*Drs. Laura Schulz and Brad Leuwerke are with the Swine Vet Center in St. Peter, Minn.
PORCINE epidemic diarrhea virus (PEDV), a virus that is new to the U.S. swine industry after first being confirmed in April, has certainly made its presence known in a short amount of time.
A cause of significant disease in pigs, infection with this virus has led to large losses among numerous sow, nursery and grow/finish sites throughout the U.S.
The way PEDV entered the U.S. swine population still remains unclear. Swine veterinarians, scientists and other industry experts continue to look for that answer since any further spread of the virus has huge implications in the fight to keep foreign animal diseases out of the U.S.
PEDV is a coronavirus, which is the same family of viruses as transmissible gastroenteritis. Both of these viruses cause severe diarrhea and high mortality (generally 100%) in pigs younger than 14 days of age. Infection with PEDV will also cause watery diarrhea and intermittent vomiting in growing and adult pigs.
The incubation period for PEDV is short. The time from exposure to the virus to the onset of clinical signs can be as short as 12-48 hours.
Clinical signs can be quite variable, with the most severe signs occurring in young pigs that cannot cope with excessive fluid and nutrient losses. In nursery-age pigs, it is sometimes difficult to differentiate between PEDV and diarrhea caused by rotavirus, Escherichia coli or salmonella, with the comment "the normal scours we see every turn" being common. Because of this, diagnostic testing is very important.
Older pigs can handle this virus fairly well, often recovering from diarrhea, vomiting and depression in a matter of days to a week. Similarly, adult pigs aren't as severely affected. Generally, at the beginning of the break, sows in lactation will be sick and start drying up, but there has been only minor death loss/abortions associated with PEDV.
Testing for this pathogen has evolved very rapidly, with many diagnostic laboratories developing their own internal polymerase chain reaction (PCR) tests to detect the actual virus in submitted samples. Veterinary diagnostic laboratories have tested fecal samples and also oral fluid samples from positive and negative sites, comparing the ability of oral fluids to work as a diagnostic sample. At this point, oral fluids look to be valid samples to collect for PEDV diagnosis. Other acceptable samples for PEDV PCR tests include rectal swabs, environmental swabs and postmortem tissue samples.
Diagnostic labs are also developing antibody tests for PEDV, which will allow veterinarians to look backwards through time at a group of animals to determine if they've historically been exposed to PEDV. It may also allow for measuring the success of whole herd/gilt developer unit exposure.
Since the detection of PEDV in the U.S., several studies have been completed investigating possible routes of transmission of the virus. One of the early studies, carried out by the American Association of Swine Veterinarians and the National Pork Board, with the help of numerous veterinarians, determined the prevalence and movement of PEDV related to the transport of market animals.
In brief, incoming and outgoing trailers at packing plants throughout the U.S. were swabbed to determine the frequency of infected trailers coming into plants and the risk of non-contaminated trailers becoming contaminated at the plant.
In the study, 17% of all trailers coming into the plant tested positive for PEDV. Of the trailers that were negative coming into the plant, 11% of those became contaminated at some point during the unloading process. From this, it was concluded that packing plants (also sow and cull pig collection points) could be a major route of PEDV dissemination.
It will be very difficult to clean up packing plants or any site where pigs from multiple locations are transported to and commingled. Even though PEDV losses in a market pig are far less severe than at a sow farm, keeping it out of finishing sites is still important as amplification of the virus at finisher and wean-to-finish sites creates additional risk to sow farms.
Swine producers should understand this risk and continue to work through ways to reduce the risk of contaminating a trailer at offload such as using booting and trailer entry procedures, along with lessening the risk of carrying PEDV back into their sites, such as by using truck washes, disinfection routine, drying facilities, etc.
At this time, PEDV has not been proved to infect pigs through aerosol transmission. Some air samples have tested positive via PCR assay for PEDV, but bioassays have not shown the virus to be viable in aerosol. At this time, the biggest risk for swine producers is the physical movement of PEDV into swine facilities.
The following list outlines some essential biosecurity steps for keeping out PEDV:
* Implement a "line of separation" at each entry/exit point. Since PEDV must be tracked into a farm in order to infect the pigs, it is incredibly important to focus attention on all entry and exit points and consolidate them as much as possible.
1. Chutes/animal entry/exit. As the previously outlined study showed, trailers can be a significant risk to a farm; therefore, it is critical to ensure that the farm has a clearly defined line of separation as well as a documented protocol for loading culls, sows, weaners, feeders, markets, etc. It would also be best to have a manager involved in the loading process to ensure that all steps are done to expectations. Consolidation of wean and cull chutes to one area of a site is also a good idea for better management of the sanitation of this area.
2. Supplies. All supplies that have an outer box or bag should be stripped of the outer box/bag prior to entry into the farm. Supplies that can be fumigated or wiped/sprayed down prior to entry into the farm should be. There should also be documentation of supply entry procedures, careful management of the process and consolidation to only one point of entry/exit to be successful.
3. Bench entry or showers. At the very least, people must change boots and coveralls and wash hands prior to entering a facility. Sites that may infect the downstream flow should require showers.
* Trailers. Trailers that have been to packing plants or other collection facilities must be properly washed and disinfected prior to arrival at a sow farm, nursery, gilt developer unit or any other site at which pigs will remain on the site for several additional weeks.
That being said, all trailers (and drivers) must be considered contaminated when they arrive at farms. Drying is a key step to disinfection. PEDV requires higher temperatures than transmissible gastroenteritis to be inactivated, but drying reduces its ability to survive in the environment.
Because drivers need to haul pigs to packing plants and other collection sites, it is difficult to ensure that their clothing and cabs are free of undesirable pathogens. Truck drivers should not walk on the farm's chute or into the barn as this poses a significant risk to the farm.
* Incoming gilts. Gilts coming into a PEDV-negative gilt developer unit or a sow farm should be tested for PEDV prior to being shipped to ensure that they haven't been exposed to and aren't shedding the virus.
* Boar studs. Although PEDV is not transmitted in semen, boar studs must remain PEDV free because semen can be contaminated by fecal material during the collection process and, therefore, transmit the virus to downstream sow farms.
* Training and audits. Audits and regular training of farm staff and other visitors should be part of a comprehensive biosecurity plan to ensure compliance.
* Contaminated sites. Nursery and growing pig sites with a confirmation of PEDV infection should be managed as an all-out system with the completion of the turn to allow for total cleaning, disinfection and drying.
* Manure removal. As manure removal season approaches, be aware that there is a risk of contaminated pumping equipment entering a premise. Has a policy been developed to audit sanitation processes between sites? Can pumping be completed in "like" health status sites before moving on to other sites? Are site employees aware of risks and able to maintain their lines of separation to reduce the risk of tracking yard contamination into the barn?
More is known now about PEDV than four months ago, but several questions still remain to be answered.
PEDV can be physically moved from contaminated facilities and equipment to negative pigs, leading to significant losses. The virus can survive cold weather and exposes poor biosecurity practices. Understanding where holes exist in current biosecurity procedures and addressing these will help reduce the risk of a PEDV infection in a swine herd.