Epidemiology Exam 1

What are the five steps to implementing evidence based medicine?

1. Formulate the problem 2. Track down the best evidence 3. Appraise the evidence critically 4. Implement the results 5. Evaluate new performance

What are the seven steps to constructing an epidemic curve?

1. Identify the date of onset 2. Set time interval-1/3 or less of incubation period 3. Create x-axis lead and end periods(2 incubation periods) 4. Draw tick marks and label time intervals 5. Assign area equal to one case on the y-axis 6. Plot cases on the graph 7. Mark critical events and add labels

What are the four main elements of a good clinical question?

1. Patient/problem 2. Intervention 3. Comparison intervention(if appropriate) 4. Outcome

Define immunogenicity.

Ability of an agent to stimulate an immune response in the host. High immunogenicity is associated with fewer reoccurrences of disease in an individual.

Define viability.

Ability of an agent to withstand environmental stress.

What are the three criteria used to distinguish abnormal from normal?

Abnormal as unusual-distinction based on the distribution value of characteristics in the "normal" population. Eg. 2.5% lowest and highest values are considered abnormal. Abnormal as associated with disease-measurements are abnormal if they are regularly associated with disease. Eg. Blood glucose >120mg/dL is typically associated with diabetes. Abnormal as associated with response to therapy-measurement is considred abnormal if treatment of patients with equal or higher values leads to a better outcome.

What is the difference between accuracy and precision?

Accuracy-validity, the extent to which observations represent the truth. Precision-reliability, reproducibility, the extent to which repeated measures of the same factor are close together.

Actual distribution and normal distribution typically conform to a bell shaped curve. How does actual distribution typically differ from normal distribution?

Actual distribution will tend to be skewed toward one end, where the normal distribution is a perfect bell curve.

What are some possible types of animal patterns of disease?

Age, sex, species, breed, genetics, etc.

Susceptible host.

An animal that can be infected by an infectious agent.

What is a disease carrier?

An infected person or animal that sheds an agent in the absence of discernible clinical signs and serves as a potential source of infection.

Define antigenic stability.

Antigenic stability is the likelyhood that the antigenic structure of an agent will undergo mutation or change. Agents with high antigenic stability are easy to make vaccines for that have long lasting immune protection.

What is a determinant of health/disease?

Any factor that when changed, produces a change in disease frequency or disease characteristics.

Define reservoir of infection.

Any living or nonliving matter where an agent can live, multiply, maintain a population, and be transmitted to new hosts.

What is the difference between association of factors and interaction of factors?

Association of factors-factors that happen with disease but may or may not actually affect the disease(eg. carrying a lighter is associated with lung cancer, but does not cause it). Interaction of factors-determinants rarely act in isolation. There are almost always multiple factors that affect a disease.

Why are the reservoir and source of infect the same for most viruses?

Because viruses typically cannot survive for long periods of time outside of a susceptible host cell.

What is biological control of disease? What are some examples?

Biological control employs living organisms to combat disease. Eg. sterile males are introduced into a population of vectors to reduce the number of vectors in an area.

What is biosecurity?

Biosecurity is the use of management practices to reduce spread of infectious agents within food animal products.

What are the conditions under which a disease can be considered eradicated?

Both the clinical cases and causative pathogen must be eliminated so that there are no future cases. Disappearance of clinical cases that leave sub-clinical cases does not qualify as eradication.

What is a causation web?

Causation web is a method of conceptualizing and visualizing the interaction of multiple direct and indirect factors on a disease process.

What are central tendency and dispersion, and how are they used to summarize interval characteristics?

Central tendency-mean, median, and mode; express the average, middle, and most frequent measurements from a group of measurements. Dispersion-range, standard deviation, and percentile; express the lowest and highest measurements, the average difference between each value and the mean, and the proportion of all observations falling between specified values.

What five factors affect the rate of infectious disease in a population?

Characteristics of the infectious agent Individual host immunity of animals in the population Population structure Population dynamics Contact rate

What are the three categories of genetic diseases?

