Viral disease affects U.S. pigs
A virus deadly to swine and previously not present in the United States has been discovered in at least 11 states.
In April and May, the coronavirus that causes porcine epidemic diarrhea was found on 103 farms in Colorado, Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Nebraska, Ohio, Oklahoma, and South Dakota, according to the American Association of Swine Veterinarians. Officials with the Department of Agriculture’s Animal and Plant Health Inspection Service confirmed in May that the disease had been found in the U.S. but said the agency did not have a complete account of where the virus was found, since it was not receiving test samples submitted in all states.
The disease affects only pigs.
Dr. Rodney “Butch” Baker, director of Iowa State University’s Iowa Pork Industry Center and senior clinician for veterinary diagnostic and production animal medicine at ISU, said the disease is the most devastating to piglets, and an outbreak can kill nearly all newborns in a herd. Clinical signs of infection are similar to those of transmissible gastroenteritis, a disease more familiar on U.S. farms.
Dr. Joseph F. Connor, who delivered an educational lecture on the virus in May for the AASV, said that containing the virus involves managing risks in transportation, carcass removal, biosecurity for workers, and isolation and quarantine of incoming animals.
“Because it’s a viral infection, there is no direct treatment, and our efforts need to be toward elimination,” he said.
An AASV report indicates veterinarians can provide supportive care to maintain hydration among pigs infected with the new virus. The virus also is susceptible to common disinfectants, and sanitation and drying of pig trailers is effective in controlling the virus if the trailers are allowed to dry for three days.
ISU information recommends giving pigs a clean, dry, draft-free environment as well as clean water. The AASV and National Pork Board also are providing information at www.aasv.org and www.pork.org.
Presence in and beyond U.S.
Dr. Baker said eradicating the PED virus in the U.S. likely would be difficult, because it quickly spread and became entrenched in U.S. herds. Eradication also is less urgent for the pork industry, because the virus does not cause an internationally reportable disease, which could affect trade.
“I think it’s just going to be a production disease that we’re going to have to learn how to deal with and live with,” Dr. Baker said.
Smaller farms that do not regularly work with veterinarians and lack good biosecurity systems likely will struggle most with the disease, he said.
AASV information indicates PED was first identified in 1971 in Great Britain, and it became endemic in Asia in 1982. It also was reported in Canada in 1981 but has not been found since.
Information from ISU’s veterinary diagnostic laboratory indicates the virus remains endemic in Asia, which is connected with sporadic outbreaks in Europe. For example, Italy had an epidemic involving the virus in 2005 and 2006, and the virus is a major challenge in China, the ISU information states.
The virus spreads through feces and typically has a two- to four-day incubation period, AASV information states. Immunity develops in two to three weeks, at which time colostrum can protect neonatal pigs.
Dr. Baker said farms that expose all sows to the virus can see clinical signs of the disease disappear within six weeks. The same techniques that work in controlling and eliminating TGE should work for PED, he said.
On breed-to-wean farms, elimination starts with exposing the sow herd and three months of replacement gilts to the virus, Dr. Connor said. Those animals will develop immunity, and, after 60 days, farms can use naive pigs—typically gilts—as sentinels to find out whether shedding has stopped.
On wean-to-finish farms, the virus can be eliminated by emptying, cleaning, and disinfecting affected facilities and waiting until they dry before new animals enter, he said.
On affected farms, the disease is costly; the virus typically kills 90 percent or more of suckling pigs that are less than three weeks old, he said. Within two weeks after the initial outbreak, the mortality rate tends to drop below 50 percent for suckling pigs.
Dr. Connor said he hopes that, if herd owners and the swine industry can contain the virus, it will not become a long-term production cost.
Dr. Richard Hesse, a professor of diagnostic medicine and pathobiology at Kansas State University, noted that no vaccines are available to protect against the easily transmissible virus. He expects the disease will cause economic damage in the U.S.
“Our national herd is wide open to this agent,” he said. “There’s no herd immunity at all.”
Discovery of the virus
Dr. Baker said the PED virus was discovered after samples from animals sickened in TGE-like outbreaks during April were found to be negative for the TGE virus.
ISU’s index case samples arrived in the veterinary diagnostic laboratory in late April from a large sow farm with excellent biosecurity, Dr. Baker said. Gene sequencing revealed that the then-unknown coronavirus was virtually identical to a PED virus sequenced in China during 2012, he said.
The AASV reported on May 29 that those viruses were 99.4 percent homologous.
Dr. Baker said the source of the infections in the U.S. is unknown and the subject of speculation, but he noted that the spread through farms that have no business connection indicates to him the virus may have been spread through product contamination.
“It looks like it’s moved around the industry pretty quickly,” he said.
Modern biosecurity should be able to reliably exclude the disease from farms free of the virus, he said. In May, the pork industry had become more guarded, forcing Dr. Baker and colleagues at ISU and the National Animal Disease Center to suspend an influenza research project, as many pig farms involved in the study stopped accepting visitors.
Dr. Baker said the same security gap that let the virus enter the country could let other, more devastating animal diseases enter the country.
“It appears that our national biosecurity system failed us somehow,” Dr. Baker said. “Maybe it was a visitor, maybe it’s a product that came in from China; I don’t have any idea.
“But there’s a door open somewhere that allowed this to come in.”