Insights into strangles in the UK

 A new study from the Royal Veterinary College (RVC), analysing laboratory diagnoses of strangles across the UK, paves the way for an improved understanding of the spread and control of strangles to reduce the impact of this devastating disease.

Strangles is a contagious upper respiratory tract infection, caused by the bacterium Streptococcus equi, which can affect horses, ponies and donkeys of any age, breed or sex with younger horses typically more severely affected. It is also one of the most prevalent infectious diseases amongst horses and ponies worldwide, carrying a very high welfare burden with up to 100% of horses in outbreaks becoming affected.

 

This study, funded by The Horse Trust, brought together an international team from the RVC, the University of Melbourne, jDATA, Intervacc AB, Wellcome Trust Sanger Institute and the British Horseracing Authority. A full report of the work is published in the Veterinary Record.

 

Researchers analysed data from seven UK diagnostic laboratories between January 2015 and December 2019, finding that 1,617 laboratory diagnoses of strangles were recorded during that time. However, considering the number of potentially undiagnosed horses, the true number of equids affected by strangles is thought to be much higher.

 

Importantly, the findings of this study begin to quantify the occurrence of strangles within the UK and guide veterinary surgeons in their approach to disease diagnosis. This includes not ruling out a strangles diagnosis when a horse or pony presents with more general clinical signs of nasal discharge, with or without fever, in the absence of abscessation or swelling of the submandibular and retropharyngeal lymph nodes. More generally, the study suggested that the description of ‘classical’ and ‘atypical’ clinical signs should be revised.

 

The study also provides a valuable resource for UK horse owners in the form of an online tool to identify if strangles outbreaks have occurred in their area, or a region they may be travelling to with their horses. This resource is actively updated – so if a region is currently experiencing higher numbers of strangles diagnoses, owners can stay informed and subsequently heighten their biosecurity and hygiene protocols. This will help to reduce the spread of strangles and ultimately the impact it can have on yards, owners and horses.

 

This resource is actively updated meaning that if a region is currently experiencing higher numbers of strangles diagnoses, owners can stay informed and subsequently heighten their biosecurity and hygiene protocols. This will help to reduce the spread of strangles and ultimately the impact it can have on yards, owners and horses.

 

The publication also reinforces the benefit of a united front for strangles research and how through laboratories, veterinary practices and owners working together, we can provide much more detailed insights into the disease, leading towards safeguarding the health of our horses.

Abigail McGlennon, PhD student in the Department of Pathobiology and Population Sciences, Royal Veterinary College, and lead author of the report, said: “Prior to the development of the Surveillance of Equine Strangles network in 2018, there was limited information available about strangles diagnoses in the UK. This publication highlights the prevalence of strangles in the UK and the variation in signs that infected horses show. The results of this five-year surveillance study enable the continued development of evidence-based recommendations within the equine industry to help reduce the spread of strangles and keep our horses healthy and happy.” 

 

For more details, see the full (open access) article:

 

Surveillance of strangles in UK horses between 2015 and 2019 based on laboratory detection of Streptococcus equi. 

McGlennon A, Waller A, Verheyen K, Slater J, Grewar J, Aanensen D, Newton R. 

Vet Rec. 2021;e948.  

 https://doi.org/10.1002/vetr.948

 

To visit the Surveillance of Strangles website, go to :

https://app.jshiny.com/jdata/ses/sesview/

Improved strangles tracking

Strangles is one of the most commonly diagnosed infectious diseases of horses. Infection results in significant health and welfare consequences and economic costs. Most affected horses recover, however about 10% remain as carriers, free of clinical signs but capable of spreading the disease.

In the largest ever study of its kind into an equine pathogen, scientists in 18 countries used the latest DNA sequencing techniques to track the bacteria Streptococcus equi as it caused the disease strangles in horses around the world.

 

They analysed data on 670 Streptococcus equi isolates that had been recovered from 19 different countries. 

 

“Using standard diagnostic testing, the Streptococcus equi strains look almost identical, however by carefully examining the DNA of the bacteria, we have been able to track different variants as they spread across the world” said Prof. Matthew Holden of the University of St Andrews. “Piecing the puzzle together, we showed that cases in Argentina, the United Kingdom and the United Arab Emirates were closely linked. Along with other examples, we provide evidence that the global trade and movement of horses is helping to spread the disease.”

 

“Building on top of the data generated, we provide an online surveillance platform for strangles enabling labs to upload and interpret their genomic and epidemiological data in close to real-time. Pathogenwatch will be used to monitor the emergence and spread of new lineages to help inform interventions and policy making decisions” said Prof David Aanensen of The Centre for Genomic Pathogen Surveillance, University of Oxford.

 

The work, is published in the journal Microbial Genomics.

