Population Dynamics and Disease Occurrence

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Questions and Answers

What does morbidity refer to in the context of disease?

The amount of disease present in a population (correct)

The duration of a disease outbreak

The number of deaths in a population

The places where a disease occurs

How is the attack rate defined?

The proportion of the population without the disease

The likelihood of disease transmission within a population

The number of deaths occurring in a population

The proportion of animals that develop the disease in a population at risk (correct)

What is indicated by the term 'secondary attack rate'?

The total number of deaths in a population from all causes

The measure of disease prevalence in a population

The number of new cases arising from contact with the primary case (correct)

The proportion of primary cases that die from the disease

In which type of population is there significant contact among individuals and with other populations?

Contiguous population Signup and view all the answers

What does cumulative mortality measure?

The total mortality rate for all diseases Signup and view all the answers

How is case fatality expressed?

As a percentage of deaths to diseased animals within a specific time Signup and view all the answers

What is the main purpose of capture-release recapture methods in wildlife populations?

To estimate population size Signup and view all the answers

What does spatial distribution describe in disease occurrence?

The locations where the disease is found Signup and view all the answers

What does 'virulence' refer to in the context of infectious agents?

The ability of an infectious agent to cause disease Signup and view all the answers

Which of the following describes a cyclopropagative transmission method?

Agent multiplies and then undergoes development in the vector Signup and view all the answers

Which factor is NOT associated with the spread of infection?

Symptom severity in infected individuals Signup and view all the answers

What term describes an infection that does not show clinical symptoms?

Inapparent infection Signup and view all the answers

Which type of transmission is achieved through medical procedures or practices?

Iatrogenic transmission Signup and view all the answers

Which of the following describes 'vertical transmission'?

Disease passed from mother to offspring through genetics Signup and view all the answers

Which characteristic is critical for maintaining infection in a population?

Effective contact among individuals Signup and view all the answers

What does 'pathogenicity' specifically refer to?

The intrinsic ability of an agent to induce disease Signup and view all the answers

What does nidality refer to in landscape epidemiology?

Natural homes of a disease within the ecosystem Signup and view all the answers

Which scale of measurement is best used for ranking groups based on conditions?

Ordinal scale Signup and view all the answers

What type of data is generated by measurements like body weight?

Continuous data Signup and view all the answers

Which of the following is NOT an objective of landscape epidemiology?

Assessing social impacts of disease outbreaks Signup and view all the answers

What is a characteristic of the ratio scale in measurement?

It includes a true zero point and allows for comparison of ratios Signup and view all the answers

What is meant by horizontal transmission in the context of disease transmission?

Direct or indirect disease transmission between any segments of the population. Signup and view all the answers

Which of the following correctly defines a definitive host?

A host in which the organism undergoes its sexual phase of reproduction. Signup and view all the answers

What does the term 'primary host' refer to?

The host that maintains the infection within an endemic area. Signup and view all the answers

Which of the following factors can regulate population size in an ecosystem?

Competition, predation, and availability of resources. Signup and view all the answers

Which best describes indirect horizontal transmission?

Infection spread through vehicles like contaminated water or surfaces. Signup and view all the answers

Which type of ecological zone is characterized by high moisture and diverse plant life?

Megatherms. Signup and view all the answers

What role does a secondary host play in the life cycle of an infectious agent?

It assists in the life cycle without being the primary maintainers. Signup and view all the answers

How can climate influence population dispersal in ecosystems?

It affects both resource availability and reproductive success. Signup and view all the answers

What is the term used to describe the area that an animal defends aggressively within its home range?

Territory Signup and view all the answers

Which of the following describes a common source epidemic?

All cases originate from a single common source. Signup and view all the answers

What does the Wynne-Edwards hypothesis suggest about the purpose of group behavior in populations?

It is mainly for population control. Signup and view all the answers

What defines the temporal distribution of disease as cyclical trends?

Regular, periodic fluctuations in disease levels. Signup and view all the answers

Which of the following is an example of epidemiological interference?

One organism preventing another from establishing. Signup and view all the answers

Which factor is commonly associated with seasonal trends in disease incidence?

Climate variations Signup and view all the answers

What do primary cases in a propagating epidemic do?

Excrete the infectious agent to infect others. Signup and view all the answers

What represents different levels in a food chain?

Trophic levels Signup and view all the answers

Study Notes

Describing Occurrence of Disease

Morbidity refers to the amount of disease in a population, while mortality refers to the number of deaths.
Temporal distribution refers to the times of occurrence of disease cases, while spatial distribution describes where the disease occurs.
Demography involves measuring and describing the size and characteristics of populations.

