Lecture 18 - Measuring Disease Part 3 PDF

Measuring disease – Part 3 Time = 8:30 AM  Outline of Measuring Disease Part 3 Define animal disease surveillance Mandatory surveillance of reportable animal diseases include exotics and endemics Purpose of disease surveillance differs between exotic versus...

Measuring disease – Part 3 Time = 8:30 AM  Outline of Measuring Disease Part 3 Define animal disease surveillance Mandatory surveillance of reportable animal diseases include exotics and endemics Purpose of disease surveillance differs between exotic versus endemic diseases Demonstration of freedom from disease important for trade access Characteristics of surveillance: time, coverage, representation, sensitivity and specificity Passive surveillance versus active surveillance (e.g., eTick versus field sampling ticks) Use of databases in veterinary clinics or diagnostic labs for research Chain of steps that influence sample submission to a diagnostic lab Sub-types of active surveillance: targeted, sentinel, abattoir  Animal health surveillance identifies important disease events (incursions, Define outbreaks, emergences) in animal populations allowing farmers, veterinarians and government agencies to develop timely animal and appropriate responses aimed at eradicating, controlling or mitigating the adverse effects of these diseases. disease World Health Organization (WHO) defines surveillance as ‘the ongoing systematic collection, collation, analysis and surveillance interpretation of data and the dissemination of information to those who need to know in order for action to be taken’ (World Health Organization 2001).  Disease surveillance systems have two components, detection and response Detection is the monitoring system used to detect or Detection monitor disease and Response is a defined set of interventions that will take place if the disease reaches a threshold prevalence in the animal population Response Types of monitoring systems, types of interventions, disease threshold that triggers a response vary greatly among different animal diseases Surveillance is expensive. We prioritize animal diseases that affect public health or the economy  Reportable diseases of terrestrial animals in Canada Reportable diseases of terrestrial animals can impact human health, animal health and Canadian economy Animal owners, veterinarians and labs must report suspect cases of these diseases to CFIA district veterinarian CFIA maintains records of the incidence of these reportable diseases in Canada, which is surveillance Question: What types of hosts are affected? What are the priorities of the CFIA?  Reportable diseases affect livestock and humans Question: What types of host animals are affected? 31 reportable diseases: 20 diseases of livestock (cattle, pigs, sheep, goats), 5 of horses, 4 of birds, and 2 of wildlife 11 are zoonotic, 5 are low risk zoonotic (or uncertain), and 15 are NOT zoonotic No reportable diseases exclusive to companion animals (rabies can occur in pets, but also humans and wildlife) Priorities are public health and Canadian economy Exotic, sporadic, and endemic reportable diseases Reportable diseases are dominated by exotic (non- endemic) diseases that Canada wants to keep out 19 of 31 reportable diseases are exotic (i.e., are not present in Canada) 7 reportable diseases have sporadic outbreaks in Canadian poultry and livestock (bluetongue, equine infectious anemia, fowl typhoid, pullorum disease, scrapie, trichinosis) Remaining 5 reportable diseases are endemic in wildlife (avian influenza, bovine tuberculosis, chronic wasting disease, Newcastle disease, rabies) Question: Why are common and economically important diseases of livestock, such as BRD, Johne’s disease, swine influenza not reportable diseases?  Purpose of disease surveillance Purpose of surveillance differs between non-endemic (exotic) and endemic diseases Non-endemic or exotic diseases are not usually present in Canada Endemic diseases are present or endemic in Canada. These diseases are not necessarily common For non-endemic (exotic) diseases in Canada Early detection of disease (exotic, non-endemic) Demonstrating freedom from disease (exotic, non-endemic) For endemic diseases in Canada Measuring the level of disease (endemic) Finding cases of disease (endemic) Time = 8:40 AM  1) Trade access – ability to export animals or animal products 2) Trade barriers – countries with demonstrated freedom can prevent Demonstration imports of freedom 3) Stopping control or eradication measures that have been in place 4) Removing public health measures with demonstrated freedom from zoonotic disease  Demonstration of freedom – Trade access Canada is free from many infectious diseases of livestock Freedom from disease gives Canada trade access to other countries Canada exports animal products to countries around the world 70% of Canada’s pork is exported In 2019, Canada exported 1.2 million tonnes of pork with a value of $4.2 billion CAD  Demonstration of freedom – Erect trade barriers Freedom from disease allows countries to erect trade barriers against other countries World Trade Organization developed the Sanitary and Phytosanitary Measures (SPS) in 1995 SPS sets rules for food safety and animal and plant health World Organisation for Animal Health (WOAH) creates list of important animal diseases Example, foot-and-mouth disease (FMD) is on the WOAH list. Countries free from FMD can refuse animal products from countries not free from FMD If two countries have same animal disease, they cannot erect trade barriers against each other  WOAH map of classical swine fever status WOAH monitors disease-free status of member stats Map shows countries that are free from classical swine fever (green) Canada and USA are free from CSF, whereas Africa and most of Asia are not Canada can erect pork trade barriers against most of the world Canada imports meat from only 16 of 195 countries  Stopping control measures that have been in place Countries lose disease-free status following outbreak Countries must demonstrate freedom from disease to regain disease-free status from WOAH. This requires costly surveillance and eradication efforts In May 2003, cattle with BSE detected in Canada. Canada lost BSE-free status, USA, Mexico, and Japan erected trade barriers. Canada lost $4.2 billion CAD in trade from May 2003 to Sept 2007 Canada implemented costly surveillance program to detect and eradicate BSE-infected cattle to convince trading partners its beef was safe to eat In July 2005, USA ended ban on importation of live Canadian cattle. In 2019, Japan lifted ban on import of Canadian beef from cattle older than 30 months In 2021, WOAH reinstated Canada’s BSE-free status. Canada can reduce its BSE surveillance program  Characteristics of surveillance programs Characteristics include time component, population coverage, representativeness of host population, sensitivity and specificity Time component – surveillance can be continuous, periodic, or intermittent Population coverage – proportion of population sampled Representativeness – members of the host population are targeted (representative or risk-based) Sensitivity and specificity of disease detection method Purpose of surveillance determines the characteristics of program Surveillance is time-consuming and expensive. Incentive to do minimum effort necessary to meet surveillance objectives Time = 8:50 AM  Purpose and characteristics of surveillance programs Early detection Demonstration of Measuring endemic Case finding (to (at the border) freedom (for trade) disease eradicate disease) Continuous (or Periodic or Periodic or Time component Continuous periodic for slow intermittent intermittent diseases) Comprehensive/ Population coverage Comprehensive Sample Sample Sample Use risk-based Representativeness Entire population is Random and sampling to increase Risk-based (sample type) sampled representative sample efficiency Good sensitivity and Increase specificity at High sensitivity to High sensitivity to good specificity expense of sensitivity Sensitivity and find cases (minimize find cases (minimize (don’t want to raise (be confident that a specificity of test false negatives, false false negatives, false false alarm with false case is disease of positives OK) positives OK) positives) interest)  Surveillance for exotic disease in imported horses CFIA conducts continuous, comprehensive surveillance of exotic diseases in horses imported into Canada. Horses imported into Canada must be free of 6 diseases: African horse sickness, Dourine, Glanders, Venezuelan equine encephalomyelitis, equine piroplasmosis (EP), and equine infectious anemia (EIA) Prior to import, horses from European Union (EU) must be quarantined for period of 90 days. This quarantine will allow horses to clear most infections Following entry into Canada, horses are quarantined again and must be tested for Glanders, equine piroplasmosis (EP), and equine infectious anemia (EIA) All horses imported into Canada from EU must go through this double quarantine  Demonstration of freedom of disease in Canadian pigs CFIA conducts periodic sampling at abattoirs to demonstrate freedom of exotic disease in Canadian pigs Test for 3 reportable exotic diseases: porcine brucellosis, trichinosis, and pseudorabies Not necessary to test pig population every year to demonstrate freedom from disease Canada has a population of 14.5 million pigs. Complete coverage is not possible. CFIA collects blood from random sample of mature pigs at Canadian slaughter facilities. Conducts serological testing of blood for 3 diseases Surveys have always demonstrated that pig populations in Canada are free of these 3 diseases  Surveillance of sporadic or endemic diseases in Canada Reportable diseases can be sporadic in farm animals and/or endemic in wildlife Sporadic diseases are associated with backyard farming operations and include trichinosis in swine, fowl typhoid and pullorum disease in chickens Endemic wildlife diseases include avian influenza, bovine tuberculosis (BTB), chronic wasting disease, and rabies Mandatory reporting allows CFIA to monitor incidence of endemic diseases in animal populations over time, and respond if necessary CFIA responded to repeated outbreaks of BTB in elk in Riding Mountain National Park, Manitoba (1991 to 2003) Surveillance of avian influenza (wild birds) screens for subtypes infectious to humans  Passive versus active surveillance Passive surveillance relies on disease reports by various actors (producers, vets, labs, abattoirs, members of public) that are