Veterinary Epidemiology

Veterinary epidemiology is a specialized area within veterinary medicine that was historically termed epizootiology until the mid-1990s. Like human epidemiology, it involves identifying risk factors for diseases, characterizing outbreaks, quantifying incidence and prevalence, describing the natural history of disease, developing disease control and prevention programs, and assessing the effectiveness of these [Page 1080]programs. Veterinary epidemiologists participate in these activities in both human and animal populations when disease agents are zoonotic (infectious and capable of spreading between animals and people), although the potential impacts of environmental agents (σuch as pesticides) on animal and human health and the challenges of cancer and of chronic diseases are also topics for investigation. Veterinarians are trained in medicines of all species, including primates, and so are often involved in identifying disease risks to humans after being alerted to health issues in animals. This can be used in health surveillance, with animals acting as sentinels of human health concerns. One classic example was the use of canaries to detect toxic gases in coal mines.

The concept of ‘one medicine’ was described and expanded by visionary veterinary epidemiologist Calvin Schwabe in the 1980s and refers to the common basis of veterinary and human medical knowledge that can be applied to diseases affecting all species. The value of veterinarians and veterinary epidemiologists in active participation in global health research activities has been recognized fairly recently. As in human epidemiology, a primary goal of veterinary epidemiology is prevention of disease rather than treatment.

From ancient times, it has been important to identify patterns of disease in herds and groups of animals used for human consumption (milk, meat, fiber, and eggs) and activities (transportation and farming), and veterinary medicine had its foundations in the treatment of large animal diseases that have financial and survival consequences. As urban centers increased and smaller animals joined human households as companions, veterinarians have expanded their services to include cats, dogs, mice, rats, ferrets, rabbits, birds, and other creatures small enough to coexist in these smaller spaces. Because veterinarians have been trained to identify and treat diseases in groups or herds, they are well suited for and often ‘automatically’ engaged in epidemiology and, by extension, public health. While veterinary epidemiology has focused on herd health, that is, on disease patterns in large groups of cattle and other farmed animals, the same principles of recognition and control of infectious diseases hold true in large groups of small animals, such as in catteries, breeding kennels, and animal shelters, as well as in veterinary hospitals, where nosocomial (hospital-based) infections are also of concern.

Veterinary epidemiology uses the same tools as human epidemiology, including observational studies, cross-sectional and longitudinal studies, case-control studies, prospective studies, and experimental and field trials of vaccines, diagnostic procedures, medicines, and treatment protocols. Case reports and case series are often reported by veterinarians engaged in clinical practice. Veterinary epidemiologic research often involves methodologic issues, such as sampling techniques for herds and wildlife populations, and appropriate statistical applications to analyze complex data sets such as capture/recapture data. In survey-based studies, veterinary epidemiologists rely nearly exclusively on proxy respondents, such as owners or farmers, for observations and accurate histories of the animals in their care. Observational studies of animal diseases often depend on recruitment of producers (farmers) and owners of small animals contacted through advertisements in publications of trade associations and breed clubs, or through veterinarians to their clients. An area of considerable study is the determination of test characteristics (σensitivity and specificity) for rapid, portable diagnostics used to screen animal populations for common diseases for which ‘gold standard’ testing is too expensive to be used on individual animals. Geographical information system software has been employed to track distributions of herds or disease vectors, the appearance of new disease cases over time (σuch as of avian influenza), and changes in vegetation (food and shelter habitat for desirable and parasite species) due to weather patterns. Modeling of disease reservoirs and agent transmission has been used to predict outbreaks; other models have been used to show how population sizes may change through implementation of oral contraceptive baiting schemes. As in human epidemiology, a concern in disease reporting is correct identification of denominators, which poses a greater challenge than in human epidemiology because no systematic census exists for wildlife or companion animals.

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