Chromosomal disorders mendelian disorders Multifactorial disorders

Differentiate between clinical trials and observation studies.

Clinical trials-researchers apply an intervention and study the results Observation studies-researcher only observes the events taking place, and has no direct interaction with test subjects.

What are the seven sub-disciplines of epidemiology?

Clinical, computational, genetic, field, participatory, molecular, and spatial/geographical

How do cohort studies differ from cross-sectional studies? What is a case-control design?

Cohort studies-follow subjects over time. Cross-sectional studies-make observations in a single point of time.

What are the two types of direct transmission?

Contact(contagious disease), and Coitus(venereal disease)

What are the four types of epidemiology?

Descriptive, Analytical, Experimental, and Theoretical

What are the three types of biological vector transmission?

Developmental transmission-essential development phase of an agent occurs in the vector. Propagative transmission-multiplication of the agent occurs in the vector. Cyclopropagative transmission-both development and multiplication occur in the vector.

Define disease control.

Disease control is the reduction of disease prevalence to a level that is no longer a major health/economic problem. The primary objective is to contain the disease by limiting or stopping its spread.

What is disease eradication? Is there such a thing as total eradication, or partial eradication? On what scale can the term eradication be applied to a disease?

Disease eradication is the total elimination of a disease due to the removal of its cause. Total eradication is redundant(see definition), and partial eradication is an oxymoron. Disease eradication can be on a global, national, or local scale. It is appropriate to say that a disease has been eradicated from a herd or facility.

Define sporadic occurence.

Disease occurs irregularly or haphazardly-small localized outbreaks.

How do species and breed affect disease processes?

Diseases may be limited to a specific species or group of species for host(eg. rabies-multiple host species, canine distemper-dogs only). Some breeds have become genetically predisposed or sensitive to certain diseases.

What are the three groups of chemical disease control?

Disinfectants-attempt to destroy agents on equipment or environment. Insecticides-reduce vectors in the environment or prevent vectors from attaching to the animal. Antimicrobials-prophylactic treatment, or given as treatment of already infected animals.

Define effective contact

Effective contact is the condition under which infection of a new host will occur. Eg. length of exposure, portal of exit, portal of entry, stability of the organism.

How does knowing the life cycle of an agent affect the selection of a control strategy?

Eg. Being able to eliminate a vector that is required for maturation of the agent prevents the spread of the agent. If one stage of the life cycle is more susceptible to a drug than another stage, the drug needs to be used during the appropriate stage.

How might geographical location change disease patterns?

Environmental pollutants can increase disease prevalence. Noise is a stressor that can decrease an animals health. Disease patterns can change by season in certain areas.

Define pandemic occurrence.

Epidemic on a scale which crosses international boundaries or becomes global. Involves large numbers of individuals.

Define Epidemiology

Epidemiology is the study of patterns of health and disease in populations and the factors that influence these patterns.

What are the three different methods by which a vector might reach a host?

Flying vectors-actively seek out host Non-flying vectors-rely on passive contact with host Water-inhabiting vectors-agent is released from the vector into water and passively disseminates

Why does research still go into new testing methods?

Gold standard test is typically invasive or expensive.

What are the 5 types of carriers?

Healthy or asymptomatic carriers Incubatory carriers Convalescent carriers Intermittent shedders Chronic carriers

What are the five types of vertical host transmission?

Hereditary Congenital During birth Colostrum Suckled milk

Under what circumstances is it best to use a specific test?

High penalty for false positives Useful to "rule in" disease *most useful when result is positive *often used as a follow up or confirmation test

Under what circumstances is it best to use a sensitive test?

High penalty for misdiagnosis/nondetection Early diagnositics, rule outs Tests with few false negatives *results are most useful when they are negative

How does the proportion of immune individuals relate to the level of herd immunity?

Higher numbers of immune individuals raises the level of herd immunity.

How does sex have an affect on disease?

