Chapter 17 Risk-weighted Surveillance Quotas Model

17.1 What is the Risk-weighted Surveillance Quotas Model?

The Risk-weighted Surveillance Quotas Model incorporates risk factors for chronic wasting disease (CWD) introduction and exposure of wild deer, including anthropogenic (human-related) and demographic (deer population) forces to proportionately distribute an overall sampling point quota to sub-administrative areas.

17.2 What Questions Does the Model Answer?

Question 1. How can I identify areas with the highest risk of CWD introduction or increasing prevalence to maximize our surveillance efficiency? Cumulative risk scores incorporating identified risks associated with cervid businesses, risks from neighboring administrative areas, and deer population estimates are calculated for each sub-administrative area (e.g., county, deer management unit). Risk scores are an indication of the risk for CWD introduction or increasing prevalence associated with a sub-administrative area; the higher the number, the higher the risk.

The following risk factors are used in calculating Risk-weighted Surveillance Quotas: - Anthropogenic Risk Factors - Captive cervid facilities (e.g., cervid farms and hunting enclosures) - Taxidermists and Meat Processors - Adjacency to sub-administrative areas in which CWD has been detected - Conditions and activities of neighboring administrative areas (e.g., state, province, tribal nations) - Demographic Risk Factors - Number of deer in sub-administrative area - Number of deer in adjacent sub-administrative areas

Question 2. How do I distribute sampling effort across my jurisdiction to target areas where CWD is most likely to appear or increase in prevalence? The administrative area-wide sampling point quota, as provided by the user, is distributed proportionately per sub-administrative area based on the risk scores. You assign the appropriate surveillance category (see Table 1 below) to each sub-administrative area according to CWD status and other risk factors. The model proportionately distributes the total sampling point quota across areas designated as “early detection” based on risk scores. You choose the level of sampling (i.e., number of points) for areas designated as “monitoring” and “high risk”.

Question 3. How do surveillance points convert to the number of deer my team needs to sample? Surveillance points per sub-administrative area can be used by agencies to determine their surveillance plans. Points, rather than counts of deer, can be used in a weighted surveillance method to focus sampling efforts on sex and age classes in which CWD is most likely to be detected. You can select your own risk weights in the Annual Surveillance Collection to guide your surveillance efforts.

17.3 Output Details

Comparative maps, data charts, and tables of the following outputs by sub-administrative area may be viewed on the Visualization page. In addition, the model execution page allows you to download your tabular outputs as .csv or .json files.

  • Surveillance category
  • Number of captive cervid facilities used in the model: obtained from the Cervid Facility data collection
  • Captive cervid facilities risk score
  • Number of meat processors used in the model: obtained from the Processor data collection
  • Number of taxidermists used in the model: obtained from the Processor data collection
  • Meat processor/taxidermist risk score
  • Adjacent state risk score
  • Anthropogenic risk score: the sum of the risk scores for captive cervid facilities, meat processors/taxidermists, and adjacent administrative areas
  • Demographic risk score: derived from the metric selected to estimate cervid population

17.4 Abbreviated Tutorial

Demography data, used as an estimate of the number of deer in each sub-administrative area, are required to calculate the surveillance quotas.

For best results, the following data should be entered into the Warehouse as completely as possible:

  • Cervid Facilities (e.g., cervid farms and hunting enclosures) data, including location, activities, and practices
  • Taxidermist and Meat Processor data, including location, activities, and practices
  1. Enter basic information to identify model run.
  2. Enter parameters, as detailed below.
  3. If desired, create Visualization associated with model run.
  4. If desired, use the model results in an Annual Surveillance Collection entry in combination with a chosen weighting scheme.

17.5 Parameters Needed to Execute the Model

  • Reference name (Required): Enter a name to help you identify your model run for future reference. Note that this field does not affect the model run.
  • Applicable season year (Optional): Select the season year (for your reference) from the drop-down list. Note that this field does not affect the model run.
  • Notes (Optional): Enter any notes about the model run details. Note that this field does not affect the model run.

