Epidemiology Exam 1

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 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

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.

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.

What is a vector?

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

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.

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 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 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

What are the seven sub-disciplines of epidemiology?

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

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.

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.

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 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

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.

Define vehicle or fomite.

Inanimate objects contaminated with infectious agents

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)

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 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 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)

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.)

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 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.

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.

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)

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

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

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

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.

What two factors determine the servival of an infectious agent?

Successful transmission and maintenance of the life-cycle.

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.*

Define infectious dose.

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

Define contact rate.

The rate at which susceptibles interact with infected animals.

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*