Hormonal-sex hormones may change susceptibility to disease, pregnancy, parturition, and lactation may also increase susceptiblity. Behavioral-one sex may be more likely to engage in an activity which exposes the individual to disease(eg. fighting) Genetic differences-sex-linked(genetic on y chromosome), sex-limited(diseases involving the reproductive track), sex-influenced(lower disease threshold in one sex).

Reservoir host.

Host in which an agent lives and multiples. Synonymous with Primary host.

Definitive(final) host.

Host in which an agent undergoes its sexual phase of reproduction.

Paratenic host.

Host in which the agent is carried without undergoing any development before being passed to a new host. (acts as a mechanical vector).

Intermediate host.

Host in which the agent undergoes some development, usually asexual reproduction.

Amplifier host.

Host in which there is a sudden increase in the amount of agent due to an increase of host population. Eg. Infected female has a litter of offspring, and passes the agent to all of the offspring.

Incidental(dead-end or accidental) host.

Host that is incapable of transmitting an agent to another host.

Secondary(aberrant) host.

Host that is involved in the life-cycle of an agent outside the endemic area. May act as a maintenance host.

Primary(natural or maintenance) host.

Host that maintains infection in an endemic area. Agents depend on this host for long-term existence. Synonymous with Reservoir host.

Link host.

Host which links to other host species that otherwise would not have contact. Eg. marsh herons give Japanese encephalitis to pigs; and pigs pass it to humans.

Husbandry involves housing, nutrition, and management. Give some examples of how each of these can affect disease patterns.

Housing-proper ventilation, bedding and floor surfaces protect from macroclimates Nutrition-proper nutrition prolongs life and reduces disease effects Management-stock densities and replacement policy can limit or exacerbate disease spread and severity.

What is the primary source of water-borne ingestion of agents in humans? In animals?

Humans: municiple water Animals: surface water

What is the difference between hyperendemic, hypoendemic, and holoendemic?

Hyperendemic-high level affecting all age groups Hypoendemic-low level affecting all age groups Holoendemic-high level affecting the young, and low level affecting the adults

How does the portal of entry affect the incubation period of an agent?

If the portal of entry is close to the target tissue, incubation period will be shorter.

How does immunological status affect disease determinance? How is immunological protection gained?

Immune status can provide protection from contracting a disease or lessen the severity of a disease. Immune protection is gained from colostrum(dam to offspring), vaccination, or recovery from previous infection.

How does age affect disease processes?

Immunity to diseases is lower in the very young and very old, either allowing the disease to manifest in the first place, or manifesting in a more severe manner. Age can also have an effect on the side effects of some vaccinations.

What factors affect the shape of an epidemic curve?

Incubation period Infectivity of the agent Proportion of susceptible hosts in the population

Differentiate between incubation period and induction period.

Incubation period-interval between exposure to an infectious agent and onset of disease. Induction period-interval between exposure to a chemical agent and onset of disease.

Differentiate between infection, contamination, and pollution.

Infection-entry and multiplication of agent in the body. Contamination-presence of an agent on exterior surfaces of a body or object. Pollution-offensive matter in the environment that is not an infectious agent.

Define infectivity.

Infectivity is an agents ability to enter, multiply and produce change in a host. The change in the host can be anything from disease to immune response with no symptoms.

What are the three methods of food-borne ingestion transmission.

Ingestion of meat from infected animals Ingestion of contaminated food Predator chain transmission(subtype of eating infected animals)

How are host resistances modified at the innate and acquired levels?

Innate: selective breeding with disease resistant breeds. Acquired: vaccination, insuring ingestion of colostrum.

What is internal validity? External validity?

Internal validity-the degree to which a study design and conduct eliminates the possibility of bias. External validity-the extent to which the results of a study can be correctly applied to other circumstances.

What differentiates intrinsic and extrinsic determinants?

Intrinsic determinants are internal to the host(ie. age, breed, species, etc). Extrinsic determinants are external to the host(ie. trauma, poison, radiation, etc).

What are the six uses of epidemiology?

