A virus that has killed millions of neonatal pigs can cause multiple outbreaks on a farm within a year.
Dr. Tom Burkgren, executive director of the American Association of Swine Veterinarians, said veterinarians have seen porcine epidemic diarrhea virus outbreaks this year on farms that also had outbreaks in summer 2013, although figures on reinfections are not available. On some farms, the coronavirus has remained present since the initial outbreaks.
“I think it’s an indication that we don’t know everything there is to know about this virus yet and, in particular, we don’t know how sow immunity develops and how long-lasting it is,” he said.
PED killed an estimated 7 million pigs from the time the virus was first found in the U.S. in April 2013 to the end of April 2014, according to the National Pork Producers Council. It can kill nearly all neonatal pigs in a herd, although Dr. Burkgren said subsequent outbreaks have been connected with lower morbidity and mortality rates than outbreaks in naive herds. He did not have data on those differences.
PEDv is known to infect only pigs.
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Lack of immunity
Dr. Matt Ackerman, a practitioner in Greensburg, Indiana, identified a PED outbreak in a client’s 6,000-sow herd May 5, 2013, and biological samples showed the herd stopped shedding the virus in September. A second outbreak started during the last week of March 2014, even though the gilts that were farrowing this spring had been exposed to the PED virus during the first outbreak.
He had hoped that animals exposed to PED would be immune to the same strain for two or three years.
The second outbreak killed 30 to 40 percent of pre-weaning pigs, down from nearly 100 percent during the initial outbreak. But the first outbreak ended after eight weeks, while the second outbreak was still ongoing at the end of May, about 12 weeks after it had started.
Dr. Burkgren said Dr. Ackerman’s client reacted to the initial outbreak with appropriate actions, including efforts to immunize sows. The subsequent outbreak was concerning, he said.
Dr. Ackerman knows colleagues have exposed gilts to the virus to immunize them prior to entry to the farrowing house. But he has found that the exposure does not guarantee immunity.
“I want people to know—other colleagues to know—that just because a farm broke with PED last year doesn’t mean they’re going to be immune this year,” he said.
Whether the virus was reintroduced or has remained in the herd since the initial outbreak was a subject of debate among Dr. Ackerman’s colleagues, he said. Sequencing showed that the same virus strain was responsible for both outbreaks.
In June, the Department of Agriculture’s Animal and Plant Health Inspection Service began requiring reports when pigs are presumed or confirmed to be infected with the PED virus or the swine deltacoronavirus. The latter was found in U.S. pigs early this year and since has been connected with milder clinical disease than that associated with PED virus.
Veterinarians, diagnostic laboratory employees, and pig owners are among those who have to report positive laboratory tests for such “novel swine enteric coronavirus diseases.”
The number of infected herds peaked in February, when 1,230 herds were confirmed to have infections. The number of confirmed infections had declined through May, when 760 herds had positive test results, according to APHIS figures.
Agency data also indicate about 200 herds in 14 states were found to have swine deltacoronavirus infections from March through May, the only months for which APHIS provided data by press time.
APHIS documents also forecast a 10 percent decline in the number of hogs ready for slaughter this summer relative to summer 2013.
“A year ago, we didn’t expect PEDv and these other viruses would have this great an impact to industry,” a Q-and-A document states.
APHIS initially let industry lead efforts against the coronaviruses, but the unexpected impact showed a need for a larger government role, the document states.
“The industry is already seeing herds previously impacted by the virus become re-infected, and routine and standard disease reporting will help determine the magnitude of the disease in the United States and document progress in managing the disease,” it states.
APHIS is spending about $26 million on vaccine development, state disease response and control, herd monitoring and testing, biosecurity, diagnostic testing, and virus genomic sequencing, the agency announced in June.