Epizootiology

The foundations of epidemiology, including its veterinary applications, can be traced to the mid-19th century. In 1842, Ignaz Semmelweis established an association between clinical practices and maternal mortality from childbed fever at the General Hospital in Vienna, demonstrating that mortality was significantly higher in rooms attended by physicians who had performed necropsies earlier the same day. His recommendation to adopt hygienic protocols reduced mortality to background levels. In 1966, Schwabe established the Department of Epidemiology and Preventive Medicine at the University of California, Davis School of Veterinary Medicine, the first department of its kind in any veterinary school in the world. UC Davis subsequently awarded the world's first doctorate in veterinary epidemiology to Peter Schantz in 1969. Since the mid-20th century, veterinary epidemiologists have continued to apply analytical methods to control diseases even in the absence of complete etiological information. A notable example was the control of the bovine spongiform encephalopathy (BSE) epidemic in the United Kingdom in the late 1980s, where the banning of ruminant-derived proteins in animal feed—based on epidemiological evidence of association—contributed to a decline in disease incidence before a causative agent was fully characterized. == Methods ==

Veterinary epidemiology employs a range of study designs and analytical methods adapted from human epidemiology to investigate disease in animal populations. Study designs The principal study designs used in veterinary epidemiology include: • Cohort study: A group of disease-free animals is followed over time to observe the development of disease in relation to specific exposures. Cohort studies may be prospective (following subjects forward in time) or retrospective (using historical data). The key measure derived from cohort studies is the relative risk (RR). • Case–control study: Animals with a disease (cases) are compared with similar animals without the disease (controls) to identify differences in past exposures. Case–control studies are particularly useful for investigating rare diseases and use the odds ratio (OR) as the primary measure of association. • Cross-sectional study: A one-time assessment of disease frequency in a defined population, useful for estimating prevalence and generating hypotheses for further investigation. An example is a serosurvey of veterinarians for antibodies to Bartonella henselae. • Ecological study: An analysis conducted at the group or population level rather than the individual level. John Snow's investigation of cholera in relation to water sources is a classic example. • Randomized controlled trial: Animals are randomly assigned to intervention or control groups to test the efficacy of treatments, vaccines, or other interventions under controlled conditions. Disease frequency measures Key measures used to quantify disease occurrence in veterinary populations include: • Prevalence: The proportion of existing cases in a population at a given point in time (point prevalence) or over a defined period (period prevalence). • Incidence: The number of new cases arising in a disease-free population at risk during a specified time period. This may be expressed as cumulative incidence (incidence risk) or incidence density (new cases per unit of animal-time). • Attack rate: The cumulative incidence during an outbreak, calculated as the number of new cases since the onset of the outbreak divided by the population at risk. • Case fatality rate: The proportion of individuals with a disease who die from it during a specified time period. Diagnostic test evaluation Veterinary epidemiologists assess the performance of diagnostic tests using measures including sensitivity (the probability of a positive test result when disease is present) and specificity (the probability of a negative test result when disease is absent). Positive predictive value and negative predictive value depend on both test characteristics and the prevalence of the disease in the population being tested. == Disease surveillance ==

Disease surveillance is a core function of veterinary epidemiology, involving the systematic collection, analysis, and interpretation of health data to monitor disease trends and detect emerging threats in animal populations. WOAH Members are required to submit immediate notifications for important epidemiological events, followed by weekly follow-up reports. Six-monthly reports provide information on the presence or absence of listed diseases, quantitative data on outbreaks, and control measures applied. Annual reports, prepared in collaboration with the World Health Organization (WHO) and the Food and Agriculture Organization (FAO), include data on non-listed diseases, the impact of zoonoses on humans, animal populations, and veterinary services personnel. == Connection to One Health ==

Veterinary epidemiology is a key component of the One Health approach, which recognizes that the health of people, animals, and the environment is closely connected and requires interdisciplinary collaboration. The Thailand FETP became the first program to enroll veterinarians, eventually establishing a separate veterinary-specific FETP (FETP-V). In Nigeria, veterinarians are trained in a separate track within the same program, where veterinary epidemiology elements are reflected in course content, field assignments, and post-training deployments. == Applications ==

Veterinary epidemiology has broad applications across several domains: • Zoonotic disease control: Investigating and controlling diseases transmitted between animals and humans, such as rabies, brucellosis, avian influenza, and bovine tuberculosis. • Food safety: Monitoring foodborne pathogens including Salmonella, Campylobacter, and E. coli O157:H7 in animal-derived food products. • Antimicrobial resistance: Surveillance of resistant organisms in animal populations and evaluation of antimicrobial stewardship programs in veterinary practice. • Livestock production: Improving herd health management, productivity, and the economic efficiency of animal production systems. • Wildlife disease: Monitoring disease in wild animal populations, including diseases that may spill over to domestic animals or humans. • Bioterrorism preparedness: Detecting intentional introduction of animal pathogens and supporting emergency response planning. == Modern developments ==

Since the 1990s, veterinary epidemiology has increasingly incorporated geographic information system (GIS) tools, time-series analysis, and geostatistical methods for the spatial and temporal analysis of disease patterns. Advances in hardware and software have enabled the development of surveillance systems capable of near-real-time data collection, analysis, and sharing to support evidence-based policy decisions. == See also ==