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167 Cards in this Set
- Front
- Back
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Historical Approaches to Characterize Disease up to Hippocrates
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environmental and host factors without quantification
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Why is Quantification necessary?
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For assessing the nature and severity of health problems as well as understanding etiology.
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John Graunt
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Mortality data in 1662. Laid groundworks for epidemiology and demography and was the first to quantify patterns of birth, death, and disease occurence noting disparities between male and female, high infant mortality, urban/rural differences and seasonal variations.
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William Farr
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1800s, systematic collection and analysis of Britian's mortality statistics, marital status, occupation, and altitude. Also vital statistics and surveillance.
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John Snow
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Mapped for cholera
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Web of causation
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Emerged in response to chronic diseases with interconnected factors including host and environment. ex. Doll and Hill link smoking to cancer.
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Injuries, violence, and advances in computation
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Expansion of epidemiology to molecular, genetic, computational, and theoretical epidemiology
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Origination of word: epidemiology
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Epi "Upon"
Demos: "The common people" Logos: "Discoursing" Roots in the study of what befalls a population. |
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Epidemiology (2 definitions)
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The study of the distribution (freq, pattern) and determinants of health related states or events in specified population and the application of this study to control health problems.
A branch of science which deals with the dynamics of health/ill health in populations |
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Epidemiology deals with these 9 Principles
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Study, distribution, frequency, pattern, determinants, application, populations, disease, and dynamics.
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This factor is data-driven, systematic and unbiased approach, quantitative discipline, and causal reasoning to explain health-related behaviors, states and events
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Study
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Systematic and unbiased study approach of Epidemiology
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Collection, analysis, interpretation of data, observation and valid comparison groups
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This type of study approach deals with probability, statistics and research methods
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Quantitative discipline.
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This factor deals with characteristics of the host, place, and change over time. (Who is getting the disease, where is it occurring, and how does it change overtime?)
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Distribution factor of Epidemiology
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This factor of epidemiology deals with quantification of how often a disease arises in a population.
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Frequency factor of Epidemiology
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Case definition (clinical, physiological, tests, combinations), instituting mechanism for counting disease (death certificates, reports), and determining size of population. Relating size of population (rate) to epidemiology enables us to compare disease occurrence across different populations.
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Frequency
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Describe the pattern factor of epidemiology.
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Distribution is not random. Differences among population groups subdivided according to age, sex and other demographics, among different countries, a single country, and over time. Subgroups of the populations are more frequently affected than others.
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Diseases that have notable patterns
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Cancer, heart disease, and asthma.
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Little control over biological make-up of disease, lifestyle, and availability and use of health care.
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Determinants
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Analytic epidemiology
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Determine the why and how of disease considering genetic make-up, behaviors, and environmental exposes.
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This factor of epidemiology focuses on reviewing public health problems. By diagnosing a community, one can propose public health interventions to control and prevent disease.
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Application
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Describe the Populations factor of Epidemiology
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Characteristics are personal (age, sex, race, health behaviors), geographical (neighborhood, city, region, country, continent), and time.
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Two aspects of Health
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physical health (fitness) and mental health. Physical: nutrition, exercise. Mental: emotional, psychological, function in society
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Describe the disease factor of epidemiology
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It manifests itself through productivity deficits or lack of quality survivorship. There is no clearcut distinction between healthy and diseased.
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This is the dynamic factor of Epidemiology aka Epidemiologic Systems Model
Healthy -> A-> B-> Mild illness -> C -> D |
A) Exposed but not infected,
B) Infected but not diseased C) Severe illness D) Death |
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In farm animal populations it is more important to know the ___ with which the disease occurs and what its impact is on productivity. Disease may ___ the potential productivity of a given population.
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Frequency
Decrease |
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Clinical disease may not be a limiting factor. What could be a reason for productivity to decrease?
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Sub-clinical diseases such as management deficiencies, for example housing and feeding. It is necessary to determine the determinants (causes of disease).
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Epidemiology provides what to optimize health and productivity? What are two broad uses os epidemiology?