Investigation and control of a disease of unknown etiology Identification of the etiology & risk factors of a disease Determination of the origin of a disease of known etiology To study the natural history and prognosis of a disease Planning, monitoring & assessment of d'se control programs Assessment of the magnitude and impact of a disease

What six factors affect the communicability of an agent?

Length of communicability period-time in which an agent is shed from the host. Number of host species-increases the likelihood of finding a new susceptible host. Chance of exposure of susceptible hosts-herd immunity or method of transfer. Ease of exit-eg. respiratory disease vs. muscle infection Infective dose-number of agent particles required to produce disease. Viability of agent-ability of agent to survive outside the host.

What is a likelihood ratio? How is it determined for a positive test? A negative test?

Likelihood ratio expresses the likelihood that a given result will occur in an animal with, as opposed to without a disease. For a positive test the likelihood ratio is the true positive rate divided by the false positive rate(sensitivity/1-specificity). For a negative test the likelihood ratio is the false negative rate divided by the true negative rate(1-sensitivity/specificity).

What is macroclimate and how does it affect disease?

Macroclimate is the climate and weaterh conditions of a geographical area. Eg. Hurricanes, storms, and wind can carry infectious agenst over long distances. Extreme cold, extreme heat, and drought or excessive rain can all have an effect on disease prevalence as well.

What is the difference between a mechanical vector and a biological vector?

Mechanical-agent does not undergo any developmental changes while in the vector. Biological-agent undergoes some development while in the vector and requires the vector for that stage.

For the long-term survival of an infectious agent, which level of immunity(high, medium, or low) is best in an individual?

Medium individual immunity is best for long-term survival of an agent. It allows the agent to survive the brunt of the host reaction, without killing the host.

What is the difference between natural and strategic vaccination?

Natural vaccination is the building of immunity by direct exposure to the agent, or one that is antigenically cross reactive. Strategic vaccination is the administration of manufactured vaccine to an individual.

What are the three types of clinical measurement scales?

Nominal-categories with no ordered relationship to one another. Eg. breed, color, sick/well Ordinal-categories that have an ordered relationship to one another, but without specified or equal intervals. Eg. Grade of heart murmur, or hip dysplasia. Interval-categories have an ordered relationship to one another with a defined interval between each measurement. Can be continuous(expressed as a decimal), eg. weight; or discrete(whole numbers), eg. heart rate, WBC count.

What potential biases should you look for in a test study?

Not running the gold standard test on all patients(does not diff. between true neg. and false neg.) Test results are interpreted using the gold standard test results(may make the new test look better than it is)

Which measurement scales must have a cutoff point between normal and abnormal?

Ordinal and interval.

What is positive predictive value? How is it calculated?

PPV is the probability that a positive test result is actually positive. PPV=True positive/(True pos. + False pos.)

What is parallel testing? When is it most often used?

Parallel testing is the use of multiple tests in which any positive result makes the individual positive for disease. This increases sensitivity and the negative predictive value, and should be used when missing the diagnosis is detrimental, or the treatment of false positive animals is not dangerous.

Differentiate between pathogenicity and virulence.

Pathogenicity is the ability of an agent to produce clinical disease. Virulence is the degree of pathogenicity or severity of the disease caused.

What are the three types of disease determinants? Give an example of each.

Physical-natural disasters Biological-gender, sex, genetic predisposition Behavioral-hand washing

What are the differences between point source epidemics and propagated epidemics?

Point source-all affected get sick at the same time from a single source, and outbreak lasts for a very short time. Approaches symmetry at average incubation period. Propagated-starts slowly over a long period, then quickly rises(similar to logorithmic), may start with a single or multiple sources. Tendency to plateau, but secondary peaks may occur as a result of movement into or out of the population. Incubation period is the time between primary and secondary cases.

What is post-test likelihood synonymous with, and how is it determined?

Post-test likelihood is the likelihood of disease given a positive or negative result. Pretest odds X likelihood ratio = post-test odds.

What differentiates primary and secondary determinants?

