Dr. Andres Perez - Spatial Epidemiology of PED Virus
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Transcript of Dr. Andres Perez - Spatial Epidemiology of PED Virus
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Andres PerezAssociate Professor, CVM, [email protected]
Spatial epidemiology of PED
2014 Allen D. Leman Swine ConferencePre-conference workshop
September 13, 2014St. Paul RiverCentre, St. Paul, Minnesota
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Introduction
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Coauthors
Julio Alvarez (DVM, PhD) Research Associate, CVM, U of MN
Dane Goede (DVM) Research Assistant, CVM, U of MN
Bob Morrison (DVM, PhD)Professor, CVM, U of MN
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Objective and methods
• To assess the spatial dynamics of PED spread in two case-studies (NC and IA)
• Techniques used– Cuzick-Edwards’ test
• Do cases tend to neighbor other cases?
– Knox / Mantel test• Do cases tend to cluster within critical times and distances?
– Directional test• Do cases spread on a given direction?
– Scan statistic• Where and when did clusters occurred?
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Results and Conclusions
We will show that:1. There were areas and times at highest risk for
disease and that disease spread on specific directions
2. Cases neighbored other cases (<20thand <4th order of neighborhood in NC and IA, respectively)
3. Clustering was maximum within 1 week, high within 2 weeks, and still significant within 3 weeks.
4. Clustering increased linearly, up to 1 mile, and then remained stable
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North Carolina
• Data from most (>70%) farms in 4 counties (>2000)– 59% finishing, 21% nursery, 15% farms with sows
• 614 positive sites (30%) (54.6% lateral)• Report of cases– Start: July-2013– End: Jan-2014
2 months
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Location and direction
• Five significant clusters:– “Early stage”– “Dissemination” stage
• Highly significant trend towards NE:33.8°
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CE: Order of neighborhood
• NC: cases largely clustered (time not considered)
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Knox test (critical time and distance)
Time (d)Space (km)
Pairs of cases
Observed-to-expected ratio
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Iowa
• Data from four companies (>400 sites)– 50% finishing, 6% nursery, 42% farms with sows
• Several counties (majority of sites there)• 156 positive sites (37%) (73% lateral)• Cases– Start: May-2013– End: Feb-2014
5 months
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• 2 significant clusters– Dissemination stage
• 8 cases in four days (0.64 expected!)
– Late stage
• Highly significant trend towards SE: 322 °
Location and direction
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• Cluster at the first levels of neighborhood (k=4)
CE: Order of neighborhood
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Knox test (critical time and distance)
Time (d)Space (km)
Observed-to-expected ratio
Pairs of cases
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Results and Conclusions
We showed that:1. There were areas and times at highest risk for
disease and that disease spread on specific directions
2. Cases neighbored other cases (<20thand <4th order of neighborhood in NC and IA, respectively)
3. Clustering was maximum within 1 week, high within 2 weeks, and still significant within 3 weeks.
4. Clustering increased linearly, up to 1 mile, and then remained stable
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Thank you!Andres Perez Associate Professor
Julio AlvarezResearch Associate
Javier SarradellVisiting Professor
Ana Alba Visiting Researcher
Barbara Brito Research Specialist
Pablo Valdes Research Specialist
Amy KinsleyResearch assistant
Gabe AlGhalithResearch assistant