Virus survival time unknown factor in risk assessment

OMAHA, Neb. — U.S. officials admit they were not prepared for the devastation of porcine endemic diarrhea, which has killed millions of baby pigs since last May.

Several viruses are circulating, and how they got to North America is a puzzle.

“We don’t know how they got into the country, but we do know these are Chinese related viruses,” said veterinarian Dr. Paul Sundberg, vice-president of science and technology for the National Pork Board.

Other hog and poultry viruses have also originated in Southeast Asia and caused significant losses in North America.

“Let’s learn from history. If we got these others, what else might be coming?” he told the National Institute of Animal Agriculture conference held in Omaha April 1-4.

“If we know we are at risk from viruses coming into the country in some manner, let’s try to do an assessment of our risks for that and our preparation.”

Task forces comprising government, industry, producers and commodity groups need to collaborate on surveillance and responses to reportable and non-regulatory diseases. Officials know the procedures for outbreaks such as foot-and-mouth disease, but there is no framework for dealing with a virus like PED.

A pork industry strategy group has been formed and weekly conference calls are held to share information for control.

No one is sure how some devastating animal diseases enter a country, but there are known pathways for viruses to travel, said Lisa Ferguson, national director for policy and permitting services with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS).

A series of steps are used to track a disease’s travel itinerary.


The first thing to do when dealing with trading partners is to find out if a virus is present in a region. Next, determine if an infected or contaminated product is selected for export to the United States. Finally, learn if a virus can survive processing or long trips in a container.

U.S. inspectors look for certification or permits when a product arrives, which can be checked further if something seems amiss.

The standard practice is to rate risk of transmission.

Negligible risk means it is so rare that it does not merit consideration. Low risk is rare, medium means the event occurs regularly, and high risk indicates it occurs often.

There are also specific pathways that a disease can use to travel around the world.

It could be airborne or hitch a ride on animal tissues and fluid, conveyances and containers, farm equipment, food and feed and garbage.

Live animals may act as vectors, including livestock or germplasm, humans, micro-organisms, insects and rodents.

Feed ingredients could carry disease, although many products are processed or rendered, such as blood meal and plasma, other protein meals and fats. The origin of these can be hard to trace, and APHIS does not test them for disease

“In general, the rendering process is going to inactivate viruses,” Ferguson said.


Trade data shows the U.S. has not imported blood products, she added.

Rendered products for feed preparations may come from Canada, Mexico and Germany. Fats primarily come from Canada, Australia and New Zealand. Some ingredients are imported from China and India.

Forages, grain, byproducts, fats, oil and vitamins arrive primarily from Canada, Mexico and Argentina. There are some restrictions on plant products because of the possibility of transmitting foot-and-mouth disease on straw and hay.

“It is unknown with many of these other viruses what is the virus survival time on a plant meal or pellets,” Ferguson said.

Small amounts of milk and milk derivatives also come in, but they are considered of negligible risk because of the processing that is required.

Animal manure as a feed ingredient is a potential route, but the U.S. does not allow it in for the purpose of feeding. For example, processed manure is used as a feed ingredient in Chinese aquaculture.

Microbial cultures such as amino acids, minerals, vitamins, probiotics and B vitamins are manufactured through an industrial process, and it is considered to be a production failure if there is contamination.

Chemical synthesis or mined materials, vitamins, anticaking agents, colourants and minerals are of negligible risk. Viruses cannot propagate without living animal cells, so contamination is unlikely to survive industrial processing.