Lecture 16 - Measuring Disease Part 1 PDF

Measuring disease – Part 1 Time = 8:30 AM  Outline of Measuring Disease Part 1 Iceberg model of infectious disease – clinical cases are the tip of the iceberg Define incubation period, latent period, illness, and infectious period Define outbreak, epidemic,...

Measuring disease – Part 1 Time = 8:30 AM  Outline of Measuring Disease Part 1 Iceberg model of infectious disease – clinical cases are the tip of the iceberg Define incubation period, latent period, illness, and infectious period Define outbreak, epidemic, pandemic, endemic Monitoring outbreak requires case definition (suspected, probable, confirmed) Measures of disease risk include prevalence and incidence Prevalence is the proportion of animals that have the disease at an instant in time Incidence is the number of new cases in specified time interval Incidence risk is probability of an animal (or person) becoming a case (i.e., getting the disease of interest) over a specified time interval  Iceberg model of infectious disease Only a fraction of animals may show clinical signs of disease Tip of iceberg are animals that are dying, have severe or mild disease Probability to recognize severe disease is high Bottom of iceberg: asymptomatic or subclinical animals with no obvious signs, exposed animals, immune animals Bottom influences disease dynamics Probability to recognize asymptomatic infections is low Asymptomatic, exposed and recovered animals are critical for disease dynamics  Quantifying the course of infectious disease Incubation period Illness Recovered or dead Start of Latent period Infectious period Clearance infection (Not infectious or dead) Progression of disease and transmission over course infection is critical for epidemiology and surveillance Differentiate between development and duration of illness versus infectiousness (i.e., transmission) Illness and infectiousness do not overlap 100% Veterinarian: Incubation period -> illness -> recovery or death Epidemiologist: Latent period -> infectious period -> recovery or death  Quantifying the course of infectious disease No signs Signs Incubation period Illness Recovered or dead Start of Latent period Infectious period Clearance infection (Not infectious or dead) Hosts can’t Hosts can Question: What is the transmit pathogen transmit pathogen asymptomatic infectious period?  Example of Johne’s disease Johne’s disease = paratuberculosis Mycobacterium avium paratuberculosis (MAP) MAP lives in macrophages in small intestine Infected cows shed MAP in their feces Susceptible calves acquire infection by ingesting contaminated fecal material, milk, colostrum Clinical signs: chronic diarrhea, weight loss, no fever. Late stages animals waste and die MAP thickens mucosa, low nutrient absorption Infected animals can shed MAP for years before developing clinical signs Most infected animals are subclinical.  Life cycle of infection with MAP Stage 1 (birth to 6 months): Calves become infected but are not shedding MAP in their feces (i.e., they are not infectious). Stage 2 (2 to 6 years): Cows are subclinical (or asymptomatic); they do not show any clinical signs, but are shedding MAP in their feces. Stages 3 and 4 (2 to 8 years): Cows show the clinical signs of Johne’s disease Veterinarians will recognize Johne’s disease in cattle in stages 3 and 4, and are unlikely to detect disease in animals in stages 1 and 2 Activity: Quantify course of Johne’s disease using arrow diagram Time = 8:40 AM  Quantifying the course of Johne’s disease Incubation period Illness 5 years (2 – 8 years) (5 years to death) Start of Latent period Infectious period infection 4 years (2 – 6 years) (4 years to death) Illness and clinical signs occur at a mean of 5 years (range 2 to 8 years) Infectious period and shedding of MAP occurs at a mean of 4 years (range 2 to 6 years) Cattle become infectious before showing clinical signs. Average asymptomatic infectious period of 1 year  Quantifying the course of rabies Rabies Incubation period (Illness) Dead (3 to 12 weeks) (7 days) Start of Latent period Infectious Dead infection period (5 days) Incubation period of rabies ranges from 3 to 12 weeks During incubation period, virus migrates from bite wound to brain Duration of rabies (illness) is short (7 days) and ends with death Infectious period is slightly shorter (5 days) because virus must migrate from brain to salivary glands Rabies is example of where clinical signs occur before infectiousness (opposite of Johne’s disease)  Determination of the incubation period and the latency period for SARS-CoV-2 Incubation and latency periods were unknown at start of COVID-19 Study from NEJM on business meeting in January 2020 in Munich, Germany Index patient was businesswoman from Shanghai, China infected with SARS-CoV-2 Index patient met with German businessman (patient 1) on Jan 20 and 21. Fell ill on flight back to China Patient 1 contacted patient 3 on Jan 20 and 21 and patient 3 became ill Activity: Use data on patients 1 and 3 to calculate incubation and latent periods for SARS-CoV-2  