Epidemiology

The study of the occurrence and distribution and determinants of health related evets, states and processes in specified population • Includes the study of the detriments influences such processes • includes the application of these things

• The frequency of a disease or a condition • The distribution of a disease or condition • Causal factors

• How individuals/populations are affected → clinical signs • What causes →pathogen, causal factors, etc • When they are affected → time or life stage • Who is affected → characteristic of those affected (age, sex, breed, etc) • Where they are affected → location (where is it concentrated) Also state prevalence/incidence and mode of transportation

Host Agent Environment sometimes vector

• Age • Sec • “Use” • Genetics • Immunity (includes vaccination status) • Medical history • Ect

Biological (bacteria, viruses, yeast, ect) Chemical (toxins, poison, feed, ect) Mechanical (physical injury, ect) Nutritional

Geographic location Climate Water supply DOES NOT INCLUDE VACCINATION STATUS

Direct - contact must be made between individuals - Ex. Sexual interaction (contagious equine metris) Indirect - Transmission via a common source (ex. Water source) - Can be a vector or a fomite Vector - Transmission via a living source - Diseases is carried by a vector but doesn’t cause disease - They aren’t sick themselves NOT THE SAME AS CROSS CONTAMINATION Ex. Mosquitoes, ticks, fleas Ex. West Nile, EEE, the plague, Fomite - Transmission via a non-living source - Contaminated needles, boots, ect

Is it in you (vector), or is it on you (fomite)

Continual source of a pathogen in a limited region * It’s in the environment * You can’t really get rid of it

Atypical increased occurrence of an illness in a limited region - Flu season

Increased occurrence of illness that crosses national borders

Epidemic limited to a localized, rapid increase in the incidence of a disease * Small amount * Sudden, rapid

Single point of research - Single point of exposure * One source of exposure to the pathogen at a single point of time Multiple exposure - Multiple sources of exposure or different groups are susceptible at different times * Could be endemic Continuous exposure - A population (or herd) is exposed to a continuous source of disease * Sickness all the time * Could be endemic, epidemic, or pandemic

Incidence - The number of NEW CASES that occur in a population at risk during a specified period of time Can account for risk and rate Prevalence - The number of EXISTING cases in a population at a specific time Could be a single time point or a long term measure (typically the longer term)

Prevalence Useful for assessing health statue of a population * Planning * Chronic diseases (not useful for acute conditions) Incidence Investigation of causation, prevention, and treatments * Planning * Can measure repeated events * (strangles cases, avian influenza, ect)

“Systematic and continuous collection, analysis, and interpretation of data, closely integrated with the timely and coherent dissemination of the results and assessment to those who have the right to know so that action can be taken.”

Passive surveillance * Data from reported cases * Reported by primary care physicians, hospitals, or other healthcare providers * Inexpensive * Completeness and underreporting are issues Active Surveillance * Case finding * Can involve interviewing, reviewing medical records, visiting field sites * Expensive * More accurate reporting

“The presumptive identification of unrecognized disease or defect by the application of tests, examinations, or other procedures which can be applied directly” * FIV testing * Screening for welfare violation * Screening for anatomical variations

• How individuals/populations are affected → clinical signs • What causes →pathogen, causal factors, etc • When they are affected → time or life stage • Who is affected → characteristic of those affected such as age, sex, etc • Where they are affected → location Mode of transportation Incidence/Prevalence

Single point of exposure - Single point of exposure * One source of exposure to the pathogen at a single point of time

Multiple exposure - Multiple sources of exposure or different groups are susceptible at different times * Could be endemic

Continuous exposure - A population (or herd) is exposed to a continuous source of disease * Sickness all the time * Could be endemic, epidemic, or pandemic