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Guidance. Investigative or diagnostic discipline, and corrective or directed action to prevent or control the disease investigated.
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What are two ways that epidemiology is an investigative or diagnostic discipline?
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1) Utilizes most medicinal sciences. 2) Records disease distribution and occurrence: The where, when, which/who, and why.
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The corrective or directed action to prevent or control the disease investigated is the __ in broad-based use of Epidemiology.
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How
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Epidemiology is used to identify the etiology or causes of a disease and the relevant risk factors associated with it. If the etiology is already known how could epidemiology be facilitated?
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To try and answer why an outbreak has occurred or why the number of cases increased.
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If etiology of a disease is not known how could epidemiology help?
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It could be used to control the disease (ex. CBPP in North America, Edward Jenner, BSE, and John Snow).
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How can etiology help with planning health services and facilities and training future health care providers?
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It can determine the extent (burden) of disease found in the community.
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Epidemiology can provide information for any disease done studies on, and help to implement a disease control system. How can it help make individual decisions on health?
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Epidemiologic information can dictate whether a person decides to smoke, climb stairs rather than wait on an elevator, eat a salad rather than a cheeseburger, or use a condom.
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What is the difference between the usual setting of clinical medicine vs the setting of epidemiology approaches?
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CM occurs in the hospital/clinic, and often is removed from circumstances such as environment or where the disease occurred. Epidemiology occurs at home, school, nursery ,field, farm, feedlot (any setting where the disease occurred)
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What is the primary aim of clinical medicine? Epidemiology?
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CM: Treat the individual
Epi: Control the disease or prevent future occurrence |
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What is the unit of concern in Clinical medicine? Epidemiology?
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CM: Sick person
Epi: Population (Healthy, sick, and dead) |
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What is the diagnostic procedure for clinical medicine? Epidemiology?
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CM: Naming disease on basis of signs, symptoms, largely an organoleptic procedure
Epi: Determination of frequency and pattern of occurrence of disease |
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What are questions asked in clinical medicine? EpidemiologY?
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CM: What is it? How do I treat it? (Restorative medicine)
Epi: What is it? Nature, frequency? Who (Host characteristic), where, when, what caused it (determinant), why does it occur and how is it controlled |
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By studying etiological agents, pathogenesis, and diagnostic techniques, epidemiology is related to these 4 sciences
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Microbiology, toxicology, parasitology and pathology
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In trying to show the character and epidemiological significance of the host, epidemiology interrelates with
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anatomy, physiology, genetics
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Environmental impacts involves epidemiology as well as
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geography, ecology
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Zoonosis involved epidemiology and
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food technology
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Action to take against disease involves Epidemiology and
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pharmacology, immunology
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Epidemiologic Approach
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identifying disease, transition from one state to another (dynamism), determinants and relationship between determinants (causes)
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Determinants of disease
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Factor that can affect frequency with which the disease can occur or the health of populations
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Knowledge of determinants can id categories of animals that pose to what?
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Have a particular risk of developing disease.
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What four types of determinants are there?
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Primary and secondary
Intrinsic and Extrinsic |
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Primary determinants
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Necessary causes, variations cause major effects on disease.
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What are examples of primary determinants?
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Distemper virus or Rinderpest virus
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Secondary determinants
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Predisposing, enabling and reinforcing factors.
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Intrinsic determinants
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Endogenous, genetically governed factors of host, agent, or vectors.
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Extrinsic determinants
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Exogenous, environmental influences which alter disease frequency.
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A disease in which an infectious agent is the main determinant. Host and environment factors are insignificant. 2 examples.
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Simple disease. ex. FMD and Rinderpest
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Complex disease and example
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Multifactorial nature predominates and there is a clear interaction btw agent, host and environment. ex. mastitis
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Do diseases occur randomly? Explain.
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No. It is important to identify factors that place some members at greater risk than others.
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Agent, host and environmental factors
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Etiologic agents directly responsible for disease, multiplication and spread in population.
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Traditional model for infectious disease
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A triad consisting of an external agent, susceptible host, and environment that brings the host and agent together.
