New light shed on how swine dysentery spreads

With new cases of swine dysentery reported recently in Yorkshire, Helen Clarke of BPEX looks at work that’s underway to find out more about this devastating disease

Swine dysentery always has a resonance with pig producers, especially following efforts to eradicate the disease in East Anglia around 2008. Now, a new technique is being used to identify different strains of dysentery that will help vets and producers vastly improve the way each case is controlled.

When several cases of the disease were confirmed in Yorkshire in 2011, alarm bells started to ring and producers were looking for help and support to control the problem. BPEX facilitated a meeting between affected producers, their neighbours, vets and the Animal Health and Veterinary Laboratories Agency (AHVLA) to discuss how they thought the disease was spreading and to share information on control strategies.

Although some suggestions about pattern of spread were tangible, there were a lot of anecdotal observations that clouded the picture. Fortunately, the AHVLA at Thirsk was starting to use a new laboratory technique, known as Multi-Locus Sequence Typing (MLST), that looks at the genetic makeup of Brachyspira hyodysenteriae (swine dysentery) samples and enables different strains of dysentery to be identified.

Initially, isolates from seven affected farms showed that three different groups of dysentery existed on the units, which were within about 10km of each other. This shed new light on the assumption that the farms had the same type of dysentery and were spreading it locally. Muck spreading and sharing electricians had previously been thought of as critical biosecurity weaknesses.

Instead, this new information suggested that other routes of spread, such as muck moving around on inadequately cleaned vehicles from other areas, people visiting farms or purchasing carrier pigs could be the higher risk points. This information really helped the group to focus on what their biosecurity priorities were and outlined areas where they could and should work together.

Reference library
In 2012, BPEX contracted AHVLA to use MLST on samples of swine dysentery to create a reference library for England. Nearly 250 samples have been submitted since 2006 and six distinct groups of strains found in this time period. This has helped AHVLA to pull together data on the clinical signs and treatments that have been used against these strain groups, which could help inform control strategies and biosecurity risk points.

However, this will remain confidential unless there is willingness from producers to share results and discuss openly what they think the source of their dysentery could have been and what medications they’ve used against it. It’s been interesting to see that, even within a strain group, different levels of resistance to medication have occurred. This suggests that medication technique and following the course of treatment is just as important as the selection of the drug.

It’s quite likely that there’ll be further research now these foundations have been laid. Matching resistance profiles to the main drugs used against dysentery for each strain may help vets select treatment and improve success rates, without having to undergo full depopulation of units. MLST has already helped producers, including one whose herd broke down with dysentery a second time following depopulation. It was initially thought that the same strain had reoccurred on the farm, perhaps meaning that the clean-down programme hadn’t worked. However, it turned out that a different strain had entered the farm, prompting a careful look at biosecurity procedures.

The information generated by MLST will be loaded into an international database that will help AHVLA and BPEX in identifying emerging threats. There are also plans to load the England data into a BPEX website so it’s easier to access for producers and vets. It’s hoped that, over time, producers will be willing to share more information about their cases and that this can be added to the website to help create a knowledge centre specific to the strains of dysentery we have.

As new cases occur in England, BPEX will provide support for these to be added to the library and ensure that the information we have remains up-to-date and useful for all.

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