### Structure of Animal Populations

Contiguous populations have a lot of contact between individuals within the population and with other populations.
Wild animal populations can be estimated through aerial and ground counts, or through capture-release-recapture techniques, where a sample of animals is caught, marked, and released. A second sample is then captured.
The formula to estimate the number of animals (N) is N = an/r, where:
- a = size of the first sample
- n = size of the second sample
- r = number of marked animals in the second sample

### Agent Determinants

Virulence refers to an infectious agent's ability to cause disease, while pathogenicity is the quality of disease induction.
Inapparent infections are infections without clinical signs.
Clinical infections produce noticeable symptoms.
Outcomes of infection can include:
- Carrier state (incubatory, convalescent): a person or animal carrying a pathogen without showing signs of disease.
- Latent infection: a pathogen existing in the body without causing disease.

### Transmission and Maintenance of Infection

Horizontal transmission occurs when a disease moves from one part of the population to another.
- Direct transmission involves physical contact or contact with discharges from an infected host.
- Indirect transmission uses a vehicle to spread the disease, which could be living or inanimate.

### Host and Vector

A host is any plant, animal, or arthropod that can be infected with an infectious agent.
Replication or development of the agent usually occurs in the host.
Types of hosts and vectors include:
- Definitive host: an organism undergoing its sexual phase of reproduction.
- Final host: another term for definitive host.
- Primary host: the animal that maintains the infection in the endemic area.
- Secondary host: an additional species involved in the life cycle of an agent.
- Vector: an organism that carries a pathogen from one host to another.
- Developmental transmission: the essential stage of development of the agent occurs in the vector, such as with Dirofilaria immitis.
- Propagative transmission: the agent replicates within the vector, such as with viruses in ticks in louping ill.
- Cyclopropagative transmission: a combination of developmental and propagative transmission, such as Babesia in ticks.

### Environment as a Determinant

The location, climate (microclimate and macroclimate), and husbandry practices all influence the spread of disease.
Husbandry practices include housing, diet, management, and stress.
Methods of transmission include ingestion, aerial transmission, contact, inoculation, iatrogenic (created by a doctor), coitus, and vertical transmission.
- Vertical transmission: disease acquired either in utero or in ovo (hereditary or congenital).

Ecology of Disease

Landscape epidemiology explores how diseases relate to the ecosystem.
Basic ecological concepts relevant to disease:

### The Distribution of Population

Vegetational zones:
- Megatherms (rainforests): organisms adapted to hot temperatures.
- Mesotherms (deciduous forests): organisms adapted to moderate temperatures.
- Xerophiles (deserts): organisms adapted to dry climates.
Bronies or life zones: areas with particular ranges of plants and animals.
- Tropical rainforest
- Savannah
- Tundra

Regulation of Population Size

Balance of nature: population becomes stable with the rate of reproduction equaling the death rate.
Density-dependent control of population size: competition between individuals drives population size.
Dispersal: survival over a large area often controlled by climate and competition for food.
Predation
Infectious disease

The Niche

A specific position an organism occupies in the environment.
Examples of niches relating to disease:
- Louse infestations
- Intracellular parasitism
- Epidemiological interference: one organism filling a specific niche that prevents another organism from occupying it.

Food Chain

Different trophic levels in the food chain.
Significance of food webs to disease transmission.

### Landscape Epidemiology

The study of diseases in relation to the ecosystem.
Nidality: areas that have ecological, social, and environmental conditions suitable for a disease to thrive.
Nosogenic territory: the natural home of a disease.
Objectives of landscape epidemiology: understanding how ecological factors influence disease occurrence and developing appropriate control strategies.

### Patterns of Disease

Epidemic curves represent the number of new cases of a disease over time.

### Epidemic Curves

Common source and propagating epidemics:
- Common source epidemic: all cases are infected from one source.
- Propagating epidemic: initial cases excrete the agent and infect susceptible individuals, creating secondary and subsequent cases.

Temporal Distribution of Disease

Trends in temporal distribution:
- Cyclical trends: regular, periodic fluctuations in disease occurrence over a 3-4 year cycle.
- Seasonal trends: periodic fluctuations in disease incidence related to specific seasons.

Scales of Measurement

Data types:
- Discrete data: whole numbers (e.g., number of teats in a sow).
- Continuous data: values within a defined range (e.g., girth of a cow, body weight).
Scales of measurement:
- Nominal: use of numbers or symbols for classifying objects (e.g., male and female coded as 1 and 2).
- Ordinal: allows groups to be ranked relative to one another (e.g., carcass condition score scale).
- Interval: distance between ranked values (e.g., Celsius temperature scale).
- Ratio: internal scale with a true zero point (e.g., weight).
- Visual analogue scales (VAS): use a straight line to represent a range of values.

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Description

Explore the concepts of morbidity, mortality, and the demographic characteristics of populations in this quiz. Additionally, understand the structure of animal populations and methods used for estimating their sizes. Test your knowledge on the distribution of diseases and the factors influencing populations.