- INTERMEDIATE PHASE: expansion of many elements, focusing on research about etiology (vector biology, zoonosis), training, outreach, and education (risk communication, technology transfer, commercialization)
- LATE PHASE: animal health development and clinica; systems (public infrastructure, international agencies involvement)
What are the 9 steps of viral disease outbreak investigation?
- confirm occurrence of viral disease outbreak
- identification of viral causative agent
- build up a case definition and how to identify those cases
- describe epidemic (time, place, animal)
- build up and test hypothesis
- conduct environmental and epidemiological studies
- conclusion
- suggest appropriate control measures
- distribute recommendations to stockholders
What are the 4 common zones produced during quarantining of affected animals?
- INFECTED ZONE: minimum 3 km radius of infected premises
- BUFFER ZONE: area between 3 km and 10 km of the infected premises
- CONTROL ZONE: infected and buffer zones
- SURVEILLANCE ZONE: at least 10 km or wider outside of control zone
What are 6 recommended measures for the control of HPAI on the farm level?
- keep poultry away from areas frequented by wild fowl
- keep control over poultry houses by people and equipment
- maintain sanitation of property, poultry houses, and equipment
- appropriate disposal of manure and dead poultry
- stamping out, or culling, to eradicate disease
- appropriate disposal of carcases and all animals either by burial or incineration (carcases buried and overlaid with lime stone = environmental concerns)
