WHILE it is unlikely that porcine epidemic diarrhea virus (PEDV) will be eradicated from the U.S. hog population anytime soon, there is a growing urgency to better understand the virus and how it can be managed on farm to minimize the risk and losses.
Estimates are that some 3 million — or even, perhaps, upwards of 5 million — pigs were lost to PEDV in 2013.
With an increasing number of new cases of the virus being diagnosed each week, the scientific community is largely focused on vaccine development and intentional exposure of the virus.
Intentional exposure of sows to PEDV started shortly after the virus was first identified in the U.S. this spring.
Efforts currently underway at Iowa State University's Veterinary Diagnostic Laboratory in Ames, Iowa, are working to frame up what has been learned to date and to add some standardization to the process.
The main goal of controlled oral exposure, or feedback of PEDV, is to establish herd immunity in order to minimize the overall time period of associated baby pig deaths on a farm. In general, when the virus hits, the result is a five-week window of non-production on a farm.
Iowa State's Dr. Kent Schwartz believes intentional exposure of the virus can shorten that window by two to three weeks.
To achieve the highest level of herd immunity in the feedback process, Schwartz and his colleagues have found that it is necessary to infect all sows and gilts within a narrow window of exposure time.
Since the feces of suckling piglets tend to contain 10,000 times more virus per unit of volume than sow feces or the intestines of piglets, it has been identified as the best material for use in the controlled exposure of a sow herd.
Schwartz said it takes just a small amount of the virus to build immunity in a sow. In fact, he noted that just a thimble full of PEDV is enough to infect the entire U.S. swine herd.
In terms of intentionally delivering the virus to sows, Schwartz and his colleagues suggested that fluid from piglets can be trigger-sprayed or syringed in small amounts into the oral cavity of the sows and gilts. From there, they said, the virus replicates in the small intestine's enterocytes, passing immunity to the unborn piglets through the sows' colostrum.
The vaccination of sows for PEDV is something that is being tried on some farms. Harrisvaccines has so far distributed nearly 800,000 doses of a newly developed vaccine called iPED.
Dr. Hank Harris, founder of the company, explained that the vaccine produces neutralizing antibodies that are expressed from the sow to the piglets in her colostrum.
Harrisvaccines introduced iPED in the fall of 2013, only a few months after PEDV was first discovered in the U.S. pig population. An upgraded version of the vaccine, iPED+, is in the works, which Harrisvaccines hopes to have available at the end of January or in early February.
Harris said iPED is being used at 7-21 days prefarrowing in previously infected sows to provide an immunity boost. The vaccine appears to increase the effectiveness of a farm's intentional virus feedback effort, he said. Development of a vaccine to prevent an outbreak of PEDV in a naive sow herd is the ultimate goal.
Harris noted that the vaccine and intentional feedback are working to reduce piglet mortality. There are still some losses and some pigs with diarrhea, but reductions in piglet mortality overall are being observed.
Harrisvaccines is working with the U.S. Department of Agriculture's Center for Veterinary Biologics in Ames to receive conditional use licensing on its vaccine. The licensing is needed to sell the vaccine commercially. Presently, iPED requires a veterinary script for use.
PEDV was first detected in the U.S. in April 2013. The virus poses no known public health or food safety threat and only affects pigs.
The clinical signs of the virus include severe diarrhea and vomiting. It is transferred through animal-to-animal contact as well as fecal-to-oral transmission. It is not an airborne threat. PEDV is particularly deadly to piglets younger than seven days of age.