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How can one use the traditional model for infectious disease to control or prevent disease?
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It requires assessment of all three components and interactions.
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Agent
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Infectious pathogen, or chemical and physical causes of disease or injury
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Is presence of agent alone always sufficient to cause disease?
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No, many factors influence whether exposure to an organism will result in disease including pathogenicity and dose.
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Pathogenicity
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Ability to cause disease
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Can the traditional model for infectious disease describe diseases such as cardiovascular disease or cancer?
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No, because there are multiple contributing causes.
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Host
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Humans/animals who can get the disease.
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Risk factors of the host
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Factors intrinsic to the host that can influence an individual's exposure, susceptibility or response to a causative agent
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Host susceptibility and response to an agent depend on
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Genetic composition, nutritional and immunologic status, anatomic structure, and psychological makeup
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Environment
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Extrinsic factors that include physical, biologic, and socioeconomic factors.
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What are physical environmental factors?
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Geology and climate
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What are biologic factors?
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Insects that transmit the agent
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What are (environmental) socioeconomic factors
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Crowding, sanitation, and availability of health services
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Why start using Component causes and causal pies (Web of Causation)?
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Agent-host-environmental model did not work for many non-infectious diseases.
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Individual factors of a causal pie
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Component causes
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A complete pie
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Causal pathway, or sufficient cause
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A component that appears in every pie or pathway
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Necessary cause
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Can a disease be made of a single component cause as the sufficient cause?
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No, host susceptibility also needs to be taken into account.
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Can an agent be harmless in healthy people and unhealthy in other conditions?
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Yes. Pneumonocystis carinii harmlessly colonizes respiratory of heathy people, but can be lethal in people with HIV. Therefore Pneumonocystis carinii is a necessary but not sufficient cause of pneumocystis pneumonia.
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Can a particular disease result from a variety of different sufficient causes or pathways?
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Yes. Lung cancer may result from a sufficient cause that includes smoking as a component cause. Smoking is also not a necessary cause. Some pathways will include smoking while others will not.
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Does public health action need to identify every component cause of a disease?
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No. Disease prevention can be accomplished by blocking any single component of a sufficient cause at least through that pathway.
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Host factors that can affect illness
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Inherent, biological, acquired, activities, conditions under which they live
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Inherent host characteristics
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Species, age, sex, race
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Biologic host characteristics
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Immune status
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Acquired host characteristics
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Marital status
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Activities of host
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Drug use, occupation
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Living conditions of host
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Socioeconomic status, access to medical care
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Intrinsic host factors
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Genetic factors
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Ex. of host species disease factor
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Rinderpest, in sheep and cattle, but clinical signs solely appear in cattle.
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Species as source of infection for new infections
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Blue tongue in South Africa from imported Merino sheep, (Imported animals)
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Exs of. Species that are resistant to a disease due to efficacy of immune mechanism, skin thickness, specific or innate immunity, or availability of receptor cells.
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Equines resistant to FMD
Receptor cell ability: Sickle-shaped RBC for malaria |
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Ethnic and racial groups
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Different susceptibility or exposure
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Age
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The single most important intrinsic host factor that causes differences in susceptibility, opportunity for exposure, latency or incubation period of disease, and differing physiologic response.
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Affected age of bacterial and viral diseases
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More fatal in young than in adults
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Affected age of protozoan and rickettsial diseases
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More sever in adults than in young
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Endemic diseases
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Diseases that affect the young population (due to premunity)
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Epidemic diseases
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Affect all ages in a population.
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Blackleg
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Age dependent disease: Occurs in young well fed animals.
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What are 4 intrinsic host factors?
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Species, Ethnic and racial groups, age, sex
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How does sex (male or female) affect disease?
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Males have higher rates of illness and death. Sex-related differences include genetics, hormones, and anatomy.
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Name 3 sex associated diseases.
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Mastitis, milk fever, caliculi.
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What are hormonal diseases associated with sex.
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Females are more likely to develop diabetes, but have lower risk of heart disease (due to higher estrogen lvls).