Individual variation in the duration of the incubation period and latency period Variation in incubation and latency periods among individuals Human volunteers were infected with influenza virus and monitored for shedding and symptoms Incubation and latent periods are short (~1 day) Most patients develop symptoms and start shedding at the same time Activity 1: Compare duration of incubation period and illness for patients 3 and 4 Activity 2: Compare duration of latent and infectious period for patient 9 versus patients 11 and 12 Question: Which individuals are most likely to see a doctor? Which individuals will contribute most to the spread of influenza? Duration of latent period influences disease dynamics Different pathogens can have very different dynamics MAP has latent periods that are measured in years, which means that the dynamics of this pathogen are slow, and an outbreak of Johne’s disease is measured over years In contrast, SARS-CoV-2 and influenza have latent periods that are measured in days, which means that the dynamics of these viral pathogens are fast, and an outbreak of these viral pathogens is measured in weeks or months In summary, outbreaks can occur over weeks or over years depending on the latent period of the disease  Outbreak definition Time = 8:50 AM An outbreak is an increase (often sudden) in the observed number of cases of a disease or a health problem over a time interval (e.g., year) in a host population (e.g., animals or people) compared to the expected background number of cases for that host population in that place (rural municipality, province, country). The expected number of cases for the host population in that place would be based on history (i.e., past years). Question: What is the difference between outbreak, epidemic, endemic, pandemic?  Outbreak, Epidemic, Endemic, Pandemic Outbreaks and epidemics are synonyms Outbreak is often used for more localized epidemics (e.g., village, town) Pandemics are outbreaks or epidemics that occur over a very wide area, affecting a large proportion of the population in several countries and/or continents Endemic disease is a disease that is “normally” present in a population Activity: Classify COVID-19, bovine respiratory disease, and avian influenza in dairy cows as an epidemic, pandemic, or endemic Measuring disease requires a case definition of disease Measuring disease requires a case definition A case definition is a standard set of criteria that scientists use to decide whether an individual should be classified as having the disease of interest Case definitions help to count cases consistently over time and space Case definition is important for comparing observed to expected cases to determine whether the outbreak is real Case definitions often contain a laboratory test, but this is not always necessary  Categories of Case Definitions Case definitions are often placed into categories that differ with certainty/quality of evidence: suspect < presumptive < confirmed Types of evidence considered include (1) clinical signs, (2) epidemiological link to a confirmed case, (3) laboratory test Clinical signs: number of typical clinical signs. Pathognomonic signs (e.g., erythema migrans for Lyme disease) may have more weight than non-specific signs (e.g., fever) Epidemiological link: animal can be linked to a confirmed case Laboratory test: serological tests, nucleic acid tests (PCR), nucleic acid sequence The confirmed case is often evidence of suspect case + additional evidence  National surveillance case definitions for COVID-19 Confirmed case is a person with confirmation of infection with SARS-CoV-2 1) The detection of at least 1 specific gene target by a validated laboratory-based nucleic acid amplification test (NAAT) assay (e.g. real-time PCR or nucleic acid sequencing) performed at a community, hospital, or reference laboratory OR 2) The detection of at least 1 specific gene target by a validated point-of-care (POC) NAAT that has been deemed acceptable to provide a final result (i.e. does not require confirmatory testing) OR 3) Seroconversion or diagnostic rise (at least 4-fold or greater from baseline) in viral specific antibody titre in serum or plasma using a validated laboratory-based serological assay for SARS-CoV-2 Question: Which of these 3 criteria is unlikely to still be valid and why? This example shows that case definitions can change over time  USDA case definitions for foot-and-mouth disease 3.1 Suspect Case: An FMD-susceptible animal with: 3.1.1 Clinical signs consistent with FMD; OR 3.1.2 Epidemiological information indicative of FMD; OR 3.1.3 Non-negative result by a serological antibody screening assay conducted as part of a national surveillance activity 3.2 Presumptive Positive Case: A suspect case with: 3.2.1 Non-negative test result for FMDV from a laboratory other than the National Veterinary Services Laboratories (NVSL). Tests positive on 1 of 5 different tests that identify host antibodies to FMDV proteins or nucleic acid 3.3 Confirmed Positive Case: 3.3.1 FMDV that has been isolated and sequenced at NVSL OR 3.3.2 An FMD susceptible animal with clinical signs consistent with FMD or epidemiological link to FMDV or cause for suspicion of previous association or contact with FMDV; AND Tests positive on 1 of 3 different tests that identify host antibodies to FMDV proteins or nucleic acid. Test must be performed by the NVSL.  