Primary determinants have major effects on the individual or population (ie. the disease causing agent). Secondary determinants predispose or enable the disease to spread(ie. poor hygiene).

What is the difference between a primary vehicle of transmission and a secondary vehicle?

Primary vehicles are excretions, fluids or tissues from the body of the transmitting host. Secondary vehicles are inanimate objects that have been contaminated with primary vehicles.

Give an example of how population structure affects disease spread.

Proportion of immune and susceptible animals in the population. The presence of alternative hosts or vectors near/in the population.

Differentiate between prospective studies, retrospective studies, and case-control studies.

Prospective studies-Begin in the present and follow subjects into the future Retrospective studies-examine information collected in the past. Case-control studies-compare a group of diseased animals with a group of animals without that disease.

What is the difference between quarantine and isolation?

Quarantine is the separation of a group irregardless of disease status, to stop spread out of that group. Isolation is the separation of a group or individuals that are confirmed to have the disease, to prevent transmission to other susceptible members.

What is the purpose of a ROC curve?

ROC curve is the plot of sensitivity vs. the inverse of specificity(1-sp), with a non informative line(1:1 ratio, se:1-sp). The curve indicates the best cut off point as the point on the curve that is closest to the 100:0 point. If the plots of se vs. sp lie very close to the non informative line, the test is probably not worth using.

How does changing the cut of point for normal vs. abnormal change the sensitivity and specificity of the test? What point is best used as a cut off?

Raising the cut off point will increase sensitivity, but increases the risk of false negatives. Lowering the cut off point will increase specificity, but increases the number of false positives. The best cut off point is the point at which non diseased individuals and diseased individuals have the least amount of overlap in parameters.

Differentiate between random sampling and convenience sampling.

Random sampling-random sample of individuals is drawn from a population. Convenience sample-subjects that meet the entry criteria and are easily accessible to the investigator.

What are the two types of spatial patterns?

Random spacial: sporadic outbreaks in different locations Clustering spatial: aggregation of outbreaks in amounts greater than predicted by chance.

Give an example of how population dynamics affect disease spread.

Rate of movement in and out of the population Social distance(how close do animals stand, territory size) Behavior(shared grooming, fighting, etc)

How are rate, ratio, and proportion used to summarize nominal or ordinal characteristics?

Ratio-compares the number of individuals in two different groups with no element of time. Eg. 10 males/2 females with colic equals a ratio of 5:1. Proportion-compares the number of individuals in a group to all individuals, with no element of time. Eg. 5 diseased animals/100 total animals equals 1/20, or 5%. Rate-a proportion with the added element of time. Eg. 5 diseased animals/100 total animals per month.

What is regression to the mean, and how does it validate retesting patients with only moderately abnormal values?

Repeated testing on patients selected for extreme values will tend to yield values closer to the mean if the animal is not diseased. By repeating the test, you can better distinguish between a single fluctuation outside of normal range, and a patient that is actually diseased.

What are the six portals of exit that an agent may use to exit a host?

Respiratory tract Alimentary tract Urinogenital tract Eyes Body surfaces Mixed

Differentiate between ring vaccination, barrier vaccination, and suppressive vaccination.

Ring: all populations surrounding an infected population are vaccinated to prevent spread out of the original group of susceptibles. Barrier: all populations across a certain line are vaccinated to prevent spread across that line. Works best in areas that are limited on either side by geographical barriers(eg. water). Suppressive: similar to ring vaccination, except that all individuals in the original group are vaccinated as well.

What are selection bias, observational bias, and confounding bias?

Selection bias-patients in treatment group differ from the control group in a way that influences outcome. Observational bias-measurement of outcome is systematically different between groups Confounding bias-an unknown factor is related with the risk factor and the outcome.

What is the difference between selective slaughter and complete depopulation? Under which circumstances would each be called for?

Selective slaughter: individuals are tested, and the positive animals are culled. This is an acceptable practice with low risk, or slow spreading diseases. Complete depopulation: an entire herd or population is culled when any member of the population is confirmed with a disease. This is called for in rapidly spreading diseases or those with serious consequences, and is often used in eradication programs.