 

The authors urge that the World Organisation for Animal Health (OIE) recognise the international importance of strangles. They suggest that identifying horses that are infected with S equi before or immediately after transportation would yield significant benefits

 

“This has been an incredible team effort, which was only possible through the collaboration of leading researchers from twenty-nine different scientific institutes in eighteen countries” said Dr. Andrew Waller of Intervacc AB. “Horses are transported all over the world as they move to new premises or attend competitions and events. New cases of strangles can be prevented by treating carriers before they pass on the bacteria. This new research in the field of strangles and the new online Pathogenwatch resource provide an opportunity to track the course of infections, reigning-in Streptococcus equi’s globetrotting lifestyle by shutting the stable door before this horse pathogen has bolted!”

 

For more details, see:

 

DNA investigation highlights the ‘unbridled globetrotting’ of the Strangles pathogen in horses 

Microbial genetics (2021)

https://doi.org/10.1099/mgen.0.000528

Research funding announced

The Grayson-Jockey Club Research Foundation has announced funding of $1,638,434 towards 12 new projects, 12 continuing projects, and two career development awards each worth $20,000. 

New studies being supported this year include:

 

“Passive immunization of foals with RNA-AB against R equi.” Led by Jeroen Pollet, the project at Baylor College of Medicine will follow on from previous work that showed that poly-N-acetyl glucosamine (PNAG) anttibodies can protect foals against Rhodococcus equi (R. equi) infection. 

 

Currently, these protective antibodies can be acquired by foals drinking çolostrum from a vaccinated mare or by a blood transfusion. But now the research team want to develop a new vaccine to give newborn foals instant protection against R equi infection. 

 

They explain that the vaccine comprises lab-made messenger RNA molecules (mRNA), which are a blueprint that can be used to instruct cells to produce protective PNAG binding antibodies. “We intend to administer the mRNA therapy by using a nebulizer, to let the foals inhale the RNA. This way, we hope to make the procedure less invasive and have mRNA delivered to lung cells where the antibodies are most needed for protection against R. equi. The proposed project would be the first study developing an mRNA therapy for horses.”

 

A University of Minnesota project led by Molly McCue aims to use resting electrocardiograms (ECGs) to identify horses with irregular heart rhythms at exercise that can cause sudden cardiac death (SCD.  They anticipate that this should allow increased monitoring and improved understanding of SCD. 

 

Thomas Koch, at the University of Guelph, has gained funding for research that will assess the use of equine umbilical cord blood-derived mesenchymal stromal cells to treat joint injuries in horses. 

 

A Texas A&M University study led by Noah Cohen will look at developing a more accurate blood test to identify horses infected with the Streptococcus equi to improve control and prevention of strangles. 

 

Further details of these and all the other projects supported by this year’s Grayson Jockey Club research grants are available at:

 

http://www.grayson-jockeyclub.org/default.asp?section=2&area=Research&menu=2

Challenge of identifying asymptomatic strangles carriers

A recent study found that blood tests (serology) alone did not effectively distinguish asymptomatic strangles carriers from non-carriers.

Symptomless carriers present the biggest risk of introducing strangles to a previously unaffected population.

Most horses throw off the infection, caused by Streptococcus equi, within a few months of an outbreak. But some remain infectious. These carriers usually retain the infection in the guttural pouches at the back of the throat. They carry and excrete the bacteria without showing any sign of disease.

The best way to identify carriers is by culturing a series of swabs from the nasopharynx, or by examining a guttural pouch wash for Streptococcus equi DNA (a qPCR test). Such methods can be time consuming and costly.

Serological testing for S. equi antibodies has become popular in clinical practice to screen for strangles carriers. However, a growing body of research suggests that this method cannot be relied on.

A study by John Pringle and colleagues at the Swedish University of Agricultural Sciences, Uppsala, and the Equine Veterinary Clinic, Destedt, Germany, followed three groups of horses for between six months and two years after strangles outbreaks.  A full report of the work is published in the Journal of Veterinary Internal Medicine.

Carriers were defined as horses from which S. equi could be cultured, or S. equi DNA could be found on qPCR test, in samples from the nasopharynx or guttural pouches.

The researchers compared the clinical appearance, guttural pouch endoscopy, and inflammatory markers between carriers and non-carriers and found no real difference between the two groups. Neither did serology distinguish carriers from non-carriers.

“Of particular concern however was that two of the culture positive carriers 14 months after outbreak A, and the culture positive mare associated with outbreak A tested seronegative,” they report, “suggesting lack of persistence of seropositivity despite carriage of viable S. equi.”

They conclude: “Silent carriers of S. equi do not differ clinically or on markers of inflammation to their noncarrier herd‐mates. Moreover, serology alone will not distinguish carriers in comingled horses.”

For more details, see the Open Access article:

Markers of long term silent carriers of Streptococcus equi ssp. equi in horses
John Pringle, Monica Venner, Lisa Tscheschlok , Andrew S. Waller, Miia Riihimäki
Journal of Veterinary Internal Medicine
https://doi.org/10.1111/jvim.15939

Screening for strangles carriers

Serological screening cannot be relied on to prove a horse is not a strangles carrier, a recent report warns.

