Scientists announce breakthrough in strangles vaccine research

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A foal with signs of Strangles.

Scientists have moved a step closer to developing a vaccine to protect horses from strangles.

Scientists from Britain’s Animal Health Trust, the Swedish University of Agricultural Sciences, the Karolinska Institute and Intervacc AB, have developed a new protein-based vaccine to protect horses from the distressing bacterial infection.

A horse with strangles showing lymph node swelling.
A horse with strangles showing lymph node swelling. © Redwings

Strangles is caused by a bacteria called Streptococcus equi, which causes horses to suffer from large pus-filled abscesses in their throat and neck.

There are an estimated 600 outbreaks of strangles each year in Britain alone. It causes significant suffering in infected horses and substantial economic cost to the British equine industry.

The researcher says their development of the new vaccine, reported in the journal Vaccine, will have tremendous benefits to the health of horses around the world.

“We are delighted to have shown that our Strangvac vaccine protected over 80% of horses from this dreadful disease,” said Professor Jan-Ingmar Flock, chief executive of Intervacc AB, the company that produced the vaccine.

“Strangles is a scourge of the equine world and the development of Strangvac has the potential to prevent many thousands of horses from falling ill each year.”

The effects of Strangles
The effects of Strangles.

Dr Andrew Waller, the head of bacteriology with the Animal Health trust, described Strangvac as an extremely exciting vaccine.

“The vaccine was designed using information from sequencing the DNA of Streptococcus equi and highlights the potential that the genome-era heralds for improving the health of animals and people.”

He said the trust was proud to have helped make the vaccine a reality towards finally breaking the hold the disease has on horses.

Professor Flock said the transfer of the manufacturing process and production of commercial batches were under way, in the push for the registration and launch of Strangvac.

It is anticipated the vaccine will be available for use during 2020.

Strangles is endemic throughout the world, with infected horses developing characteristic abscesses of the lymph nodes of the head and neck.

The researchers’ report in Vaccine describes the results of three studies.

They said their experimental data showed that vaccination with the recombinant S. equi proteins contained within Strangvac protected a susceptible natural host against challenge with a virulent strain of S. equi.

Position of lymph nodes and guttural pouches which are affected by strangles.
Position of lymph nodes and guttural pouches, which are affected by strangles. © Redwings

“We argue that the production of a vaccine to prevent strangles has to be cost-effective and the effectiveness of a multivalent fusion protein concept has here been demonstrated.”

They said one further advantage of the current vaccine is that it should be DIVA capable, meaning that testing should be able to tell the difference between infected from vaccinated animals.

“None of the antigens encompassed within the vaccine are included in the current ELISA [enzyme linked immunosorbent assay] tests for the detection of exposure to S. equi and, as it does not contain live or dead bacteria, it will not be detected by the S. equi qPCR tests [quantitative polymerase chain reaction].”

“We conclude that Strangvac 4 was immunogenic, conferred excellent levels of protection against strangles and is worthy of further development and clinical investigation.”

The full study team comprised Carl Robinson, Lars Frykberg, Margareta Flock, Bengt Guss, Andrew S. Waller, and Jan-Ingmar Flock.

Strangvac: A recombinant fusion protein vaccine that protects against strangles, caused by Streptococcus equi
Carl Robinson, Lars Frykberg, Margareta Flock, Bengt Guss, Andrew S. Waller, and Jan-Ingmar Flock.
Published in Vaccine, https://doi.org/10.1016/j.vaccine.2018.01.030

The study, published under a Creative Commons License, can he read here

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