What is test sensitivity? How is it calculated?

Sensitivity is the ability of a test to detect disease. Se=True positive/(True pos. + False neg.)

What is serial testing? When is it most often used?

Serial testing is the use of multiple tests in which any negative result makes the individual negative for disease, and all results must be positive for a positive diagnosis. Serial testing maximizes specificity and positive predictive value, and should be used when false positives are detrimental, or missing the diagnosis is not critical.

What are the three types of temporal patterns of disease?

Short-term: typical epidemics Cyclical: periodic fluctuations of disease occurance Secular: long term increases or decreases in disease rates

What spectrum of subjects should you look for in a test study?

Similar to patients in your practice(species, breed, etc) Non-diseased animals should have similar signs to diseased animals, as opposed to being normal healthy animals-test may react differently to normal animals vs. those sick with a different disease.

How might size and conformation affect disease processes?

Size: eg. large dogs are prone to hip displasia because of increased weight load. Conformation: eg. cows with small pelvic outlet relative to size are prone to dystocia.

What are the eight methods of disease control?

Slaughter Quarantine Reduction of contact Chemical use Modification of host resistance Environmental and/or management control Education Biological control

What circumstance increases the effect of chance events on a test study?

Small sample size. Larger sample sizes will have a better confidence interval.

Give an example of how spatial and temporal separation serve to reduce contact between infected and susceptible individuals.

Spatial: separate holding barns for neonates or young may prevent sub-clinical adults from infecting the young. Temporal: Managing herds with an all-in-all-out method prevents new animals from introducing disease into an established population and gives time between populations for the environment to be cleaned and disinfected.

What is test specificity? How is it calculated?

Specificity is the ability of a test to detect the lack of disease. Sp=True negative/(True neg. + False pos.)

What are the three factors that influence the predictive value of a test?

Specificity, sensitivity, and pre-test prevalence of disease. **Prevalence is not just prevalence of disease among individuals of a host group, but individuals with similar presenting history as the patient in question. Eg. prevalence of Felv in healthy cats, vs. cats that have begun to show disease symptoms.

Give an example of social or ethological effects on disease.

Tail biting in pigs-infected wounds Rolling behavior in horses-gastric torsion Livestock learn to avoid poisonous plants in their local environment but do not know to avoid poisonous plants not native to the area.

What are three examples of microclimate? How do they effect diseases?

Terrestrial-surface of leaves, affects the development of vectors and parasites. Biological-on the animal's body, may effect the spread of a disease process in the host. Larger microclimates such as pens, kennels, etc-poor hygiene and environmental management can increase disease spread between individuals and severity of disease.

What is the purpose of experimental epidemiology?

Tests hypotheses formulated by descriptive and analytical epidemiology about disease patterns.

What is the epidemiologic triad?

The combination of host, agent, and environmental determinants.

Define communicability. What are synonyms for communicability?

The ease and speed with which an agent is transmitted in a population of susceptible individuals. Synonyms: transmissibility and infectiousness. *Contagiousness refers to communicability of agents spread by direct contact.*

What has to be known about a population before an epidemic can be recognized?

The endemic level of disease in the population.

What is the goal of primary prevention? What stage of infection does it interrupt?

The goal of primary prevention is to reduce the incidence of disease. This may be accomplished either by preventing exposure to causal factors, or by preventing the pathologic process after exposure.

What is the goal of secondary prevention? What stage of infection does it interrupt?

The goal of secondary prevention is to reduce the prevalence of disease in a population by shortening its duration. This relies on early detection and treatment of disease, and removal of individuals that can serve as a source of infection to others.

What is the goal of tertiary prevention? What stage of infection does it interrupt?

The goal of tertiary prevention is to reduce the number or impact of disease consequences. This is accomplished by appropriate treatment after clinical signs have appeared.

Define infectious dose.

The infectious dose is the quantity of an agent necessary for transmission and infection from one host to the next.

