EpiLEC Session 3 Population Structure PDF

Course Code: PHLT 2 Veterinary Epidemiology Student Activity Sheet for Session #3 Name: _____________________________________________________________ Class number: _______ Section: ____________ Schedule: _____...

Course Code: PHLT 2 Veterinary Epidemiology Student Activity Sheet for Session #3 Name: _____________________________________________________________ Class number: _______ Section: ____________ Schedule: ________________________________________ Date: ________________ Lesson title: Understanding the Population Structure Materials: - Paper and Pen Lesson Objectives: - Desktop Computer or Smart Phone with At the end of this period, the students are expected to: internet access 1. Describe disease occurrence in populations - pdf file copy of 2. classify contiguous and separated population reference book structures. 3. explain the significance of applying population References: structure in the investigation of disease in 1. Thrusfield, Michael (1995). populations. Veterinary Epidemiology. Third edition. Oxford: Blackwell Science Ltd. 1. 2. Schwabe, Riemann, Franti (1977). Veterinary Epidemiology in Veterinary Practice, Philadelphia: Lea & Febiger. Productivity Tip: Express delight and enthusiasm for everything you do including this course. A. LESSON PREVIEW/REVIEW 1) Introduction (2 mins) At the turn of the 18th century there have been shifts from the traditional medicine having primary emphasis on the individual sick animal evolving to wider emphasis on affected herd or population. The population gradually gained importance as a basic unit of concern in many countries. Epidemiology provided reasons why individuals in a population became diseased and how the condition is controlled or prevented. As we experience in the current Corona virus-19 (Covid-19) pandemic, the number of individuals that are infected is used to estimate workload of front liners, costs for control measures and other management, or the size (capacity) of facilities required to provide adequate health care for people in communities. Essentially, the community quarantines implemented by the government play a role in controlling the spread of coronavirus and thereby render capacity of our health services to address the needs of people. FLM 1.0 Prepared by Daniel C. Ventura, Jr., DVM, PhD., DipVPH  Course Code: PHLT 2 Veterinary Epidemiology Student Activity Sheet for Session #3 Name: _____________________________________________________________ Class number: _______ Section: ____________ Schedule: ________________________________________ Date: ________________ Epidemiologists, further want to estimate the probability of events such as becoming infected, diseased, or dying in populations containing different numbers of individuals. Hence, they express these counts as a fraction of the number of individuals that are likely to be exposed and experience Covid-19. In this session, our focus will be on the population and how disease occurrence is described in a study population. 2) Activity 1: What I Know Chart, part 1 (3 mins) Consider the following questions on the table below. On the first column briefly write in bullet points what you know about the question. Meanwhile, leave the third column blank until you have completed going through the whole lesson. What I Know Questions: What I Learned (Activity 4) 1. How can knowledge on the dynamics of animal population help in understanding patterns of a disease? 2. In which population is an infectious disease more difficult to control a) humans and dogs or b) hogs and broilers? Why? B. MAIN LESSON 1) Activity 2: Content Notes (20 mins) Read the full content of this lesson in the following sources: Thrusfield, Michael (1995). Veterinary Epidemiology Third Edition, pp 50-53 Schwabe, Riemann, and Franti (1977), Epidemiology in Veterinary Practice p 12 Population Units Determining the population of concern is significant in epidemiologic investigations. For most purposes in epidemiology, it is an advantage to know the size of the population being considered, although at times it is enough to observe known samples of that universe or even to work with lesser knowledge of a population. FLM 1.0 Prepared by Daniel C. Ventura, Jr., DVM, PhD., DipVPH  Course Code: PHLT 2 Veterinary Epidemiology Student Activity Sheet for Session #3 Name: _____________________________________________________________ Class number: _______ Section: ____________ Schedule: ________________________________________ Date: ________________ Putt, et.al. (1987) defined population as “the complete collection of individuals that have some particular characteristic(s) in common.” The population size varies depending on the characteristic(s) being considered. Example, when we study rabies among dogs, the population may consist of: All dogs in the Philippines, or all roaming, or owned dogs, or vaccinated and unvaccinated dogs, etc. Meanwhile another significant term in epidemiological studies is population-at-risk which is usually “a subset of the original, defined population and comprises the total number of individuals in that original population that are considered capable of acquiring the disease or disease characteristics being studied (Putt, et.al. (1987))” In our previous example, our focus of investigation for rabies could be unvaccinated, roaming dog population. Stevenson (2005) cited that epidemiologists frequently examine populations to: Detect the presence of a disease; Demonstrate that a disease is not present within a population; and Establish the level of occurrence of a disease within a population To produce accurate estimates of disease we must be able to measure populations effectively. The exact level of disease within a population will be obtained if every individual within the population is examined (and if there was no measurement error). This technique is a census. However, in many situations a census is impossible and/or excessively expensive. Usually an accurate estimate can be obtained by examining some of the animals (a sample) from the population. The object in describing disease events is usually to express data possibly as frequencies (i.e. relative frequencies, proportions, or probability statements). To be significant, the frequency is related to the population in which the event took place. The denominator value in such rates is the population at risk. Along principles of sampling, “a population refers to the whole collection of units (the “universe”) from