USDA: Porcine virus might have entered country in giant tote bags

Flexible intermediate bulk containers (FIBCs) are used to transport a variety of products. Bags similar to these may be how porcine epidemic diarrhea virus entered the U.S., according to a USDA report. Photo by Wikimedia Commons.Since the first diagnoses in April 2013, pork producers and herd veterinarians worked to mitigate the spread of porcine epidemic diarrhea virus (PEDv) as it devastated large swaths of swine across the United States. Despite efforts, infection and reinfection of herds thought to have immunity persisted. However, there is now hope that investigators have identified the virus' source of entry into the United States.

A recently released report from the U.S. Department of Agriculture (USDA) found that flexible intermediate bulk containers (FIBCs)-tote bags, essentially-were the most likely vehicle to harbor and transport the porcine virus. The large bags are made of materials such as woven polypropylene, according to the agency, and are used to transport bulk material such as vitamin and mineral mixes, dried distiller grains, pet food and soybean hulls. The bags are usually reused without disinfection. The USDA investigation found that the small spaces between the bags' woven fibers could harbor virus particles and protect them from sunlight and ultraviolet radiation.

Although the USDA says it has yet to uncover incontrovertible proof for its theory-no virus was detected in 60 FIBCs tested in August-the bags provide the most plausible scenario for entry into the country. Testing proved that the virus was stable in the woven fabric for 10 weeks at both 4 degrees C and –80 degrees C. At room temperature, the virus remained viable for five weeks. Investigation data to date has not supported people as an entry pathway, although the USDA says many persons associated with swine production travel regularly between the U.S. and Asia.

Investigators tested scenarios with four-part criteria

The USDA Root Cause Group investigated a number of possible entry path scenarios including imported products, non-regulated garbage, livestock and germplasm, humans and other live animals. The investigation required all tested scenarios to explain transit through four segments of travel: 

> The product or person carrying the U.S. outbreak virus had to be contaminated in the origin country,

> the virus had to remain viable and infectious in transit to the United States,

> the virus had to have means of dispersion to at least six geographically distinct locations in the U.S. in approximately two weeks, and

> the virus had to reach farms and infect pigs.

Scenarios also had to be compatible with herd investigation data, consultant observations and epidemiology data as well as explain why the epidemic did not reach Canada or the European Union. Flexible Intermediate Bulk Containers (FIBCs) when tested against this criteria was the most plausible of all tested scenarios.

Reports suggest China as the country of origin of the viruses that appeared in the United States, the USDA says. And viruses isolated in the U.S. have been shown to be similar to those identified in China between 2010 and 2013. However, it's unlikely that a specific route and mode of travel for PEDv will be uncovered. Since FIBCs are used for transporting many types of potentially contaminated product, investigators were unable to identify any ingredient or manufacturer that was common to all infected farms.

Still, the report says that mitigation of the virus, if it indeed is harbored by FIBCs, could be as simple as not reusing the bags or a disinfection procedure prior to reuse of the containers.

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