Epidemiology and Diagnosis of Viral Disease

Question 1

What is epidemiology?

Answer 1

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

Question 2

There are many zoonotic viruses around the world. What seems to be the overall similarity between them?

Answer 2

most are RNA viruses

Question 3

What is the One Health concept?

Answer 3

collaborative effects of multiple disciplines working locally, nationally, and globally to attain optimal health for people, animals, and the environment

Question 4

What is the chain of infection?

Answer 4

causative agent —> reservoir —> portal of exit —> mode of transmission —> portal of entry —> susceptible host

Question 5

What are the 4 steps to the generalized viral life cycle?

Answer 5

1. execration from infected animal
2. transfer to susceptible host
3. replication within host
4. execration from new host

Question 6

What is the epidemiological triad

Answer 6

• 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

Question 7

What are the 4 objectives of studying viral epidemiology?

Answer 7

1. identify the causative agent of viral disease and relevant risk factors
2. assess the severity of viral disease appearing in certain animal/human populations
3. study the natural history and outcomes of viral disease of interest
4. evaluate the efficacy and potency of some preventative and therapeutic strategies against viral diseases

Question 8

What is epidemiology used to do concerning viral diseases?

Answer 8

• 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

Question 9

What is the iceberg concept of diseases?

Answer 9

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

Question 10

What is the difference between endemic, epidemic, and pandemic?

Answer 10

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

Question 11

What is an incubation period?

Answer 11

time intervals between the infection and the appearance of the clinical signs on the affected host

Question 12

What is sero-epidemiology? Molecular epidemiology?

Answer 12

SERO: using serological (antibodies, antigens) data as a basis for epidemiology investigations

MOLECULAR: using molecular (DNA, RNA) data as a basis for epidemiology investigations

Question 13

What is the difference between morbidity and mortality rates?

Answer 13

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

Question 14

What are the 2 branches of epidemiology?

Answer 14

1. DESCRIPTIVE: studies that generate hypotheses and answer who, what, when, where (person/animal, place, time)
2. ANALYTICAL: studies that test out hypotheses and generate conclusions on the particular disease to answer why and how (identified cause of viral disease/outbreak)

Question 15

What personnel make up the epidemiology surveillance cycle?

Answer 15

• public and healthcare providers: clinicians, labs, hospitals, vets report to……
• health health department, which gives back feedback

Question 16

What is the epidemic curve of an outbreak?

Answer 16

shows the number of illnesses in an outbreak over time; generally show the frequency of new cases compared to the date of disease onset

Question 17

What are the 2 aims of the epidemiological surveillance in viral disease?

Answer 17

1. discovery and control of transmission of viral infectious diseases
2. develop prevention and control programs for viral infectious diseases

Question 18

What are the 3 types of public health surveillance?

Answer 18

1. 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)
2. 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)
3. 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)

Question 19

What are the 4 types of epidemiologic investigations?

Answer 19

1. case-control (retrospective): investigation starts after the disease episode starts
2. cohort (prospective/longitudinal): investigations start with a presumed disease episode
3. cross-sectional: cause of a specific disease is known
4. long-term herd: provides information about presence and continued activity of virus in a given area

Question 20

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?

Answer 20

(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)

Question 21

What are the 2 major requirements to cohort studies? What is a major drawback? Benefit?

Answer 21

(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

Question 22

What are the 2 major advantages to cross-sectional studies?

Answer 22

1. can be carried out relatively quickly by the serology or virus identification
2. provides data on the prevalence of virus infection in a population in a specific area

Question 23

What study is used to produce data on the efficacy of viral vaccines and drugs?

Answer 23

long-term herd studies

Question 24

What are the 3 sources of viruses?

Answer 24

1. CLINICAL CASES: excretion of viruses may occur before the onset of clinical signs (FMDV in milk)
2. CARRIER: animals are infected, but do not show clinical signs
3. ANIMAL PRODUCTS: contaminated milk and meat; animal sera and vaccine can be contaminated with exogenous virus

Question 25

What are the 6 major routes of virus shedding?

Answer 25

1. ORAL: can be excreted in saliva 2. FECAL: enteric viruses 3. MILK: viremia 4. SKIN: scabs, feather follicles 5. UROGENITAL: urine, genital secretions 6. RESPIRATORY: coughing, sneezing, halation from nose and mouth

Question 26

How does particle size contribute to virus spreading?

Answer 26

> 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

Question 27

What are the main 2 categories of the mode of viral disease transmission?

Answer 27

1. DIRECT: direct contact, droplet spread 2. INDIRECT: airborne, vehicle (feed truck, boots), vector borne (mechanical [wings, legs], biological [bites, suckers]) (horizontal transfer)

Question 28

What are the main 2 modes of viral disease transmission?