What is space-time clustering?

The interaction between place and time of disease occurrence. This is an epidemic!

Define epidemic occurence.

The occurrence of disease at a level in excess of the expected. *a single occurrence in an population that expects 0% infection is technically an epidemic!

Define contact rate.

The rate at which susceptibles interact with infected animals.

Define random variation and bias. How does each affect accuracy and precision?

Variation-error that occurs to the same extent in both directions from the true value. Affects precision but not accuracy. Bias-error that occurs only in one direction from the true value. Affects accuracy but not precision.

Provide an example of how environmental and management control can prevent the spread of disease.

Washing and drying teats before milking prevents mastitis. Adequate ventilation in indoor facilities may prevent the spread of airborne diseases.

What are the four types of airborne transmission?

Dust-requires highly viable agents Expiratory droplets-typically associated with URI Droplet nuclei-small particles spread over long distances Vapors and gases-agent is typically chemical in nature, presents similar to direct transmission.

What is negative predictive value? How is it calculated?

NPV is the probability that a negative test result is actually negative. NPV=True negative/(True neg. + False neg.)

Epidemiology involves describing the patterns of disease in relation to what three factors?

individuals, place, and time

What differentiates a source of infection from a reservoir of infection?

A source of infection is only the matter from which an agent was transmitted to a susceptible host. The agent does not have to be maintained in the source of infection.

Define vehicle or fomite.

Inanimate objects contaminated with infectious agents

What two factors determine the servival of an infectious agent?

Successful transmission and maintenance of the life-cycle.

What is extrinsic incubation period?

The time required for development of an agent in a vector, from infection of the vector to the point when the vector is no longer able to transmit the agent.

Define endemic occurrence.

The usual frequency of disease occurrence in a population, or the constant presence of a disease in a population.

How does host range of an agent act as a determinant of disease?

The wider an agent's host range is, the better the survival of the agent. A narrower host range makes an infectious agent easier to control.

What is iatrogenic transmission?

Transmission of an agent during surgical or medical procedures.

Differentiate between transovarian transmission and transstadial transmission.

Transovarian-transmission of agent from female to ova of a vector. Transstadial-transmission of agent from one life stage to another in a vector.

When comparing test results with a patients disease status, what are the four possible outcomes?

True positive-pos. test, with disease False positive-pos. test, without disease True negative-neg. test, without disease False negative-neg. test, with disease

What are the four types of indirect transmission?

Vehicles/fomites Airborne Ingestion Vectors

Give an example of how occupation may increase the occurrence of disease.

Veterinarians have a higher risk of zoonotic diseases because they work with a variety of animals on a frequent basis.

How might coat color change the effect of a disease?

White cats lack protective pigments in the skin that make them more susceptible to cutaneous squamous cell carcinoma.

What questions does descriptive epidemiology answer?

Who, what, where, and when.

What questions does analytical epidemiology answer?

Why and how.

Can herd immunity be induced without inducing host immunity?

Yes. By limiting the contact of susceptible individuals with other susceptibles, disease spread can be prevented. *think quarantine*

What is an epidemic curve?

A curve delineating the progression and regression of new cases in an outbreak.

What is the purpose of a diagnostic test? What are some examples?

A diagnostic test helps to predict the likelyhood or presence of disease. Examples: Lab test, history, PE findings

Define prophylactic prevention.

A form of prevention which involves medical and sanitary components.

What is a gold standard test? What are some examples?

A gold standard test is one which most accurately classifies patient status. Eg. certain lab tests, biopsy, necropsy, or culture.

Define host.

A host is an organism that is capable of being infected by an infections agent. Replication and development usually occur within the host.

What is a Nidus?

A nidus is a center where infection settles and spreads from. Eg. abandoned chicken coops may be a nidus for Histoplasma capsulatum.

Define disease prevention.

A set of measures to prevent the occurrence of a disease or limit its progression and/or severity.

What is a vector?

A vector is a living invertebrate responsible for the transmission of infectious agents.