Photo of a woman (Viktoria Langwallner, SLU) standing outdoors in late summer with a brown horse.
Photo: Lisa Chröisty, SLU

Protecting horses against strangles—from vaccine details to attitudes and infection control in practical terms

News published:  27/09/2026

Painful, persistent and pervasive; the equine disease that can “strangle” horses is found worldwide. After many years of research, a Swedish vaccine became available. Now, five years later, the research begins anew with the aim to deeper understand: how does the protection we offer our horses work?

Strangles – the name itself hints at what this equine disease can do. Caused by the bacterium Streptococcus equi, it makes the lymph nodes in the horse’s head and neck region swell and sometimes develop into abscesses. In severe cases, the swelling can obstruct the horse’s airway.

In other cases, the abscesses burst, both on the outside and inside the horse's body, and I don't think we need to say more to understand that this is a disease no one wants, says doctoral student Viktoria Langwallner.

Despite the occasionally severe symptoms, most horses survive without such a dire outcome. But that does not prevent the infection—strangles—from spreading rapidly among horses once the bacteria have taken hold. Equine facilities affected by an outbreak face a prolonged shutdown, isolation, and quarantine—often with significant consequences and losses.

When strangles are detected on a farm, the Swedish Veterinary Institute (SVA) recommends that the stable is kept isolated for four to six weeks after the last affected horse has stopped showing symptoms. This entails a long period of disease control and recovery, explains the doctoral student.

To protect horses, research was conducted for many years into the possibility of developing a vaccine. Eventually, researchers at the Swedish University of Agricultural Sciences, Karolinska Institutet, and the Animal Health Trust, in collaboration with the company Intervacc, found a formula that worked.

And just over four years ago, this vaccine became available for Swedish horses, says Viktoria Langwallner.

To vaccinate or not to vaccinate?

Although the vaccine has been available in Sweden for several years, the percentage of vaccinated horses remains relatively low. Why this is the case is one of the questions this research study aims to answer.

Questions about the vaccine will be investigated both in the lab and among horse owners and veterinarians, says Viktoria Langwallner.

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Some of the research takes place at the molecular scale. Several members of the research team, including the doctoral student, specialise in studying proteins – some of the building blocks that make up the vaccine.

We know that the vaccine is effective and generally works well, but we are now conducting further research to gain an even better understanding of how the various components of the vaccine work and how the horse's immune system responds to them, she continues.

The researchers are also investigating how antibodies and immunity develop in horses. Among other things, they are studying how antibodies are transferred from mare to foal and whether it is possible to detect antibodies in saliva in the same way as in blood samples.

But the project doesn't just stay in the lab. To understand how protection against strangles works in practice, researchers also need to study how decisions regarding vaccination and infection control are made.

After all, the spread of strangles is influenced both by the characteristics of the bacteria and by how people working with horses approach biosecurity, infection control, and vaccination. Therefore, the project is investigating which factors influence the choices that are made—both regarding vaccination and other preventive infection control measures. The goal is to contribute with knowledge that can be used to improve preventive efforts against the disease.

Vaccination can be a controversial topic today, and an important part of the project is to understand how horse owners, farm owners and veterinarians in Sweden view the issue, says the doctoral student.

The next step in protection against strangles

I keep coming back to the importance of building a stronger foundation of knowledge so that we can see the bigger picture more clearly. That allows us to make increasingly informed decisions – when developing new vaccines, improving existing ones, and when horse owners decide how best to protect their horses from infection, says Viktoria Langwallner.

The doctoral student hopes that the years spent on the research project will contribute to a better understanding of both the protection the vaccine provides and attitudes toward its use. These two perspectives, taken together, can help ensure better protection for Swedish horses.

At the same time, she is aware that this can be a controversial topic—something that can be both positive and problematic.

It’s good to be skeptical when you care deeply about something or someone. Even more important, however, is to be aware of what you base your opinions on. We need to give horse owners the opportunity to make decisions not based on prejudice, uncertainty, or fear, but on the knowledge that is available today—and that is constantly evolving.
Follow the project and its results on the SLU project page

Facts: About the project

  • The project’s official title is: Strangvac, a multicomponent vaccine approved for use in horses that protects against S. equi
  • The project is expected to run from 2025 to 2028 and is funded by the Swedish University of Agricultural Sciences and Intervacc.

  • The doctoral student in the project is Viktoria Langwallner, working together with a research group consisting of:
    • Principal supervisor Eva Tyden, Associate Professor and Researcher specializing in parasitology at SLU
    • Supervisor Joakim Bjerketorp, Researcher working on the development of several vaccines at SLU
    • Supervisor Sara Frosth, Senior Lecturer and Researcher specializing in bacteriology at SLU
    • Supervisor Angie Tegehall, Researcher in microbiology at SLU

      and:
    • Andrew Wallner, Chief Scientific Officer at Intervacc
    • Lars Frykberg, Researcher at SLU

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