To enable the Risk-weighted Surveillance Quotas Model to give you the most useful results, it is important to enter as much information as you can. When you have entered the information once, the model execution page will remember your answers, allowing you to simply edit things that have changed when you wish to run the model again.

17.5.1 Risk scoring

  • Cervid facility types of concern: Select one or more type(s) of cervid facility from the drop-down list to include as risk factor(s) in the model. The drop-down list will include all cervid facility types you have previously created when importing/entering your cervid facility data into the Warehouse. You can select the facility type(s) that you think present a risk for CWD introduction. For example, you may wish to include cervid farms and backyard farms, but leave out zoos, because they typically have more secure enclosures. Note: You are not required to select any cervid facility type(s). However, if you do not select any, cervid facilities will not contribute to risk scores in the model output. Cervid Facilities that have a Current Status of “Open” or “Unknown” will be included in the analysis. Cervid Facilities with a Current Status of “Closed” will not be included.

  • Risk score value (Required): Enter a value to adjust the weight of risk factors associated with conditions and activities (e.g., importation of live cervids) of neighboring administrative areas. Risk scores of neighboring administrative areas will be multiplied by the value entered to scale up (or down) risks relative to other hazard risks (e.g., cervid facilities) within the sub-administrative area adjacent to neighboring administrative areas. The higher the value, the more weight will be given to sub-administrative areas adjacent to neighboring states when determining risk scores. The default value of 15 is a suggested starting point. Note: This number can be any positive number, including 0. Be aware that values <1 will decrease the weight of risk factors associated with neighboring administrative areas and 0 will exclude them.

  • Adjacent to cwd unit (Required): Enter a value to be added to the risk score for sub-administrative areas adjacent to high risk or monitoring sub-administrative areas (see Table 1 for definitions). This step provides an opportunity for agencies to increase the risk score of sub-administrative areas that are one area away from CWD+ areas or other high-risk areas. This value may be any positive number, including 0. The default value of 100 is a suggested starting point.

  • Demographic data (Required): Select the season-year and type of demographic data (e.g., total harvest or population) from the drop-down list that you want to use to estimate deer numbers in a sub-administrative area. All demographic data you have uploaded into the Warehouse will be available to choose from. Note: The first option in the drop-down list will be selected by default if nothing is selected.

17.5.2 Surveillance quota determination

  • Surveillance point total (Required): Enter your total surveillance point goal for administrative area-wide early detection sampling for the season-year. Keep in mind this total does not apply to any high risk or monitoring sub-administrative areas; additional points, set by you, for these areas will be added to this total after the model has run. The value of the surveillance point total will determine the confidence level for detection of CWD. For example, to allow detection of at least one case of CWD with 95% confidence if the prevalence in yearling males (the reference class for comparison) is 1%, the administrative area-wide sampling quota should be set at 2,994 points. For simplicity, this value can be rounded up to 3,000 points.

  • Anthropogenic hazard allocation (Required): Enter the proportion (a decimal number between 0 and 1) of the Surveillance point total to be allocated to sub-administrative areas based on anthropogenic risk scores. The remaining proportion will be allocated automatically to demographic risk scores of sub-administrative areas.

  • Monitoring zone point quota (Required): Set the point quota to be assigned to sub-administrative area(s) designated as “Monitoring”. Monitoring zones typically include sub-administrative areas that already have CWD. Note: Sub-administrative areas designated as “Monitoring” are not included in the distribution of the Surveillance point total based on anthropogenic and demographic risk scores. The additional points for these areas will be added to the total point quota after running the model. If you do not have any sub-administrative areas designated as Monitoring, you can set this value to zero.

  • High risk zone point quota (Required): Set the point quota to be assigned to sub-administrative area(s) designated as “High Risk”. High risk zones typically include sub-administrative areas that are adjacent to CWD+ areas or are otherwise of extra concern to wildlife managers. Note: Sub-administrative areas designated as “High Risk” are not included in the allocation of the Surveillance point total based on anthropogenic and demographic risk scores. The additional points for these areas will be added to the total point quota after running the model. If you do not have any sub-administrative areas designated as High Risk, you can set this value to zero.