Total cases of COVID-19 by province as of 7 October 2021 Alberta has 305,765 cases, whereas PEI Province Total Cases only has 303 cases British Columbia 19,124 Alberta 305,765 Alberta has 1009x more cases of Saskatchewan 69,809 COVID-19 than PEI!!! Manitoba 61,126 Alberta is bigger and has much more Ontario 589,517 people than PEI Quebec 413,306 New Brunswick 4,741 To compare risk of disease, standardize Nova Scotia 6,864 number of cases to size of population at PEI 303 risk of getting COVID-19 Newfoundland/Labrador 1,833 It’s all about the denominator! Yukon 783 Northwest Territories 1,305 Time = 9:00 AM Nunavut 664  Number of COVID-19 cases by province Province Total Cases Population Cases/10^4 people British Columbia 191,124 5,000,879 382.2 Alberta 305,765 4,262,635 717.3 Saskatchewan 69,809 1,132,505 616.4 Manitoba 61,126 1,342,153 455.4 Ontario 589,517 14,223,942 414.5 Quebec 413,306 8,501,833 486.1 New Brunswick 4,741 775,610 61.1 Nova Scotia 6,864 969,383 70.8 PEI 303 154,331 19.6 Newfoundland/Labrador 1,833 510,550 35.9 Yukon 783 40,232 194.6 Northwest Territories 1,305 41,070 317.8 Nunavut 664 36,858 180.2 For each province, divide total cases by population size and multiply by 10,000 Standardized number of COVID-19 in Alberta is 36.5x higher than PEI  Measures of disease risk Measures of disease risk include prevalence and incidence Prevalence of infectious disease is the proportion (or percentage) of cases or infections in our population of interest at a moment in time. Prevalence can be expressed as a proportion (range from 0 to 1) or a percentage (range from 0% to 100%) Prevalence is probability of an animal being infected at a given point in time Prevalence makes no distinction between new and old cases  Prevalence and the sampling interval Ideally, sample population in short time interval (i.e., no recoveries or new infections) to obtain snapshot of the prevalence at a moment in time Accuracy of prevalence estimate depends on dynamics of disease relative to time interval used to sample population Fast- versus slow-moving diseases must be sampled over appropriate time scale (weeks versus months, respectively) Sampling population might take weeks or months during which infections are lost or gained (i.e., recoveries or new infections) This is OK for infectious diseases with slow infection dynamics (e.g., Johne’s disease) because prevalence might not change much over the sampling period  Example calculation of prevalence of lameness in dairy cows You check your herd of 200 dairy cows and identify 20 cows that are lame The prevalence of lameness is 20/200 = 0.10 or 10.0% Example calculation of Johne’s disease in beef cattle in Western Canada Determine prevalence of Johne’s disease in beef cattle in Western Canada (AB, SK, MB) Animals blood sampled from Sep 2014 to Jan 2015. Use ELISA to detect antibodies to MAP 1811 cattle were blood sampled from 93 different herds in 3 prairie provinces. Seroprevalence in cows was 1.55% (28/1811) 23.7% of herds (22/93) had at least 1 seropositive animal 5.0% of herds (5/93) had at least 2 seropositive animals  Incidence In contrast to prevalence, the incidence measures the occurrence of new cases of disease (or some other outcome) during a defined interval of time All measures of incidence should have a time component associated with it Two methods of expressing incidence: (1) incidence risk and (2) incidence rate Incidence risk is the probability that a susceptible animal will contract or develop the disease of interest during a defined interval of time Incidence rate is the number of new cases of disease in a population per unit of animal time during a given time interval Time = 9:10 AM  Incidence risk Number of new disease cases during time interval Incidence risk = Number of individuals at risk at start of time interval Incidence risk is the number of new cases in a time interval divided by the total population at risk at start of the time interval Incidence risk is the proportion (or percentage) of individuals that develop an infection over a defined time interval Incidence considers new cases only, old cases are excluded from the calculations Incidence risk is a measure of the risk of becoming a case during a defined time interval Incidence risk cannot be interpreted without a time interval! Question: Why can incidence risk not be interpreted without a time interval?  