1.1 Definitions
Over the years, there have been many definitions of epidemiology. Some examples follow:
A.āā¦the study of the health status of populationsā¦ā (Schwabe et al., 1977)
B.āā¦Epidemiology is nothing more than ecology with a medical and mathematical flavor.ā (Norman D. Levine, 1990, personal communication)
C.āThe branch of medicine that deals with the study of the causes, distribution, and control of disease in populations.ā (American Heritage Medical Dictionary, 2007)
D.āThe study of the determinants of disease events in populations.ā (Mosbyās Medical Dictionary, 2009)
E.āEpidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems.ā (World Health Organization, 2019, https://www.who.int/topics/epidemiology/en/)
Common threads in the above definitions are revealed if we consider their origin (Wikipedia contributors, 2019, https://en.wikipedia.org/wiki/Epidemiology). The term epidemiology derives from three Greek words: epi (āaboutā or āuponā), demos (āpopulaceā or āpeople of districtsā), logos (āword,ā thus science or theory). The term epizootiology is sometimes used in reference to comparable studies in animal populations. The distinction is useful when one wishes to describe the state of disease in human or animal populations specifically, particularly when discussing zoonotic disease. For most purposes, however, epidemiology is understood to refer to all animal populations, human and otherwise. Likewise, to avoid confusion, it is preferable to use the term epidemic in lieu of epizootic, and endemic in lieu of enzootic wherever possible. Thus, a simple definition of epidemiology that captures the spirit of earlier definitions and reflects the emphasis of this book is āā¦the research discipline concerned with the distribution and determinants of disease in populationsā (Fletcher et al., 1982).
This definition alone does not appear to provide sufficient grounds for creating a separate discipline. After all, laboratory researchers study disease in populations of animals, populations that may comprise hundreds or thousands of individuals. Furthermore, laboratory researchers address the same sorts of questions as do epidemiologistsāquestions such as the cause, clinical signs, diagnosis, treatment, outcome, and prevention of disease. An important distinction, however, is that epidemiologists study disease in its natural habitat, away from the controlled environment of the laboratory. Epidemiology deals with naturally or spontaneously occurring, rather than experimentally induced, conditions.
The foregoing definitions imply that epidemiology is concerned with the population rather than the individual. To a certain extent this is true. However, an understanding of health and disease in populations is fundamental to medical decision-making in the individual.
The discipline of epidemiology is a critical component of the One Health initiative. One Health focuses on delivering collaborative, multidisciplinary solutions to complex problems at the animal, human, and environmental interface. This approach brings together the strengths of multiple health science professionals including veterinarians, physicians, public health professionals, epidemiologists, ecologists, economists, social scientists, toxicologists, and othersāworking locally, nationally, and globallyāto attain optimal health for people, domestic animals, wildlife, plants, and our environment. Examples of problems that are the focus of the One Health approach are zoonotic and emerging diseases, food safety, antimicrobial resistance, disaster preparedness, and disease surveillance and control in domestic animals and wildlife. One Health embraces the idea that complex problems at the human-animal-environmental interface can best be solved through multidisciplinary communication, cooperation, and collaboration across disciplines and sectors.
1.2 Epidemiologic Approaches
Epidemiology has its roots in disease surveillance and outbreak investigation. Many consider that epidemiology was ābornā during the cholera investigations conducted by John Snow in London in the mid 1800s. However, examples of outbreak investigation can be documented as far back as the Greek and Roman eras (Morens, 2003). Over the years, a number of epidemiologic disciplines and associated methodologies have emerged. These categories are somewhat arbitrary but illustrate some of the ways in which epidemiology contributes to veterinary and human medicine.
1.2.1 Quantitative Epidemiology
Quantitative epidemiology strives to q...