Asymptomatic carriers are probably the main way that strangles gains access to a previously unaffected yard. Most horses throw off the infection within a few months of an outbreak. But some remain infectious. They carry and excrete the bacteria without showing signs of disease.

These carriers usually retain the infection in the guttural pouches. With time, pus may solidify to form masses known as “chondroids”. These can harbour the bacteria and excrete them intermittently in the nasal secretions - acting as a source of infection for other horses.

The best way of identifying strangles carriers is by culturing a series of swabs from the nasopharynx, or by examining a guttural pouch wash for Streptococcus equi DNA (a PCR test). This can be time consuming and costly.

Blood samples are easier to obtain, and serological testing for Strep equi antibodies has become popular in clinical practice to screen for strangles carriers.

However, recent research suggests that such results should be interpreted with caution and cannot be relied on to be certain a horse is not a strangles carrier.

In a retrospective clinical study, Andy Durham and Jeremy Kemp-Symonds, compared results obtained by serological testing for antibodies against S equi antigens A and C, with the findings of microbiological sampling of the guttural pouches.

The study included 287 horses, that were examined as part of routine surveillance and quarantine procedures on arrival at a welfare charity quarantine unit. Guttural pouch washes were submitted for culture and PCR testing and blood samples were tested for the Strangles A/C ELISA.

(The Strangles A/C ELISA test gives results in terms of optical density (OD). An OD ≥0.5 to either antigen A or C is considered “positive”; OD≤0.2 “negative”; and OD 0.3-0.4 “borderline”.)

The investigators found no significant association between serological status and the presence of S equi in the guttural pouches. 

S equi was found in the guttural pouches of nine horses (3.1%). Of those, only one (11%) was seropositive using a cut-off of OD ≥0.5. A further two horses fell in the borderline category, leaving six horses with negative results.

So, in this study, over half of the horses with S equi in the guttural pouches, were negative on the Strangles A/C ELISA test.

Durham and Kemp-Symonds conclude: “It would appear that the only currently reliable means of determining S. equi carrier status is microbiological sampling rather than serological screening.

For more details, see:

Failure of serological testing for antigens A and C of Streptococcus equi subspecies equi to identify guttural pouch carriers.

Durham AE, Kemp Symonds J.

Equine Vet J. (2020)

 doi: 10.1111/evj.13276

New online tool to track strangles outbreaks

Owners and veterinary surgeons can now get up to date information about strangles outbreaks in the United Kingdom thanks to a new online tool that has been developed by the Animal Health Trust (AHT). 

Strangles is a common infectious disease of horses that is found throughout the world. Not only is it an important welfare concern, but it also causes significant economic costs to owners and disruption of competition schedules.

The website, developed by the Animal Heath Trust, with support of the Horse Trust and SEIB, Is part of the Surveillance of Equine Strangles project, which was launched in 2019 by the AHT, in collaboration with the Royal Veterinary College and the Universities of Liverpool and Melbourne, and with financial support from The Horse Trust.

The developers hope that the website will prove valuable to people owning and working with horses, especially those travelling around the country to areas which have seen higher rates of strangles diagnoses.

Being able to see where strangles is being diagnosed will allow owners to increase their vigilance and biosecurity /hygiene measures when they know that they are in, or are planning to travel to, areas where there is a higher risk of encountering the disease.

 “Not only do we want to help contribute to research into Strangles but one of our key aims is to share our findings with the equine industry to help keep the UK’s horses and ponies, happy and healthy and to reduce the spread of strangles.”

The information for the website is gleaned anonymously from veterinary laboratories around the UK when they confirm a diagnosis of strangles infection. It includes data on the location of the vet practice submitting the sample, the type of horse or pony from which the sample was collected, and details of the type of sample and methods used for diagnosis.

The new online tool includes a useful mapping function, which highlights regions where cases have been confirmed. It also allows users to change date ranges so they can view information particularly relevant to them and their location.

Dr Richard Newton, Director of Disease Surveillance and Epidemiology at the Animal Health Trust, said: “This new website provides comprehensive insights about the disease in a very up-to-date manner in a way that has never been available before.

“However, the resource is only as useful as the data supplied from vets on the ground. I would urge colleagues to help us to keep this resource as up-to-date and comprehensive as possible by completing full details on submission forms being sent to any laboratory, so this information can contribute – anonymously – to the national picture of strangles.”

The Animal Health Trust now hopes to extend the online tool to include international data. This will enable meaningful comparisons to be made of strangles in different countries, which in turn could lead to new strategies on how to improve control of the disease in different parts of the world.

Abbi McGlennon, PhD student at the Animal Health Trust, who led the development of the resource, said: “Our aim with the Surveillance of Equine Strangles scheme is to reduce the spread of the disease. This website is one of the first key tools to emerge from the larger surveillance project. It joins the dots across the equine industry by collating information from laboratory confirmed strangles diagnoses and communicating this back in almost real time. I’m excited about the prospect of extending this internationally, and the difference that could make for horses globally.

For more details, see:

https://app.jshiny.com/jdata/ses/sesview/