Incidence risk continued … The duration of the time determines the probability that the event will happen (i.e., the incidence risk) The risk of an event happening (e.g., getting a disease, dying, etc.) accumulates with the passage of time The incidence risk of a dairy cow acquiring a case of clinical mastitis is higher for 52 weeks compared to one week Incidence risk is a good measure for static populations that are not changing in size Incidence risk is a good measure when the risk period is related to a specific event in the life history of the animal or human (e.g., adolescence, pregnancy, birth)  Example calculation of incidence risk A cattery with 100 cats is experiencing an outbreak of feline viral rhinotracheitis (FVR). During week 1, 20 cats develop FVR. During week 2, 8 more cats develop FVR Calculate incidence risk for week 1, week 2, and weeks 1 and 2 combined Incidence risk for week 1 is 20/100 = 0.20 per week Incidence risk for week 2 is 8/80 = 0.10 per week Incidence risk for 2 weeks is 28/100 = 0.28 per 2 weeks Notice calculation in week 2, excludes cats that became infected in week 1 Notice incidence risk is reported with time interval (1 week, 2 weeks)  Incidence risk of death during childbirth In 19th century, women experienced very high mortality during childbirth due to unhygienic medical practices and puerperal fever Puerperal fever is a bacterial infection of the female reproductive tract following childbirth or miscarriage Monthly incidence risk of death during childbirth at Vienna General Hospital from 1841 – 1849 shows percent of women that died during childbirth Doctors used same tools to perform autopsies and deliver babies with no sterilization or hand washing In 1847, Dr Ignaz Semmelweis introduced a chlorine handwash and incidence risk in maternity clinic dropped from 18% to < 2% This is an example of where the incidence risk is calculated for a specific event (childbirth) and so there is no associated time interval  Dr Ignaz Philipp Semmelweis (1818-1865) Ignaz Semmelweis (1818 – 1865) was a Hungarian doctor at Vienna Hospital who noticed association between poor hygiene and puerperal fever In 1861, he published a book on his findings. Medical establishment ridiculed his findings. He died in an asylum in 1865 at age of 47 years 20 years later, Semmelweis was vindicated by Pasteur and medical establishment recognized the importance of hygiene The Semmelweis effect or Semmelweis reflex is the human tendency to reject new evidence or ideas that contradict established beliefs  Summary of Measuring Disease Part 1 Quantify the course of infectious disease for Johne’s disease and rabies Define incubation period, latent period, illness, and infectious period Define outbreak, epidemic, pandemic, endemic Monitoring outbreak requires case definition (suspected, probable, confirmed) Measures of disease risk include prevalence and incidence Prevalence is the proportion of animals that have the disease at an instant in time Incidence is the number of new cases in specified time interval Incidence risk for time interval (e.g., weekly risk of FVR in a cattery) Incidence risk for an event (e.g., female mortality during childbirth) Time = 9:20 AM End of course # 16  Examples of familiar incidence rates Annual death rate. Number of deaths per 1000 inhabitants per year. Canada has 8.2 deaths/1000 inhabitants whereas the Ukraine has 18.6 deaths/1000 inhabitants. Total fertility rate per woman. The average number of live births a woman would have by age 50 (time interval is reproductive lifespan). Canada has 1.5 births per woman, Niger has 6.6 births per woman, South Korea is 0.9 births per woman Annual intentional homicide rate. Number of intentional homicides per year (excludes war-related deaths, suicide, non-intentional homicide). Canada has 2.273 homicides per 100,000 inhabitants, whereas Haiti has 40.845 homicides per 100,000 inhabitants. Lung cancer rates. Number of patients diagnosed with lung cancer per year (standardized for age structure). China has 40.8 cases per 100,000 inhabitants, which is considerably higher than the world average of 23.6 cases per 100,000 inhabitants Annual incidence of tuberculosis in Canada by population Incidence of slow-moving infectious diseases like tuberculosis (TB) is often expressed per year. Compare annual incidence of TB among population subgroups. Annual incidence of TB in Inuit (188.7 cases per 100,000) is 472x higher compared to Canadian-born, non-Indigenous populations (0.4 cases per 100,000) Reasons include poverty, crowded and poor-quality housing, malnutrition, barriers to health care, mistrust of Western medicine  Incidence rate formula for constant population Number of new disease cases during time interval Incidence rate = Number of animal − time units at risk during time interval An animal time unit is one animal for a defined time interval (dog-days, cow-months, person-years). Chosen time unit (days, years) will depend on disease dynamics Incidence rates often calculated using first occurrence of the disease for each animal Once an animal has had the disease it is no longer part of the population at risk If an animal can be infected with the same disease on multiple occasions than this situation can be accommodated  Incidence rates have a time unit Incidence rate is the number of new cases per unit of animal time Incidence rate measures the rapidity with