What's behind the rash of porcine epidemic diarrhea in the United States?
Monday, February 3, 2014
Cold fall temperatures may be one cause, but studies also point to a breakdown in transportation biosecurity. The good news is that, so far, Canada, is PED-free
by ERNEST SANFORD
The rate of outbreaks of porcine epidemic diarrhea (PED) in the United States has escalated since mid-September. It is getting worse folks, not better!
It has been more than eight months since the first cases of PED were diagnosed south of the border. In May and June, 50-60 new outbreaks were being reported each week. Reports of new outbreaks peaked in the week of June 3, 2013. Then, for the next two to three months, about 30 new cases were being reported each week.
However, from mid-September through October, new outbreaks ramped up to above 60 new cases per week and kept increasing to over 100 new cases per week throughout November, followed by 184 new cases in the third week of December. At the end of December, 1,764 outbreaks of PED had been reported from 20 states. Table 1 shows states reporting more than 20 cases.
Are cold fall temperatures the reason for increased PED outbreaks? It was widely anticipated and feared that, once we got into the colder fall and especially the winter months, outbreaks of new cases would increase, perhaps dramatically. This is what happens with transmissible gastroenteritis (TGE) and we fully expected a similar phenomenon with PED.
Is that what has happened since we entered the fall months? Well, yes and no. A sudden increase in new outbreaks in Iowa, Kansas, Minnesota and other Midwest states in November and December clearly points to the colder fall and winter months accounting for acceleration of new outbreaks of PED.
That, however, is only part of the story. The other, perhaps more intriguing part of the story lies in North Carolina. North Carolina had its first reported case of PED on June 20, 2013, making it the 14th state to do so. By the end of December, North Carolina had moved up the ranks from 14th to second in reported outbreaks, trailing only Iowa for total number of cases (see Table 1). In June and July, reports ran about two to three new cases a week in North Carolina. In September and October, this number rose to three or four cases per day!
Also in September and October, about 50 per cent of all the new PED outbreaks in the United States were from North Carolina. September and October are not exactly "cold" months in North Carolina. So the "cold months" theory could be attributed to approximately 50 per cent of the new outbreaks being reported as we entered the fall months although, as we moved into November and December, the increase in cases in the U.S. Midwest confirmed fears that the colder months would bring a real surge of new PED outbreaks. In December, Iowa was reporting nearly 50 per cent of all new PED outbreaks in the United States.
Transport vehicles and spread of PED. What then? What can be done to stop or slow down the spread of PED? It's back to transport and trucking biosecurity. The spread of PED in North Carolina can be laid right at the feet of biosecurity breakdowns in trucking and transportation of pigs, to and from buying stations and slaughter plants. A survey of buying station procedures in North Carolina by veterinarian Dr. Matthew Turner one week after the first outbreak of PED in North Carolina revealed a near total lack of understanding or awareness of biosecurity standards and procedures at all four of the buying stations he surveyed. This echoes results of a study done by Dr. James Lowe, a swine veterinarian at the University of Illinois. His survey involved 700 livestock trucks and trailers delivering hogs to seven Midwest slaughter plants to determine their possible involvement in the spread of the PED virus (PEDV).
PEDV contamination reached as high as 65 per cent (432 of 669) of trailers tested. Some 11 per cent of the trailers arrived at the slaughter plants PEDV negative, but became PEDV positive by the time they left the plant. Seventeen per cent of the trailers arrived at the plants already PEDV positive.
The take-home from this study clearly showed that cross-contamination is common at slaughter plants. This cross-contamination is most likely the result of plant workers and truck drivers walking back and forth during deliveries, thereby picking up and spreading the virus.
What will happen in winter? Winter is here and we have already seen a dramatic increase in PED outbreaks. In addition, snow and ice can act as very effective fomites for transmission of the virus, over and above mere cold weather. We see this with TGE and there's no reason to believe that transmission of PEDV would not also benefit by the ability of snow and ice to act as frozen carriers of the virus. We'll see as we go through the winter.
Improvements in transport biosecurity. It's not all bad news on the transport biosecurity front. After the transport biosecurity surveys done by Drs. James Lowe and Matthew Turner, the U.S. industry has attempted to address the gaps identified in transport biosecurity.
Lines of separation have been proposed whereby a clean/dirty line is identified (similar to the bench separation between clean and dirty in a Danish entry system) at slaughter plants, buying stations and other points where trucks are making swine deliveries. The clean/dirty line of separation means that there would be no cross-over by personnel at the separation line.
Truckers arriving at a slaughter plant and workers at that slaughter plant or buying station are not allowed to cross over beyond the established (or imaginary) line of separation. This reduces the opportunity for cross-contamination and spread of fecal material with infectious disease agents, like the PEDV.
Reports so far are that implementation of these measures has been spotty across the United States. Until they are uniformly implemented, we can expect further spread of the virus.
PED vaccine. A PED vaccine has been developed by Harrisvaccines, a vaccine company in Ames, Iowa. The vaccine, named "iPED" and given to the sow, is currently available by veterinary prescription only and 7,770,000 doses have been shipped to producers in several states. Harrisvaccines is working with the federal Center for Veterinary Biologics to receive U.S. Department of Agriculture licensing so that the vaccine can become available commercially. The efficacy of the vaccine will become known later in the year after it is used by more producers.
How are we faring in Canada? Let's turn our attention to what's happening in Canada. The good news is that we still do not have PED anywhere in Canada. But there is a belief that it's not "if" but "when" we will get PED in Canada.
I do not subscribe to that belief. It is not inevitable that PED will spread from the United States into Canada. Sure, the possibility is high. But after more than nine months, we still do not have PED. Large numbers of trucks are returning daily to Canada after delivering pigs to U.S. facilities, either directly to slaughter plants or into barns as segregated early weaners (SEWs) or growers, and we must expect that a significant number of those trucks are harbouring live PEDV when they return to Canada. Our truckers have responded admirably to the challenge of observing biosecurity rules and taking great care to wash, disinfect and dry trucks after dropping off pigs in the United States before driving up to pig barns in Canada. That's more good news!
However, there is a downside to the trucks transporting pigs across the border. Many U.S. trucks come into Canada to pick up pigs for delivery back in their home country. These trucks pull up to our barns in Canada and pick up the pigs. Based on the surveys done in the United States, we can expect that at least 10 per cent of these trucks have the PEDV on them when they pull up to our barns in Canada. That's not good news!
So we do need to observe the line of separation with these trucks to avoid or diminish the chances of having the PEDV dropped off in Canada this way. Producers have been advised to ask truckers about their biosecurity procedures so they can better protect their herds.
Whatever we're doing has kept us free of the disease for over nine months. Furthermore, it must be noted that it wasn't until the first week of December that the first case of PED was reported in Nebraska. Nebraska is a significant Midwest pig production state bordering states like Iowa and Kansas, which are among the states with the highest numbers of reported PED cases (see Table 1). It might just be blind luck but, whatever the case may be, if Nebraska could remain free of PED for nearly nine months, there's no reason why we can't remain free for very much longer in Canada. BP
S. Ernest Sanford, DVM, Dip. Path., Diplomat ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: ernest.sanford@boehringer-ingelheim.com
