Strangles outbreaks: what’s happening in the UK?

Strangles, where horses display clinical signs including pyrexia, inappetence, purulent nasal discharge and swelling and abscessation of the lymph nodes of the head and neck, is the most frequently diagnosed infectious disease of horses worldwide. As far as is known, only the indigenous horse population on Iceland remains free of strangles, a situation that has been maintained through minimal importation of horses for over 1,000 years and being geographically isolated. Each outbreak of strangles has the potential to involve all horses on a yard and in order to prevent further spread, movement restrictions often remaining in force for more than two months, are required.

Development of a new surveillance project

Surveillance of Equine Strangles (SES) is a project based at the Animal Health Trust, funded by the Horse Trust and SEIB Insurance Brokers. Through an expanding network of diagnostic laboratories SES is investigating where in the UK strangles is occurring through diagnostic confirmation of S. equi infections using qPCR and culture. The ability to recognise where strangles is being diagnosed enables equine vets and owners to increase their vigilance and biosecurity/hygiene measures when they know that they are in, or travelling to a higher risk area. Not only does SES contribute to strangles research, but one of our key aims is to share our findings with the equine industry, to help reduce the spread of strangles and keep the UK’s horse population healthy.

The latest update

Between April and June 2019 there were 89 laboratory confirmed diagnoses of strangles across the UK, from samples submitted by 48 veterinary practices. The number of laboratory diagnoses of S.equi in Q2 is lower than the previous quarter, where 118 diagnoses were reported. Given the increasing number of equine influenza diagnoses made in Q2, veterinary focus when attending horses with non-specific signs of respiratory disease may have been directed more at influenza rather than strangles, possibly explaining the lower numbers of laboratory diagnosed S. equi samples seen this quarter.

Through the information gathered by SES it’s possible to broadly visualise where in the UK these diagnoses are happening. In Q2 Leicestershire and Rutland saw the highest number of S. equi diagnoses followed by parts of West Sussex and Cheshire.

During Q2 over half of submitted samples were guttural pouch lavages. Sampling from the guttural pouches, although technically demanding, is one of the most effective ways to screen for S. equi long-term subclinical carriage, which if confirmed allows targeted treatment and subsequent confirmation that the animal no longer poses a subclinical infectious risk. It’s therefore encouraging to see vets utilising this sampling technique allowing for effective control either following outbreaks or of potential carriers identified after blood testing, for example prior to movement to new premises.

Advances in molecular techniques such as qPCR provide more rapid diagnostic tests with sensitivity and specificity above 90%, thereby enabling vets to confidently and quickly identify infected horses and prevent further cases of disease. SES continues to see promising figures as to the laboratory diagnosis techniques vets are requesting when submitting a sample. In Q2 65% of samples were diagnosed through qPCR alone followed by 27% combined qPCR and culture and just 8% diagnosed through requesting culture alone.

Further findings from Q2 are summarised in our quarterly infographic below:

Where to find out more?

SES creates quarterly updates which can be found following the link: https://www.aht.org.uk/disease-surveillance/surveillance-equine-strangles. We also create monthly map updates allowing vets and owners to be aware of where in the country diagnoses are being seen to help identify when extra biosecurity practices are needed.

With thanks to our project funders the Horse Trust and SEIB Insurance Brokers, and to our diagnostic laboratories for contributing this valuable data to the SES laboratory network: The Animal Health Trust’s Diagnostic Laboratory Services, Donnington Grove Veterinary Group Laboratory, Liphook Equine Hospital Laboratory, NationWide Laboratories, Rainbow Equine Hospital Laboratory, Rossdales Laboratories and Three Counties Equine Hospital Laboratory.