which new cases develop over time Example: 50 cats in a cattery experience 10 cases of FVR in a one-year period Activity: calculate the incidence rate per year, per month, and per week IR = 10 cases/(50 cats x 1 year) = 10 cases/(50 cat years) = 0.20 cases/cat year IR = 10 cases/(50 cats x 12 mo) = 10/(600 cat months) = 0.0167 cases/cat month IR = 10 cases/(50 cats x 52 wk) = 10/(2600 cat weeks) = 0.00385 cases/cat week Incidence rate depends on the time interval! For convenience we say, “annual incidence of FVR is 0.20 cases per cat”  Exact method for changing population In our previous examples, all individuals remained in the population at risk for the time interval over which new cases were counted Use the exact method to estimate the incidence rate if animals are continuously entering and leaving the population at risk (i.e., animal population size is changing over time interval) Divide the number of new cases over the time interval by the total number of animal time units at risk Sum time units at risk contributed by each animal. Observing 6 cows for 1 year or 1 cow for 6 years is the same Incidence rate denominator uses total number of animal time units that the animal population was at risk for the disease.  Example of exact method to estimate cow mortality rate Estimate incidence rate of death for a herd of 100 cows over a period of 12 months Over 12-month study period, 10 cows die 5 cows die after 2 months, 2 cows die after 5 months, 3 cows die after 8 months Use the exact method to calculate the mortality rate (incidence rate of death) Thus, 5, 2, 3, and 90 cows contribute 2, 5, 8, and 12 months of risk Sum of cow months of risk is 5*2 + 2*5 + 3*8 + 90*12 = 1124 cow months Incidence rate = 10 cow deaths/1124 cow months = 0.008896797 deaths per month Mortality rate is synonym for the incidence rate of death Mortality rate in cow herd is 88.97 deaths per 10,000 cow-months  Use approximate method to estimate cow mortality rate Use the approximate method to estimate the mortality rate if we don’t have exact information on when cows died Assume that 10 deaths occurred halfway through the time interval (i.e., 6 months) 90 cows x 12 months + 10 cows x 6 months = 1140 cow months Cow mortality rate is 10 deaths/1140 months = 0.00877193 deaths per month Shortcut to calculate total animal units of risk is to multiply average population size by time interval: 95 cows x 12 months = 1140 cow months Mortality rate for approximate method (87.72 deaths per 10,000 months) similar to exact method (88.97 deaths per 10,000 months) Question: Why is mortality rate higher for exact method (88.97 deaths per 10,000 months) versus approximate method (87.72 death per 10,000 months)?  Prevalence, incidence rate, and average duration of disease Relationship between the prevalence, incidence and average duration of infectious disease Epidemiologists use concept of water entering and leaving a bathtub Water in the bathtub is disease prevalence in host population Water entering bathtub are new cases of disease (incidence) Infected individuals can recover from disease (evaporation) or they can die (go out the drain) Prevalence, incidence rate, and average duration of disease If population is in a steady state (gains and losses of infected individuals are constant), the relationship between prevalence (P), incidence rate (IR), and duration of infection is as follows: P/(1 – P) = IR * Average duration of disease For diseases with a low prevalence, 1 – P ~ 1 and equation becomes P = IR * Average duration of disease If the incidence rate or average duration of disease increase, the prevalence will increase. In contrast, if incidence rate or average duration of disease decrease, the prevalence will decrease.  Change in the prevalence of HIV in Kenya HIV causes AIDS in human patients Graph shows prevalence of HIV in Kenya from 1996 to 2006. At this time, AIDS was inevitably fatal Development of anti-retroviral drugs did not cure infection, but allowed people to live longer with the infection Prevalence of HIV increased from 1990 to 2000 because the average duration of the infection increased After 2000, availability of anti-retroviral drugs decreased, mortality rate of people infected with HIV increased, and the prevalence of HIV in the population decreased  Outline of Measuring Disease Part 1 Quantify the course of infectious disease for Johne’s disease and rabies Define incubation period, latent period, illness, and infectious period Define outbreak, epidemic, pandemic, endemic Monitoring outbreak requires case definition (suspected, probable, confirmed) Monitoring outbreak requires counting cases and defining population at risk Measures of disease risk include prevalence and incidence Prevalence is the proportion of animals that have the disease at an instant in time Incidence is the number of new cases in specified time interval Incidence risk and incidence rate are used under different circumstances Exact method of calculating incidence rate sums animal time units of risk Prevalence, incidence and duration of disease