SHIC Sponsored Research Develops System to Help Farms Strategically Target Disease Monitoring and Control

May 15, 2018 — Paul Sundberg

The frequency of swine movement in North America makes the industry vulnerable to disease spread. To explore how modifying movement patterns can reduce disease spread, the Swine Health Information Center (SHIC) recently sponsored research at the University of Minnesota (UMN) Department of Veterinary Population Medicine. The project looked at the question: Can we reduce the vulnerability of the US swine industry to disease spread by prioritizing surveillance and control on specific farms? The answer is yes.

The research was conducted by Kim VanderWaal, PhD, Amy Kinsley, PhD candidate, Andres Perez, DVM, PhD, and Meggan Craft, PhD, from UMN. The full study along with more information about analysis of pig movement data is awaiting publication in Preventative Veterinary Medicine.

Key Take Home Messages for Swine Veterinarians

• When controlling disease spread, it is possible to calculate the ideal places in a system to start control strategies to more efficiently slow disease spread.
• These same calculations can help target the ideal locations for disease monitoring in a system.

Using SHIC support, the UMN team analyzed detailed swine movement data in three large production systems to measure the influence a specific farm has on disease spread throughout the system, which they quantified using several metrics. Specifically, they calculated:

1. the number of other farms to which a specific farm sent or received pigs
2. the Mean Infection Potential (MIP) which measures potential incoming and outgoing infection chains (i.e., chains of farms that are connected to one another via movements)

The study found directing disease interventions towards farms based on their MIP can substantially reduce the potential for transmission of an infectious pathogen in the production system.

What are the take homes for swine veterinarians to start using today? When a disease strikes, a system may need to prioritize control strategies. The results of this work help identify which farms to target first. VanderWaal explained farms with high MIP scores can be targeted and prioritized for both monitoring as well as intervention or control. Since farms with high MIPs are more likely to break and spread disease, targeting monitoring at these locations makes sense.

Likewise, when the next disease epidemic comes, MIPs can help determine which sites may need to alter management strategies such as depopulation, transport segregation, switching from multiple to single source, and vaccinating, all of which could interrupt disease spread. Furthermore, in the event of an epidemic, the approach could help to selectively manage and monitor farms grouped on the estimated risk for disease, including zoning and compartmentalization strategies, which, if planned, may contribute to significantly mitigate the impact of an epidemic on a system

While production type did not significantly impact MIP, pig movement strategies did. For example, if a nursery barn received pigs from several sow farms and then had a movement event to multiple finisher barns, that barn would likely have a high MIP and could be called a "super-spreader." Another example with a higher MIP is pulling gilts from a gilt development unit for multiple sow farms.

How is MIP calculated? It is a result of chains of farms connected via movements. Factors such as movement and pig sourcing and location all impact the number. At the end of the day, VanderWaal explains it is about incoming and outgoing contacts and the impact on risk.

For more information about analysis of movement data, identifying super-spreaders farms, and implications for disease control for farms in your system, contact Kim VanderWaal (kvw@umn.edu).

Funded by America's pork producers to protect and enhance the health of the US swine herd, the Swine Health Information Center focuses its efforts on prevention, preparedness, and response. As a conduit of information and research, SHIC encourages sharing of its publications and research for the benefit of swine health. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Paul Sundberg at psundberg@swinehealth.org.

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Paul Sundberg, Executive Director, Swine Health Information Center