17.5.3 Surveillance categories

Select the surveillance category for each sub-administrative area using the drop-down list next to each area name. The categories include monitoring, high risk, and early detection, and are defined in Table 1.

Table 1. Surveillance categories that may be assigned to sub-administrative areas to calculate point quotas.

Surveillance category CWD status Goal Point quota
monitoring CWD is present Monitoring spread and change in prevalence of CWD Determined by agency
high risk CWD has not been detected in sub- administrative area but the area is adjacent to an area with CWD or is of extra concern to wildlife managers Detection of new outbreaks of CWD resulting from natural movement of infected deer from neighboring areas Determined by agency
early detection CWD has not been detected in sub- administrative area or neighboring areas Detection of new outbreaks of CWD from unknown or long-distance sources Proportional allocation based on the accumulation of hazards and deer density

Note: The model will default to “early detection” for any sub-administrative area that is not marked as “monitoring” or “high risk”. Please ensure that all monitoring and high risk areas are appropriately tagged.

17.6 How the Model Works

The Risk-weighted Surveillance Quotas Model is a deterministic series of mathematical equations that come together to calculate anthropogenic and demographic risk scores for each sub-administrative area in your jurisdiction. Data indicating the location, activities, and practices of cervid facilities, taxidermists, and meat processors are used to aggregate potential hazards for each sub-administrative area. Data on the activities and conditions in neighboring administrative areas are used to assign additional risks to sub-administrative areas bordering other administrative areas. Demographic data on deer population is used to quantify the risk associated with the estimated deer population in an area. Expert opinion surveys, where available, are used to appropriately weight these hazards in your jurisdiction. Where they are not available, an average of all expert opinion survey results is used for hazard weights. Risk scores are totaled for each early detection sub-administrative area and the Surveillance point total is proportionately allocated to sub-administrative areas in the early detection category. Specified points are assigned separately to high risk and monitoring sub-administrative units.

The following notation is used:

Cervid Facilities
C Cervid facility
FL Fencing quality low
FM Fencing quality medium
FH Fencing quality high
SS CWD-susceptible species raised in facility
NC Non-compliant owner of facility
IO Cervid importation from out of state
DR Disposal risk (uses a risky method of parts disposal)
SO Shooting operation
DRe Also a deer rehabilitator
DP Also a deer processor
DT Also a deer taxidermist
Processors and Taxidermists
T Taxidermist
P Processor
HP 100+ animals processed per year
TP 10-99 animals processed per year
TL Fewer than 10 animals processed per year
IR Imports carcasses/parts from out of state
DRe Also a deer rehabilitator
CC Also a captive cervid facility
DR Disposal risk (uses a risky method of parts disposal)
Adjacent State
A Adjacent state
PO CWD in wild deer (1=detected, 0=not detected)
WS Wildlife surveillance program size (1=less than 1000, 0.5=10005000, 0=greater than 5000)
CF Captive cervid facilities (1=allowed, 0.5=restricted, 0=prohibited)
LI Importation of live cervids (1=allowed, 0.5=restricted, 0=prohibited)
HF High fence shooting operations (1=allowed, 0.5=restricted, 0=prohibited)
OV Unregulated captive cervid activities (1=present, 0=absent)
TP Unregulated taxidermists and processor activities (1=present, 0=absent)
SN Unregulated sovereign nation (1=present, 0=absent)
Miscellaneous
EW Expert weight for hazard (determined by expert risk survey responses)
ED Extra points allocated for adjacency to high risk or monitoring units (determined by user)
D Deer population of unit (determined by selected demographic data)
N Deer population of adjacent high risk or monitoring units

Anthropogenic and demographic quotas are determined separately by taking out any high risk or monitoring surveillance units, using the number of points given to each hazard type, and allocating them proportionally to each hazard type for each unit.

Total quotas for each unit are the sum of anthropogenic and demographic quotas for early detection units and the pre-determined point number for high risk and monitoring units.

17.7 Details on the Theory

Schuler KL, Hollingshead NA, Heerkens S, Kelly JD, Hurst J, Abbott RC, Hanley BJ, Collins E, Hynes KP. A “hazard model” using risk-weighted surveillance for first detection of chronic wasting disease. In preparation.