are related to each other  Identifying and counting cases Case finding is critical to success of outbreak investigation Investigators need to “case find” to get the maximum amount of information early in the outbreak to better understand disease epidemiology Early detection and early intervention can prevent a larger outbreak Many cases will go undetected for a variety of reasons: (1) sick patients may not get care, (2) vets may not recognize disease, (3) not all cases will be tested An “outbreak” may occur because we do a better job of looking for or detecting cases New and improved diagnostic testing can increase the number of cases Availability of diagnostic tests can play a role How hard we look for cases can also affect case numbers  Annual counts of BRD in a feedlot Year Cases of BRD 2012 245 2013 68 2014 403 2014 358 2016 374 What inferences can we make based on these data? Are we missing any important pieces of information? What do we need to compare the risk of disease between years? Prevalence and incidence of HIV in the USA from 1980 to 2010  Approximate method to estimate the incidence rate Incidence rate = number of new cases of disease that occur in a population during a particular time interval divided by the average of the number at risk at the start and the end of the time interval This method is useful if we only determine the number of animals at risk at the start and the end of the time interval Animals leave the population of risk because they develop the disease or because they are removed from the population (natural death, disease-induced death, culling, selling) Animals enter the population of risk via births and purchases This calculation assumes that, on average, the animals will enter or leave the population halfway through the time interval  Example of approximate method to estimate the incidence rate Estimate the incidence rate of BRD in feedlot cattle over the course of 6 months Feedlot contains 300 animals at the start, 20 of them develop BRD, and 10 are removed from the pen for other reasons What is the incidence rate (IR) per month? What is the incidence rate per cow year? Population of cattle at risk at start and end of time interval are 300 and 270. Mean population at risk for 6-month time interval is 285 animals IR per month is 20 cases/(285 cattle * 6 months) = 0.0117 cases per cattle month IR per year is 20 cases/(285 cattle * 0.5 years) = 0.1403509 per cattle year Why is the incidence rate of BRD per cattle year 12x higher compared to the IR per cattle month?  Case definitions for Foot and Mouth Disease Case definitions for FMD are confirmed, presumptive, and suspect The North American Food-and-Mouth Disease Vaccine Bank (NAFMDVB) Guidelines have defined presumptive and confirmed diagnosis as a basis for communication among Mexico, Canada, and the USA Confirmed case: The FMD virus has been isolated and identified by the National Centre for Foreign Animal Disease (NCFAD); OR NCFAD has identified viral antigen or RNA specific to FMD in samples from one or more animals that are either showing clinical signs consistent with FMD or an epidemiological link to a confirmed outbreak of FMD; OR Antibodies to structural or non-structural proteins of FMDV, which are not a consequence of vaccination, have been identified by NCFAD with clinical signs consistent with FMD or an epidemiological link to a confirmed outbreak  Presumptive case of FMD Presumptive case of FMD is defined as follows Clinical signs or post-mortem lesions confirmed to be consistent with FMD have been investigated by a CFIA diagnostician or a veterinarian in charge (VIC) or a district veterinarian (DV), and determined as high risk in collaboration with the Area Food Animal Disease (FAD) program officer; AND There is an epidemiological link to other confirmed cases of FMD; OR Canadian Animal Health Surveillance Network (CAHSN) laboratory reports to National Centre for Foreign Animal Disease (NCFAD) the determination of a “non-negative” FMD result; OR Antibodies to structural or non-structural proteins of FMDV that are not a consequence of vaccination have been identified by NCFAD CFIA Operations may take action to eradicate the disease, based on a presumptive diagnosis of FMD  Suspect Case of FMD The European Union (EU) Council Directive 2003/85/EC defines “animal suspected of being contaminated” as any animal of a susceptible species which, according to the epidemiological information collected, may have been directly or indirectly exposed to the FMD virus. A suspect case is defined as follows: The presence of clinical signs or post-mortem lesions in susceptible animals consistent with FMD reported by a private practitioner, an owner, a provincial laboratory, or a veterinarian in charge (VIC) or district veterinarian (DV), and determined as high risk in collaboration with the Area FAD program officer (samples sent to the National Centre for Foreign Animal Disease, or NCFAD); OR All susceptible animals epidemiologically determined to have been exposed by direct or indirect contact to FMD virus.