collected by another actor (veterinary authorities, diagnostic labs) Passive surveillance often uses data that were collected for other reasons. For example, veterinary clinical records could be used to study incidence of disease Active surveillance is the purposeful collection of data to obtain information on a specific disease in an animal population Passive surveillance detects animals with clinical signs (tip of the iceberg). Active surveillance samples diseased, asymptomatic, and healthy individuals (entire iceberg) Passive surveillance data is collected haphazardly and is therefore always biased. The purpose of active surveillance is to obtain unbiased, representative data Passive surveillance is initiated by observers whereas active surveillance is initiated by investigators (or scientists) Active surveillance is much more costly and time-consuming than passive surveillance. Governments like passive surveillance because it’s cheap Question: Why do passive surveillance systems produce biased data?  Example of eTick (www.etick.ca) eTick is a website that allows users to submit photos of ticks that bit them or their pets Users submit data on date and location of tick bite encounter and who get bit (person, pet) eTick provides user with identification of tick species, and information on risk of TBD Example of citizen science. Users provide platform with data on where they encountered ticks Example of passive surveillance. Data collection is initiated by users. Data is biased Question: How is data biased? Time = 9:00 AM Map of eTick submissions in Saskatchewan Use presence/absence and abundance data on ticks to determine their ecological niche Determine how climate change will influence the distribution and range of a tick species Map shows where people were bitten by American dog ticks (Dermacentor variabilis) in the lower half of Saskatchewan Question: Where do most of the American dog ticks occur on this map? Question: What is the bias in these data for estimating the ecological preferences of ticks? Active surveillance for ticks Active surveillance = select sites and collect ticks Investigator decides what sites will be selected Sites could be selected at random, maximize coverage of the province, or stratified by biogeographic zones Flagging is classic method to sample ticks in field. Walk a transect and drag a cloth behind you Flag mimics moving animal. Ticks will attach to the flag. Count ticks at end of transect Estimate density of ticks by dividing tick count by surface area of the drag Active surveillance allows you to determine distribution and abundance of ticks in Saskatchewan  Distribution of Dermacentor andersoni in southern Alberta Map shows distribution of Rocky Mountain wood tick (Dermacentor andersoni) in grasslands of southern Alberta Study sampled 86 sites that covered the area of interest and collected ticks using the flagging method Black symbols indicate where ticks were detected. White symbols indicate where ticks were not detected Colors predict probability of encountering D. andersoni; high in read areas and low in blue areas For passive surveillance, absence of submissions (white symbols) could mean no ticks and/or no people Active surveillance: areas with tick and areas with no ticks (whole iceberg). Passive surveillance: areas with people and ticks (tip of iceberg)  Prairie Diagnostic Services Prairie Diagnostic Services (PDS) provides veterinary diagnostic services for their clients Cattle: BCoV, BPI3, BVDV, MAP, Mycoplasma bovis Canine: Brucella, Canine distemper virus, Leptospira, Rabies, Tick panel (Babesia, Anaplasma, Borrelia, Ehrlichia), and Toxoplasma Porcine: Brachyspira, Porcine circovirus, porcine corona panel, porcine diarrhea panel, PRRS, swine influenza PDS records test results in database. Use database to determine prevalence or incidence of infectious diseases in animal species of interest Question: Is using the PDS database for surveillance an example of passive or active surveillance?  Clinic is not representative of the general population Most animals in a veterinary clinic are sick. Most samples submitted to a diagnostic lab are from sick animals Animals at a veterinary clinic or a diagnostic lab are not representative of the general population Clinics and diagnostic labs are counting cases of disease, but we have no idea of the population at risk (i.e., denominator) Question: Is the number of infected animals (i.e., numerator) at least reliable? Question: Are all producers and pet owners equally likely to spot infectious disease in their animals and contact a veterinarian? Question: Are all veterinarians the same? Will they submit samples from all diseased animals or a subset of diseased animals? Chain of steps that influence sample submission 9:10 AM Infected animal Producer Producer consults shows clinical sign recognizes that veterinarian of disease animal is sick Samples submitted Veterinarian Appropriate tests to diagnostic examines animal conducted to laboratory (e.g., and takes samples detect disease PDS) Question: How do we reduce this variation in the reporting of reportable diseases?  