The sudden and widespread appearance of a deadly swine virus is causing concern for producers. Porcine Epidemic Diarrhea Virus (PEDV) now has spread into five hog-producing states, but where it came from and how it arrived in the United States remains a mystery. PEDV previously was diagnosed in parts of Asia and Europe in the early 1980s and is a swine-only virus. As such, it poses no danger to humans or other animals, and the meat from infected pigs is safe for people to eat.
PEDV is similar to transmissible gastroenteritis (TGE) and causes severe watery diarrhea, vomiting and dehydration. It is most often fatal to young pigs. It also causes illness in older hogs, though their survival rate tends to be higher. Known as a "coronavirus" because of the crown-like spikes on its surface, the virus afflicted China in recent years and killed more than 1 million piglets.
Veterinarians and epidemiologists say pigs are infected through oral means. The virus is not airborne and does not occur spontaneously in nature. It is spread by pigs ingesting contaminated feces. Investigators are focusing on physical transmission, perhaps a PEDV infected pig, equipment marred with feces, or perhaps even a person wearing dirty boots or with dirty nails. As this is a new virus to the United States, even a small amount of virus transported on coveralls or footwear and worn onto a farm can infect the herd.
PED is labeled a “transboundary” disease by the USDA. The Food and Agriculture Organization of the United Nations (FAO) states Transboundary Animal Diseases (TADs) are defined as “those epidemic diseases which are highly contagious or transmissible and have the potential for very rapid spread, irrespective of national borders, causing serious socio-economic and possibly public health consequences.” Potential consequences of TADs are of such a magnitude that their occurrence may have a significant detrimental effect on national economies.
Sources at Michigan State University report the strain of PED virus found in the United States is 99 percent homologous (similar) to the Asian strain, which remains highly contagious. Mortality in piglets is high (up to 80 percent) due to dehydration. Mortality in sows, nursery and finisher pigs is lower with clinical signs of fever, vomiting and diarrhea. Sudden death may occur, likely due to twisted gut following vomiting.
Swine herds with confirmed PED in the United States were likely exposed to the virus 5-8 days prior to exhibiting clinical signs. The clinical expression can move through the affected barn unit rapidly, typically within 12-36 hours. Normally, producers will not see a difference in clinical signs between TGE and PED outbreaks. However, the PED virus survives well in high temperatures and is seen predominantly during the summer season. Confirmation of PED infections requires sampling and testing.
There is no treatment or effective vaccine available for PED so an emphasis should be made on prevention and control.
Cases have been reported in Iowa, Colorado, Indiana, Illinois and Minnesota, according to state veterinarians, agriculture department officials and the National Veterinary Services Laboratory in Ames, Iowa. While only seven farms had confirmed cases of PED as of publication, more cases are expected as labs sift through samples.
Overall numbers of confirmed cases and mortality rates are not yet available, though anecdotal evidence suggests there are devastating losses for farms that are hit.
"If you've got it, it's bad," says Mark Greenwood, vice president of agri-business capital at AgStar Financial Services. Although as of publication, none of Greenwood’s clients had been affected, he had spoken to a producer who experienced it in a 2,000-head barn of pigs. He had a 40 percent death loss.
PEDV source unknown
The sudden appearance of the PED virus raises questions about bio-security. It remains a mystery how the virus entered the United States, and regulatory and health officials are concerned about potential holes in the bio-security shield designed to protect the U.S. food and farming sectors.
While the United States imports millions of pigs each year from Canada, it imports pigs from virtually no other country. No Canadian cases of PEDV have been confirmed, but Canadian officials say they do not test for it.
In recent years, with the emergence of dangerous pathogens such as H1N1, also known as swine flu, and bovine spongiform encephalopathy (BSE) or mad cow disease, the United States and other countries have sought to secure defenses both on the farm and at the national borders to protect against barnyard epidemics.
"We know so little about the transmittal of this virus,” says Ronald Plain, professor of agricultural economics at University of Missouri in Columbia, Missouri. “We can't be sure if it's happening because of something we're supposed to do right and didn't - or by some mechanism we don't know that we're supposed to do differently."
Initial reporting about the virus may have been delayed, say sources, because its symptoms can be confused with transmissible gastroenteritis (TGE).
Also, states are not required to report cases of PEDV to the federal government, and farmers are not required to report to state veterinarians.
As part of its assessment of the situation, USDA will email epidemiological surveys to swine veterinarians who are dealing cases of PEDV. Meanwhile, the veterinarians are sending samples to diagnostic labs, where technicians are scrambling gathering the tools needed to check the samples for PEDV - supplies many labs did not have prior to the outbreak.
The U.S. Department of Agriculture's Animal and Plant Health Inspection Service is working with state agencies and pork industry officials to discover where the virus originated. It also is working with various state laboratories to build testing capacity to detect the PED virus. Presently, Iowa State Veterinary Diagnostic Laboratory has the testing equipment available and other Midwest labs are developing tests as well.
Protect your herd
To help protect your herd from possible infections, review your biosecurity plans and strategies to increase biosecurity protocols. These strategies would include washing and disinfection protocols for all trucks returning from market, change of footwear, change of outerwear such as coveralls and washing hands prior to entry to the barns where pigs are housed.
Ensure that you are changing footwear and coveralls when coming from a public pig area back to your farm. Other biosecurity measures include limiting visitors onto the farm site and washing and disinfecting transporting equipment with a 6 percent chlorine solution at a 1:32 ratio. Also ensure that other fomites such as equipment is clean and disinfected prior to entry of your barn. Limit movement of equipment such as shovels, snares and syringes to one location. Incoming stock should be held offsite for a minimum of 28 days.
In the event that PED circulates on your farm, suckling pigs should have free access to water to help decrease dehydration. Immunity can only be developed through exposure and many producers will try to eradicate the virus through blanket exposure to all pigs, especially in farrowing units, through feedback procedures. However, feedback procedures have drawbacks in that it also spreads other herd viruses. Consult with your herd health advisor prior to implementation of a feedback program.
Sanitary and quarantine measures can help slow the spread of the virus. Introduction of new stock should also be suspended during an outbreak, or coordinated such that incoming gilts are exposed at the same time as the rest of the herd.
Contact your veterinarian if you suspect PED or TGE to develop testing and immune response strategies. PED is not a reportable disease although this is the first time that is has been detected in the United States.
If you suspect PED on your farm, contact your veterinarian or the Iowa State Veterinary Diagnostic Laboratory to determine the best laboratory services for your location. Producers and veterinarians looking to submit samples to the Iowa State University Laboratory should collect samples from pigs expressing clinical signs of the disease. Fresh samples from the small intestine and colon, along with feces collections are preferred.
China Hard Hit with PED
Veterinarians and agricultural epidemiologists in the United States are drawing grim lessons from the devastating effect PEDV has had in other countries.
The first reports of suspected PEDV came in 1971 in the United Kingdom. As years passed, PEDV spread across parts of Europe and Asia. Veterinary researchers later concluded that lax bio-security measures contributed to PEDV's spread in Asia.
One of the worst known outbreaks of the virus hit Chinese pig herds in late 2010, according to the Centers for Disease Control and Prevention's Emerging Infectious Diseases Journal. Vaccines had limited effectiveness and PEDV over ran southern China, killing more than 1 million piglets. The death rate for virus-infected piglets ranged from 80 percent to 100 percent.
But the food shield is not impermeable. "If it becomes clear that this is not a novel way for PEDV to be transmitted, and that there had to be physical contact, that's going to be a major concern," says William Marler, a leading food-safety attorney. "It means that there was a failure in the system."