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November 7, 2013
Since its first appearance in the United States in May 2013, cases of porcine epidemic diarrhea (PED) virus have been on the rise. As of Oct. 26, 2013, PED virus infections have been detected in 924 case submissions from 18 different states, says Russ Daly, Extension veterinarian, South Dakota State University (SDSU).
“The PED virus has been detected in one grow-finish site in late May in South Dakota, with an additional environmental sample found positive in August. Detection of PED virus in U.S. swine herds is remarkable, since the virus has not previously been recognized in our country, despite its long history in Europe and Asia,” Daly says.
SDSU Develops PEDV Diagnostic Test
At South Dakota State University's Animal Disease Research and Diagnostic Laboratory, a diagnostic test was developed and made available to veterinarians within a couple weeks of the virus's first detection. Initially, a gel-based polymerase chain reaction (PCR) test was developed; following that a “real time” PCR test was perfected at SDSU as well.
“These tests can accurately differentiate PED virus from other similar viruses, and can detect the virus in very small numbers,” Daly says.
The preferred sample for the test is manure from affected pigs or intestines from pigs that have died. The main reason for having diagnostics performed is to differentiate disease due to PED virus from disease caused by similar viruses such as Transmissible Gastroenteritis (TGE) virus. Some herds may wish to monitor their buildings or vehicles for the presence of PED virus; environmental samples may be submitted for that purpose.
After the first outbreak of PED virus, a pointed effort quickly took place, and is ongoing, among veterinary diagnostic labs to perform further research on PED virus, including the development of additional diagnostic tests such as blood tests that would detect antibodies, therefore previous exposure, to the virus.
“SDSU researchers were among the first in the United States to grow the actual virus in the laboratory, a critical step in development of new tests and experiments that will help us understand the disease even better,” Daly says.
While PED and TGE viruses are very similar to each other, Daly explains that the diseases caused by them are very similar also.
“Diarrhea, most severe in young piglets, is the hallmark of infections with PED virus. This diarrhea often results in severe dehydration and death in preweaned pigs. Milder clinical signs are noted in older animals,” he says. “Even though PED virus is very closely related to TGE, immunity to TGE, through previous exposure or through vaccination programs, does not confer resistance to PED virus. There currently is no vaccine against PED virus.”
Some 144 Herds Tested in South Dakota
At SDSU to date, over 1,800 samples have been submitted and tested for PED virus since the emergence of the virus. From South Dakota herds, 168 samples have been tested as of Nov. 4, 2013 with no positive results. The previously mentioned South Dakota positive samples were detected at other diagnostic laboratories.
Daly says this would indicate either that producers and veterinarians are cognizant of the disease and do not see the need for diagnostic confirmation, or that there simply are not many suspect cases in our area.
“Reports from regulatory and local veterinarians would suggest that the latter case may be more likely,” he says.
He adds that basic biosecurity procedures should be effective in keeping the virus out of non-infected premises. The more familiar, but closely related, TGE virus infections typically occur more frequently during fall and winter months. If PED virus behaves similarly, swine producers and veterinarians may need to employ heightened vigilance as the seasons change.
“Attention to personnel and vehicle traffic, in addition to proper animal movement and isolation protocols, should be reinforced with all farm personnel,” he says. “However, producers and veterinarians should keep in mind that our state's swine herd would be very susceptible to infection with PED virus, having no previous exposure, making biosecurity efforts more important than ever.”
If cases of PED virus are suspected, Daly says producers should work with their veterinarians to determine the best diagnostic strategy.
“It's important to the industry that suspect cases get promptly investigated and confirmed with diagnostics in order for us to better understand how PED virus is affecting our U.S. and South Dakota swine populations,” he says.
To learn more, visit www.iGrow.org.
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