Just got alerted by Paula Olsiewski & Eileen Choffnes to this paper Role of Transportation in Spread of Porcine Epidemic Diarrhea Virus Infection, United States by James Lowe, Phillip Gauger, Karen Harmon, Jianqiang Zhang, Joseph Connor, Paul Yeske, Timothy Loula, Ian Levis, Luc Dufresne, and Rodger Main. The paper is in the CDC journal “Emerging Infectious Diseases” and is freely available. I am calling this post a “pre-journal club” because I thought it might be good to post some quick thoughts and see what others thought of the paper too.
The paper reports on a study of PEDV – porcine epidemic diarrhea virus which was detected in pigs in the US in 2013. And the study did some sampling of the trailers used to transport pigs and reported some interesting results and conclusions. The abstract of the paper is as follows:
“After porcine epidemic diarrhea virus (PEDV) was detected in the United States in 2013, we tested environmental samples from trailers in which pigs had been transported. PEDV was found in 5.2% of trailers not contaminated at arrival, , suggesting that the transport process is a source of transmission if adequate hygiene measures are not implemented.”
This is an interesting and potentially important finding. And I commend the authors for getting out the results quickly and in an open / free journal.
However, I am not completely convinced of their conclusions. I am not not convinced either. But I am somewhere in between.
On first look, the one thing that makes me less than convinced is that as far as I can tell the authors only took one sample per trailer / time point. To get samples they used the following approach:
“Sample collection consisted of rubbing a phosphate-buffered saline—moistened pad (Swiffer, Procter & Gamble, Cincinnati, OH, USA) over an â‰ˆ900 cm2 area of the trailer floor, 15 cm from the rear door. “
Then these samples were assayed via real-time reverse transcription PCR to test for the presence / absence / amount of PEDV.
I like the specificity of their methods section. However, there are a variety of reasons to think that another sample collected in the same way might not produce the same results. The concern I have about this is as follows:
One of their key findings is that some trailers tested negative for PEDV before pigs were unloaded and then tested positive after the pigs were unloaded. This might mean (as they concluded) that the trailers got contaminated in association with the unloading. However, given that the frequency of positive results (i.e., detection of PEDV) in samples was pretty low jt seems plausible that the presence of PEDV in some trailers could have just been missed in the original sampling. Thus it would be nice to see some information on biological and technical replications of the sampling.
Again, the paper seems interesting to me. But it also seems, well, preliminary.
Any other thoughts would be welcome.