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What is an example of an occupational sex difference in animals?
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D. immitis in male dogs that go hunting.
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What system in the US is mainly affected by extrinsic factors of disease?
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The husbandry system (fatigued, overworked)
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What are two extrinsic factors that can cause disease?
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Socioeconomic status and environmental factors.
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Explain how socioeconomic status can affect disease.
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Frequency of many adverse health conditions increases with decreasing socioeconomic status. (occupation, income) ex. Infant mortality
Gout and breast cancer are conditions associated with higher socioeconomic status. |
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What two types of environmental factors affect disease?
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Physical (climate, shelter, etc)
Biological (Vector) |
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Climate, a physical environmental disease, can be further subdivided into what two groups?
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Macroclimate and Microclimate.
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Explain macroclimate.
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Weather such as rainfall, temperature, and wind that exposes animals to disease.
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How can temperature cause disease?
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It may be a primary determinant of hypothermia in newborns, a stressor, or a predisposing factor to cause agents.
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Climate, a physical environmental disease, can be further subdivided into what two groups?
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Macroclimate and Microclimate.
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How can wind circulation cause disease?
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May cause agents to get in the lungs such as pasteurellae and other respiratory pathogens.
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Explain macroclimate.
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Weather such as rainfall, temperature, and wind that exposes animals to disease.
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Why is climate significant in disease?
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It may affect the stability of the agent or the transmission of disease (air transmission of FMD or wind carrying vectors such as mosquitos.)
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How can temperature cause disease?
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It may be a primary determinant of hypothermia in newborns, a stressor, or a predisposing factor to cause agents.
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How can wind circulation cause disease?
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May cause agents to get in the lungs such as pasteurellae and other respiratory pathogens.
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Climate, a physical environmental disease, can be further subdivided into what two groups?
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Macroclimate and Microclimate.
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Why is climate significant in disease?
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Affects stability of the agent or transmission of disease (air transmission or mosquitos)
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Explain macroclimate.
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Weather such as rainfall, temperature, and wind that exposes animals to disease.
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How can temperature cause disease?
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It may be a primary determinant of hypothermia in newborns, a stressor, or a predisposing factor to cause agents.
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How can wind circulation cause disease?
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May cause agents to get in the lungs such as pasteurellae and other respiratory pathogens.
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Why is climate significant in disease?
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It may affect the stability of the agent or the transmission of disease (air transmission of FMD or wind carrying vectors such as mosquitos.)
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Microclimate
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Climate occuring in a small defined space such as a macroclimate (stable or barn), terrestrial (over leaves), or biological (over a host's body).
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Shelter
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An environmental cause with positive or negative influences. It can prevent heatstroke, but it can often result in intensification (mastitis).
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Soil
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Cause of disease indirectly (nutritional deficiency), or helps in survival of agents (eggs). feces can cause fungal infections.
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What are examples of biological factors?
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Vectors, wild animals (reservoir of infection) for example Leptospirosis in Nile Valley (Egypt) due to irrigation. Intensification, etc.
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How can analyzing data by place help with control of disease?
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You can identify communities at increased risk of disease, hospitable breeding sites, or availability of vector that transmits the organism. Ex. Lyme disease in wooded areas
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Causes of disease can be external or internal (hormone imbalance). External causes can be living or non-living. What are examples of living and nonliving agents?
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Living: virus, bacteria etc
Nonliving: Chemical, physical, etc. |
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Does there have to be an agent to a disease?
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Yes, if there is a disease there should be an agent.
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Infectivity of an infectious agent
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A measure of an agent's ability to penetrate, multiply, and produce change in a host. Can be expressed qualitatively or quantitatively by ID50 (# of infectious agents required to infect 50%)
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Pathogenicity of an infectious agent
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Measure of an agent's ability to produce clinical disease once it has infected a host
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Virulence of an infectious host
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Measure of the severity of a disease, LD50, Case fatality rate (D/Sick), and either attenuated or enhanced. Passage in less sensitive animals attenuates virulence while passage in sensitive animals enhances virulence.