which a sample may be drawn; not necessarily a population of persons – the units may be institutions, records, or events.” (Dictionary of Epidemiology (2008), edited by M. Porta) A population of animals may therefore be represented by: The individual, e.g. all swine, all sows, all landrace, etc. The measurement of a variable on each animal, e.g. live weight, cortisol or enzyme level, etc. Numbers of items (in a given area, volume or time), e.g. complete blood counts, fecal egg counts, etc. FLM 1.0 Prepared by Daniel C. Ventura, Jr., DVM, PhD., DipVPH  Course Code: PHLT 2 Veterinary Epidemiology Student Activity Sheet for Session #3 Name: _____________________________________________________________ Class number: _______ Section: ____________ Schedule: ________________________________________ Date: ________________ The structure of animal populations The structure of populations influences the extent to which the size of the population at risk can be assessed, as well as affecting the ways in which disease occurs and persists in animals. The organization of animal populations can usually be described as either contiguous or separated. In a contiguous population there is much contact between individuals in the population and members of other populations. Contiguous populations therefore predispose to transfer and persistence of infectious diseases over large areas because of the inherent mixing and movement of animals. Meanwhile, separated populations occur as discrete units such as herds and flocks. A separated population can be closed, with no movement of animals into or out of the unit (except to slaughter). Two extreme examples of closed populations are the specific- pathogen-free (SPF) and gnotobiotic colonies of laboratory animals. A separated population can also be open, with limited movement of individuals in and out. Separated populations, especially of the closed type, are less likely to be infected with agents from other areas than contiguous populations. However, if infection enters separated populations, it may spread rapidly because the animal density frequently is high. Assessing the size of contiguous and separated populations Considering its loose structure, it is often difficult to assess the size of contiguous animal populations while information on the size of a separated population is often easier to obtain. The large numbers of animals kept under conditions of intensive husbandry in a single separated unit usually have only one owner (i.e., the animal:owner ratio is high). Also, many demographic data about food animals are available as a result of regular censuses and estimations. Populations of wild animals can be enumerated either directly or indirectly. Direct methods involve observation of individual animals and include aerial and ground counts. A common method is capture-release-recapture in which animals are caught, marked and released. A second sample is then captured. The numbers of marked animals recaptured in the second sample is then related to the number initially marked. “Capture-release-recapture techniques have also been applied to estimating the size of dog populations (Beck, 1 973; Anvik et ai., 1974; Heussner et ai., 1978); and these and other marking techniques can also provide information on the movement, home range and territories of wild animals, which can be relevant to disease transmission. FLM 1.0 Prepared by Daniel C. Ventura, Jr., DVM, PhD., DipVPH  Course Code: PHLT 2 Veterinary Epidemiology Student Activity Sheet for Session #3 Name: _____________________________________________________________ Class number: _______ Section: ____________ Schedule: ________________________________________ Date: ________________ Supplemental Reading Pfeiffer D. (2002). Veterinary Epidemiology – An Introduction. Available from: http://www.panaftosa.org.br/Comp/MAPA/431857.pdf 2) Activity 3: Skill-building Activities (18 mins + 2 mins checking) Earn total of 10 points 2.1 Check all contiguous population on the list below  a school of fish  a convocation of eagles in a conservation center  a pack of wild dogs  a clowder of cats in a community  a flock of cage-free hens  a colony of rabbits in a forest  a herd of cattle in a ranch  a cloud of bats in a cave  a stud of horse in a stable  a trip of goats 2.2 Additional activity will be uploaded in google classroom. Instructions are likewise provided. Send comment through google classroom or group chat in messenger for concerns. 3) Activity 4: What I Know Chart, part 2 (2 mins) You are about to complete the lesson at this point. To refresh what you have learned, review back the questions in the What I Know Chart from Activity 1 and write your answers to the questions based on what you now know in the third column of the chart. 4) Activity 5: Check for Understanding (5 mins) Take Quiz Uploaded in Google Classroom C. LESSON WRAP-UP 1) Activity 6: Thinking about Learning (5 mins) You are done with this session! Let’s track your progress. Shade the session numbers you have completed. P1 P2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ FLM 1.0 Prepared by Daniel C. Ventura, Jr., DVM, PhD., DipVPH  Course Code: PHLT 2 Veterinary Epidemiology Student Activity Sheet for Session #3 Name: _____________________________________________________________ Class number: _______ Section: ____________ Schedule: ________________________________________ Date: ________________ 2) My learning targets: Complete the table below. Record your scores, learning experience for the session and deliberately plan for the next session. Date Learning Target/Topic Scores Action Plan What session# did you do? What were the What were What contributed to the quality of your performance What’s the date learning targets? What activities did you your scores in today? What will you do next session to maintain today? do? the activities? your performance or improve it? Key to Correction to Activity 2 2.1 Check all contiguous population on the list below Reward yourself five (5) points for complete correct answers in this item. a school of fish  a convocation of eagles in a conservation center a pack of wild dogs a clowder of cats in a community  a flock of cage-free hens a colony of rabbits in a forest  a herd of cattle in a ranch a cloud of bats in a cave  a stud of horse in a stable  a trip of goats 2.2 Additional five (5) point can be earned for correctly answering the exercise uploaded in google classroom FLM 1.0 Prepared by Daniel C. Ventura, Jr., DVM, PhD., DipVPH