Does the U.S. swine industry need a new surveillance approach?

"Active participatory regional surveillance" a practical approach to detecting trade-impacting diseases in today's U.S. pork industry.

Ann Hess, Content Director

May 22, 2024

5 Min Read
National Pork Board

Of the 183 countries in the World Organization of Animal Health, only 67 (36%) are free of foot-and-mouth disease. Classical swine fever virus, eradicated from the United States in 1978, is also circulating in much of the rest of the world—only 38 WOAH countries are free of CSFV.  And since African swine fever virus was first introduced into the country of Georgia in 2007, 60 countries have reported ASFV outbreaks. North American pork producers have been protected from most of this, but the world keeps getting smaller.

Does the U.S. swine industry need a new surveillance approach? Jeffrey Zimmerman, professor in the Department of Veterinary Diagnostic and Production Animal Medicine at Iowa State University, argues that it does. Why? Producers' successes have translated into more meat and pigs being shipped internationally today than ever before. For example, 15 times more pork and byproducts and 14 times more live pigs were transported globally in 2022 compared to 1961.

A lot more pigs are moving within U.S. borders, as well, Zimmerman says.

“Prior to 1990, we transported 3 to 4 million pigs across state lines each year,” Zimmerman says. “That figure jumped to 24 million in the year 2000 and, in 2022, to about 62 million pigs moved between states. With so many pigs moving so quickly across the U.S., we have little time to detect and stop the spread of a foreign disease, like ASFV or CSFV, before it is spread across the country.”

While the U.S. has conducted eradication programs in the past and continues surveillance for CSFV, pseudorabies and others, Zimmerman says that the creation of the U.S. Swine Health Improvement Plan provides the opportunity to put a new surveillance plan in place.

“We are a growing and dynamic industry,” Zimmerman says. “In 1961, when we started the classical swine fever eradication program, the average farm had 50 pigs. In 1990, when we started the pseudorabies eradication program, average farm inventory was 250 pigs. We're a much different industry today and we keep evolving. Our surveillance strategy needs to evolve, as well.”

Zimmerman suggests that the first step is to change the focus from the health status of individual herds to the health status of herds across supply chains, areas and  regions. "The traditional approach of one-by-one testing to prove each individual herd is negative is too expensive and too inefficient." 

Active participatory regional surveillance can be summed up as "a few samples from many herds routinely collected over time" across supply chains, areas and regions. This is the approach being taken in US SHIP where producers and caretakers working under the direction of their local veterinarian would collect samples from up to 10 “poor-doing” pigs, create two pooled samples, and submit to the USDA National Animal Health Laboratory Network laboratory of their choice for testing.

“You greatly improve the chance of detecting the target (ASFV, CSFV) if you selectively sample sick pigs,” Zimmerman says. “Also, if there is any question about the lab result, you can go back to the farm and re-sample the same pig or the pen from which that sample came and quickly get a definitive answer. In contrast, if you sample dead pigs, they will not be on the farm if there is a need for follow-up. That leaves difficult questions to be answered.”

Zimmerman says it’s important to note the sample collection is the most expensive component of a surveillance system. However, since US SHIP participants are already in on the farm, sampling costs are immensely reduced.

In the event of an introduction of ASFV or CSFV into the U.S., the US SHIP ASF/CSF Monitored Program involves producers outside of the foreign animal disease control areas collecting samples from 10 poor-doing pigs and combining those samples into two pooled samples. The frequency of sampling will depend on production site type and the level of risk in the area or region. For example, boar studs would collect more often than commercial herds or non-commercial herds. Which specimen is collected would be up to the producer, depending on if he or she feels more comfortable with oral swabs, oral fluids or blood swabs.

Will this new approach work? Using USDA software for simulating disease spread in livestock populations, Zimmerman and team looked at a database of 17,521 farms with 51 million pigs across eight states. At 0.1% prevalence (just 18 infected farms), the probability of detecting at least one infected farm was greater than 95%, if 60% of the producers participated by providing samples.   

“The sampling and testing component of the US SHIP ASF-CSF Monitored program is a simple plan for enhancing early detection and demonstrating evidence of freedom of disease (outside of foreign animal disease control areas). Further, in the event of the introduction of a trade impacting disease, it would support ongoing interstate commerce and the resumption of international trade over the course of the response and recovery period”,  Zimmerman says.

As far as cost, Zimmerman says the team doesn’t want to sugarcoat the cost of active participatory regional surveillance. The cost for serum or swab samples tested by PCR would be between $0.01 to $0.03 (1 to 3 cents) per pig in the region. "These costs were based on current standard practices. In particular, we think more efficient packaging and shipping options would substantially reduce costs," Zimmerman added.

“We want to maintain continuity of business. We can do that with this kind of approach. It's diagnostically sensitive, but cost effective, and it's highly adaptable,” Zimmerman says. “It could fit a variety of pathogens, including African swine fever and classical swine fever. And the important part is that we don't have to invent anything. All these parts are already in place.”

About the Author(s)

Ann Hess

Content Director, National Hog Farmer

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