Investigation of land coverage and elevation as risk factors for

PRRS breaks

Andreia Arruda, DVM PhDUniversity of Minnesota

BackgroundCumulative PRRS incidence 2009-2017 (SHMP)

Background

Background

Background

Background

Objective

Investigate whether land elevation and coverage are associated with PRRS breaks

- Account for important factors of interest

- Use data from swine sites spread across the country

Methods

Data source: SHMP (n=706 sow herds), 2009-2016

Variables of interest: • Terrain elevation• Land coverage• Swine density• Geographical region• Herd size

MethodsDensity of swine sites participating in the SHMP

MethodsDensity of swine sites (FAO, modelled; 2005)

Elevation• The height of a terrain

– Absolute number – altitude (meters above sea level)– Relative number – slope, steepness as compared to

other features in the area

runrise

Slope = riserun

e.g. 20 𝑓𝑓𝑓𝑓100 𝑓𝑓𝑓𝑓

= 0.2 or 20%

86m

80m86m

1m = 3.3 ft

12345

SlopePublished 2007-02-16NASA Shuttle Radar Topographic Mission (SRTM), 2006USGS Geological Survey (GTOPO30), 2002

1- 2% (8%)2-5% (35%)5-8% (43%)8-16% (10%)16-30% (5%)30-45% (0)> 45% (0)

AltitudeThe CGIAR Consortium for Spatial InformationNASA Shuttle Radar Topographic Mission (SRTM), 2006USGS Geological Survey (GTOPO30), 2002

1: <185m (25%) 2: 185 - 316m (25%)3: 317 - 391m (25%)4: > 391m (25%)

Land Coverage Joint Research Centre (European Commission)Global Land Cover 2000 Project (GLC2000)

1: cultivated and managed areas (67%)2: shrubs/ herbaceous cover (e.g. pasture) & others (14%)3: tree cover, needle-leaved or mixed (9%)4: tree cover, deciduous broad-leaved (11%)

Methods

Outcome of interest: number of breaks

Statistical model: Multilevel mixed-effects Poisson regression

• Backwards stepwise approach• Random effect for production system• Statistical significance declared at P < 0.05

Results

• Mean 1.4 outbreaks per year per site• 40% farms never reported a break

Variable¶ IRR P-value

Density 1.46 <0.001*

N animals 1.30 0.001*

Land coverage Shrubs, herbaceous 0.70 0.04*

Needle-leaved trees 0.56 0.003*

Broad-leaved trees 0.42 0.009*

Slope 2-4% 1.01 0.95

5-8% 0.77 0.10

9-16% 0.44 0.001*

17-30% 0.18 0.006*

Region MN/IA 1.59 0.001*

NC 0.83 0.60

NE 0.70 0.06

Other 0.49 0.001*

OK 1.28 0.38

PA 0.58 0.36

Results

¶Refs- low density, low N animals, land coverage as cultivated/ managed areas, slope 1% or <, region IL

Results should be interpreted with

caution due to the cross-sectional

nature of the data

• Large number farms across many US regions

• Land inclination– Airborne transmission– Proxy for other factors

• Vegetative filters

Discussion

Take-home messages

- We investigated whether land elevation and coverage are associated with PRRS breaks.- “Highly inclined terrains” were associated with

fewer breaks- Presence of shrubs and trees were associated with

fewer breaks compared to cultivated areas

Acknowledgements

University of Minnesota, College of Veterinary MedicineB. Morrison, C. Vilalta, A. PerezSHICSHMPSwine veterinarians and producers that share data

Thank you!arrud002@umn.edu