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Ranavirus Surveillance Methods
- 1. Designing Ranavirus Surveillance Studies University of Tennessee Center for Wildlife Health Department of Forestry, Wildlife and Fisheries Matthew J. Gray
- 2. Outline III.Amphibian Surveillance Example • Importance of “Aseptic” Sampling I. Uses and Biases of Surveillance Data • What are the limitations? I. Sample Design and Required Sample Size IV. Disinfecting Procedures Part One Part Two Part Three
- 3. Goal of Surveillance To detect a pathogen/disease or obtain an unbiased estimate of pathogen/disease prevalence (or incidence) in a population Pathogen Prevalence An estimate of the proportion of individuals in a population that are infected with a pathogen Infection Disease Challenge Studies: Background Levels Incidence
- 4. Detection Biases Dead vs. Morbid vs. Health Vegetation Water Depth Seasonality Sample Frequency?
- 5. Uses of Surveillance Data Occurrence and Distribution Evidence of Emergence Pathogen or disease that is increasing in distribution, prevalence, or host range Baseline http://www.bd-maps.net/
- 6. Uses of Surveillance Data Evidence of Hotspots Identification of Mechanisms of Emergence Elevated? $$ Population Effects?
- 7. Uses of Surveillance Data Disease Intervention Strategies 1. Transmission: DD 2. Distribution expansion 3. Stressors Interrupt Host-Pathogen Cycle Reduce Stressors OIE: Routes of Entry 4. Novel (Introduced) Isolate
- 8. Surveillance Designs Random Sampling All individuals or surveillance locations have an equal probability of being sampled Random Numbers Table or Programs Collecting Unbiased, Representative Sample 1) Sample all captured individuals 2) Sample up to n captured individuals 3) Randomly select individuals from sample of n captured individuals Avoid Systematic or Haphazard Sampling Objective?
- 9. Detect a Pathogen Estimating Required Sample Size •Assumed Pathogen Prevalence Level (APPL) •Estimated Host Population Size •Confidence in detection (95%) Information Needed 50 100 250 500 2000 >100,000 20 23 25 26 27 30 35 45 50 55 60 60 50 75 110 130 145 150 Population Size 10% APPL 5% APPL 2% APPL (Amos 1985, Thoesen 1994) epiR (epi.detectsize)
- 10. Precise Estimate of Prevalence Estimating Required Sample Size n p p d = − ( ) . 1 1 9 6 2 Prevalence from a previous study d = error in estimation Zα/2 =1.96 (95% confidence) p = “Error in Estimation” is the amount of error you are willing to tolerate in your estimate of prevalence p = 85% Error = 5% n = ≈( . ) ( . ) ( . ) . 0 8 5 0 1 5 1 9 6 0 0 5 1 9 6 2 p = 85% Error = 10% p = unknown Error = 10% n = ≈( . ) ( . ) ( . ) . 0 8 5 0 1 5 1 9 6 0 1 0 4 9 2 n = ≈( . ) ( . ) . 0 2 5 1 9 6 0 1 0 9 6 2 What happens if estimation error increases? What happens if prevalence is near 0.5? 0.01< P(1-p) < 0.25 Two Proportions
- 11. Wildlife Surveillance: An Amphibian (Ranavirus) Example University of Tennessee 1 Center for Wildlife Health 2 CVM Department of Pathobiology Matthew J. Gray1 and Debra L. Miller1,2
- 12. Enclosure (Pipe) Sampling Count Number of Dips Dip until No Larvae Captured after 10 dips Is probability of transmission affected?
- 13. Co-housing Animals Mean = 0.8 – 0.9 contacts/min for 40 tadpoles/m2 (10 tadpoles per 5-gal [19 L] bucket) Uniform Contact = 9 Minutes 10, 20, 40% X 15, 30, 60 min What about gloves? Ranavirus Example
- 14. Holding Containers One Individual per Container Plastic Bags 1-L or 2-L Plastic Tubs Mason Jars
- 15. Area Searches Search under Cover Objects Record Time and Observers: CPU Return to Approximate Capture Location
- 16. Aseptic Processing Station People that collect do NOT process!!
- 17. Aseptic Processing Station Station 1 ID Rinsed & Labeled
- 18. Weigh SVL Aseptic Processing Station Station 2
- 20. Tail Clip Data Recording Aseptic Processing Station Stations 4 and 5
- 21. Aseptic Processing Station Sample Storage 90% EtOH or Dry Ice
- 22. Aseptic Processing Station Station 6 Releasing or Collecting Individuals
- 24. Take the Opportunity to Instruct
- 26. Matt Gray, Debra Miller, and Amanda Duffus Diseases, Pathogens and Parasites Task Team Biosecurity Precautions: Disinfecting Procedures
- 27. Wear Disposable Gloves Gloves Rinsed with Distilled H2O Greer et al. (2009) Latex Vinyl Nitrile $12/box of 100
- 28. Disinfecting Equipment Scrape Mud and Scrub
- 29. Disinfecting Equipment Spray Bottle or Immersion •Bleach >4% •EtOH >70% •Virkon >1% •Nolvasan >0.75% Johnson et al. (2003), Bryan et al. (2009), Gold et al. (2013) $50/ bottle
- 30. Amphibian Biosecurity References www.separc.org Dodd, C. K., editor. 2009. Amphibian Ecology and Conservation: A handbook of techniques. Oxford University Press, UK. ISBN 9780199541188 Pessier, A.P. and J.R. Mendelson (eds.). 2010. Miller et al. (2015)
- 31. Questions?? Gray: mgray11@utk.edu Miller: dmille42@utk.edu Duffus: aduffus@gordonstate.edu