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Aggressiveness of the infectious agent
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Penetrability, microbial enzymes, reproducibility, inherent ability, and environment within the host.
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Invasiveness of the infectious agent
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Ability of the agent to fight against defense mechanism of the host.
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Toxigenicity of infectious agent
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Measure of disease-causing agent's ability to release toxins (endotoxins or exotoxins)
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Immunogenicity of infectious agent
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Ability of agent to produce a detectable antibody response.
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Plurality of infectious agent
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Antigenic differences of the same species.
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Adaptibility of infectious agent
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Antibiotic resistance factors
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Transmissibility of infectious agent
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Measure of ability of agent to transfer from host to host; means for agents survival
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Stability of infectious agent
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Tenacity, vitality, or duration of organism to remain infective. Certain agents are labile (easily altered; Rinderpest) and some are resistant (FMD).
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Tissue Tropism of infectious agent
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Affinity of the agents to certain tissues. Panthropic (Rinderpest and Canine distemper do not have fixed residing sites), Organothropic (enterp,neuro, or pneum and have certain tissues that they have an affinity to)
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Natural history of disease
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Progression of a disease process in an individual over time in absence of treatment.
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HIV untreated causes a spectrum of clinical problems beginning at the time of seroconversion (primary HIV) and ending in AIDs in around 10 yrs. What is this an example of?
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The natural history of a disease.
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For an infectious disease what is the exposure?
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A microorganism.
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Incubation period
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Time of exposure to onset of disease symptoms in infectious diseases.
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Latency period
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Time of exposure to onset of disease symptoms in chronic diseases.
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During the incubation/latency period are there symptoms?
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No, asymptomatic.
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Incubation period of FMD
Latency period of leukemia |
21 days
6-7 yrs |
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Why are screening programs important to identify disease processes during the latency/incubation period?
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Intervention at this early stage is likely to be more effective than treatment.
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What marks the transition from subclinical to clinical disease?
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Onset of symptoms.
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Do disease processes always progress to clinically apparent illness?
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No, but in some disease processes may result in mild to severe to fatal. This is called spectrum of disease.
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Spectrum of disease
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The length of the disease process and progression of disease.
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Carriers
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Persons who are infectious but have subclinical diseases or who appear to have recovered but remain infectious (ex. chronic carriers of hep B virus)
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Simple establishment of Agent-Host interaction
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Agents cause infection
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Derangement in physical state of the host in Agent-Host interaction
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Agents cause disease.
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What three factors govern agent-host interaction?
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Host resistance (Prior infection with TB makes animal more susceptible), Pathogenicity/virulence of agent (pathogenicity inc. as agents pass in sensitive animals), and predisposing/stress factors
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Predisposing/stress factors of agents
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An environmental impact. Agent can increase its survival by increasing infectivity and decreasing pathogenicity or through shorter generation intervals. Chronic disease agents have these characteristics.
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Death of host is a predisposing determinant, and transmission is enhanced by flesh eating animals to perpetuate cycle in what disease agent?
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T. spiralis
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Why are disease causing agents continuously evolving?
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They have short generation intervals and try to overcome defense ability of the host by antigenic variation and creation of a carrier state.
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Is host/agent relationship a natural phenomenon?
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No. This is why disease processes do not occur randomly.
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Antigenic variation
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Agent evades host defense by changing antigenic characteristics as a result of mutation or genetic recombination of outer proteins.
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What is an important factor in antigenic variation?
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Natural selection
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Carrier
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Any animal that sheds an infectious agent without demonstrating clinical signs.
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What is an important factor in antigenic variation?
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Natural selection
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Carrier
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Any animal that sheds an infectious agent without demonstrating clinical signs.
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Incubatory carriers
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Excrete the agent during the disease's incubation period (Rabies)
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Convalescent carriers
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Shed the agent when they are recovering (FMD)
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Incubatory carriers
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Excrete the agent during the disease's incubation period (Rabies)
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Convalescent carriers
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Shed the agent when they are recovering (FMD)
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