Answer 28

1. DIRECT: direct contact, droplet spread 2. INDIRECT: airborne, vehicle-borne (feed truck, boots), vector-borne (mechanical vs biological)

Question 29

What is the difference between mechanical and biological vectors?

Answer 29

MECHANICAL: no viral replication in vector BIOLOGICAL: virus replicates in arthropod vector

Question 30

How can viral disease be vertically transmitted?

Answer 30

from parent to offspring - in germ plasma - through placenta - through milk - through egg

Question 31

What are 5 common epidemiological-based antiviral control strategies?

Answer 31

1. quarantine procedures 2. sanitation procedures 3. wildlife control 4. vector control 5. vaccines

Question 32

In what 4 ways are quarantine procedures carried out?

Answer 32

1. prohibition/restrictions of livestock or animals imports from certain areas where exotic diseases spread 2. separation and testing of imported livestock at the portal of entry before they join the herd 3. restriction of animal movement during epidemics 4. keep closed herd strategies

Question 33

What are 5 common ways that viruses are inactivated?

Answer 33

1. HEAT: deleterious effects (low temp = preservation) 2. UV IRRADIATION 3. IONIZING IRRADIATION: gamma rays 4. pH EXTREMES: less than 4 and greater than 9 5. DESSICATION: drying/dehydration

Question 34

What are 7 common chemicals used for viral disinfection?

Answer 34

1. chlorine/iodine: hypochlorite is cheap, but rapidly inactivated by organic matter; iodophores are more stable, less corrosive, and more expensive 2. formaldehyde: reliable, but hazardous due to toxicity 3. phenolic compounds: not reliable for enveloped viruses 4. caustic soda: effective, inexpensive, corrosive 5. detergents: only effective against enveloped viruses 6. chlorohexidine hibitane: unreliable against non-enveloped viruses 7. 70% alcohol

Question 35

What is the objective to sanitation procedures? What are 3 common procedures?

Answer 35

reduce the spread of viral infections 1. slaughter, then safe disposal of carcases by incineration or burial of infected animal 2. hygienic disposal of foodstuffs, bedding, and animal manure 3. disinfection of buildings and surfaces

Question 36

What is the objective to wildlife control? What are 3 common procedures?

Answer 36

restrict the sources of infection by reducing the exposure of domestic animals to the reservoir hosts 1. keeping livestock in barns 2. fencing pastures 3. destruction/vaccination of wildlife

Question 37

What is the objective to vector control? What are 3 common procedures?

Answer 37

reduce the potential risk of spread by insects 1. apply insect-proofing in barns 2. dipping or spraying animals with appropriate inesticides to control ticks, fleas, and lice 3. environmental spraying with larvicides to control mosquitoes

Question 38

What are notifiable diseases?

Answer 38

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

Question 39

What are the main 3 sources of surveillance data?

Answer 39

1. notifiable disease reports 2. laboratory-based surveillance 3. population-based surveillance

Question 40

How is the investigation of viral diseases described?

Answer 40

discovery-to-control continuum

Question 41

What are the 3 phases of the discovery-to-control continuum of viral disease investigation?

Answer 41

1. 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 2. INTERMEDIATE PHASE: expansion of many elements, focusing on research about etiology (vector biology, zoonosis), training, outreach, and education (risk communication, technology transfer, commercialization) 3. LATE PHASE: animal health development and clinica; systems (public infrastructure, international agencies involvement)

Question 42

What are the 9 steps of viral disease outbreak investigation?

Answer 42

1. confirm occurrence of viral disease outbreak 2. identification of viral causative agent 3. build up a case definition and how to identify those cases 4. describe epidemic (time, place, animal) 5. build up and test hypothesis 6. conduct environmental and epidemiological studies 7. conclusion 8. suggest appropriate control measures 9. distribute recommendations to stockholders

Question 43

What are the 4 common zones produced during quarantining of affected animals?

Answer 43

1. INFECTED ZONE: minimum 3 km radius of infected premises 2. BUFFER ZONE: area between 3 km and 10 km of the infected premises 3. CONTROL ZONE: infected and buffer zones 4. SURVEILLANCE ZONE: at least 10 km or wider outside of control zone

Question 44

What are 6 recommended measures for the control of HPAI on the farm level?

Answer 44

1. keep poultry away from areas frequented by wild fowl 2. keep control over poultry houses by people and equipment 3. maintain sanitation of property, poultry houses, and equipment 4. appropriate disposal of manure and dead poultry 5. stamping out, or culling, to eradicate disease 6. appropriate disposal of carcases and all animals either by burial or incineration (carcases buried and overlaid with lime stone = environmental concerns)