Passive versus active surveillance Passive Active Reports of diseased animals Surveillance of disease in animal Purpose (tip of iceberg) population (whole iceberg) Population at risk Targeted by Little or no information (denominator) surveillance program Representative of Never representative Aims to be representative population of interest (always biased) Accuracy of disease Low Better prevalence estimates Led by Observers Investigators Record keeping is done Expensive and Cost and effort for other reasons time consuming Sub-types of active surveillance: targeted, sentinel, abattoir  Targeted or risk-based surveillance Targeted or risk-based surveillance selects animals with highest risk of having the disease of interest Targeted surveillance used for early detection, demonstrating freedom from disease, and case finding to eradicate disease Targeted surveillance optimizes limited resources (time, money) Canada used risk-based surveillance for bovine spongiform encephalopathy (BSE) Target cattle that are diseased, down, dying, or dead (4D). These animals are at high risk of BSE BSE is rare in Canada. From 2004 to 2023, 670,411 brain samples tested and 19 cases of BSE detected Random sampling of animals would be very inefficient for detecting BSE in cattle  Sentinel surveillance Canary in the coal mine. Miners brought canaries into the coal mine to detect poisonous gasses Sentinel mice are kept in animal care units with experimental mice. Sentinel mice tested for panel of mouse pathogens Rare vector-borne pathogens (e.g., Powassan fever virus) have low prevalence in vectors (< 1%), but higher seroprevalence in vertebrate host Test animal reservoirs where pathogen has high abundance in tissues increasing detectability (type of targeted or risk-based surveillance) Emilia-Romagna region in Italy screens corvids (magpies, crows, jays) for WNFV WNFV was detected 3 weeks earlier in corvids compared to humans. Thus, surveillance of corvids is an early warning system  Abattoir surveillance African swine fever (ASF) is highly infectious viral disease of pigs with high case fatality rate No vaccines or treatments currently available. ASFV is not zoonotic; no health risks to humans China has herd of 450 million pigs and accounts for 45% of global pork production Outbreak of ASF in China led to culling of millions of pigs and economic losses of $111 billion USD Canadian pork industry is very concerned about ASF, which is an exotic and reportable disease CanSpotASF is a national surveillance system for early detection of ASF in swine in Canada In April 2022, included risk-based detection testing of condemned carcasses at abattoirs  Targeted surveillance and eradication In 1950s, estimated 50 million cases of smallpox worldwide, 2 million deaths per year In 1967, WHO began 10-year smallpox eradication campaign in Africa and Indian subcontinent Officials had to find cases (surveillance) followed by ring vaccination where all close contacts of the patient were immunized with smallpox vaccine Public health agencies in developing countries were often not reliable in reporting smallpox cases Dr Nicole Grasset initiated the smallpox recognition card (photo of a smallpox-infected child) Smallpox symptoms were highly recognizable by lay people and led to efficient case finding (surveillance) Dr Nicole Grasset Last case of smallpox detected in Somalia in 1977 Time = 9:20 AM  Summary of Measuring Disease Part 3 Define animal disease surveillance Mandatory surveillance of reportable animal diseases include exotics and endemics Purpose of disease surveillance differs between exotic versus endemic diseases Demonstration of freedom from disease important for trade access Characteristics of surveillance programs: time, coverage, sensitivity and specificity Passive surveillance versus active surveillance (e.g., eTick versus field sampling ticks) Databases in veterinary clinics or diagnostic labs are passive surveillance Chain of steps that influence sample submission Sub-types of active surveillance: targeted, sentinel, abattoir End of course # 18  Sensitivity and specificity Sensitivity and specificity are two measures that determine the quality of a diagnostic test. Both are measured as a percent Sensitivity is the probability of obtaining a positive result for the subset of infected individuals. Sensitivity = true positives/(true positives + false negatives) Specificity is the probability of obtaining a negative result for the subset of uninfected individuals. Sensitivity = true negative/(true negative + false positive) If the sensitivity is high, the probability of false negatives is low. Advantage: Confident that you are not missing truly infected cases. Disadvantage: Higher probability of false positives (more false alarms) If the specificity is high, the probability of false positives is low. Advantage: Confident that a positive test is truly infected (no false alarms). Disadvantage: Higher probability of false negatives (missing truly infected cases)  Disease surveillance in imported cattle from USA Surveillance for diseases in animals imported into Canada is continuous Population coverage depends on type of animal Cattle imported from USA for breeding purposes must be free from brucellosis Feeder cattle imported from USA are not tested for infectious diseases. Too time-consuming and expensive List of requirements to ensure that feeder cattle are healthy before and after their journey from USA to Canada