About Strangles

Strangles is the most commonly diagnosed infectious equine disease in the world. It is caused by the bacterium Streptococcus equi and can prove fatal. Clinical signs include fever, profuse nasal discharge and abscessed lymph nodes of the head and neck. The swelling of these lymph nodes may, in severe cases, restrict the airway, hence the name ‘Strangles’.

Scientists at the Animal Health Trust have discovered that S. equi has genetic characteristics typically found in Yersinia pestis – the causative agent of human plague, which also causes lymph node abscesses. Although S. equi does not present a risk to people, it could be said to represent the equine equivalent of human plague.

Strangles not only causes great pain and distress to horses but in some outbreaks can kill up to ten per cent of animals infected. It can also be an economic disaster for affected yards which often have to shut down for months. Getting rid of Strangles depends on pioneering new research.

Most animals recover quickly from the disease, although some are very ill for several days and about 1 per cent may die. Abscesses occasionally form in lymph nodes and body organs distant from the head and neck in a severe condition known as ‘bastard strangles’. The infection may also trigger a disease known as purpura haemorrhagica, which causes bleeding into the gums and organs such as the lungs, which is often fatal.

How is Strangles diagnosed?

Diagnosis is made by culturing pus from enlarged lymph nodes, nasal discharge or throat swabs. A PCR test is also available at the Animal Health Trust, which increases the chances of identifying infected horses. A new blood test has been developed at the Animal Health Trust, through research funded by The Horse Trust and the Breaking the Strangles Hold campaign, aimed at improving the veterinarian’s ability to identify infected horses in the future.

Is it possible to vaccinate against strangles?

The Animal Health Trust is currently conducting exciting new research to evaluate a new strangles vaccine for intramuscular administration. The Strangles vaccine is based on manipulating the DNA of the bacteria to ensure a response from the horse’s immune system that will prevent infection if the animal comes into contact with the real bacteria. This is a complex and difficult task as it involves creating a live attenuated vaccine sufficiently close to the real bacteria to be effective, but sufficiently altered so that it will not revert back to the harmful strain.

The Breaking the Strangles Hold campaign aims to raise £250,000 for the production of this vaccine and has benefited from funding from the European Breeders Fund.

How is Strangles spread?

The ease with which the disease spreads through groups of animals is largely dependent on management practices. Transmission usually requires fairly close contact between infected and susceptible animals.

Mechanical transmission is common and it is important that tack is not shared and that handlers change clothes and cleanse hands thoroughly before moving between horses. Spread occurs frequently through shared water sources where the bacterium will live for periods of over a month. Regular disinfection of water troughs and isolation of infected horses is strongly recommended.

The incubation period of strangles is 7 to 14 days. However, because infected horses can shed the bacterium for long periods, the interval between new cases in an outbreak can be up to 3 weeks or more.

CASE STUDY

Thanks to our Strangles Campaign, newborn foal “Pocco” escaped the potentially fatal disease when Mum Bobbles was affected by an outbreak in Norfolk.

Chris Dobson had read about the Strangles campaign in spring 2007, and only weeks later was suspicious that her yard had been hit by the disease. She duly contacted the AHT and the vet who visited discovered that the disease had already spread widely.

After two months of careful monitoring, all the affected cases appeared to have recovered although tests showed that Bobbles was a carrier and needed to be isolated immediately. But Bobbles was pregnant and there was a very high chance that her foal would be infected soon after birth. As the fatality rate in young animals is very high the mare was treated with penicillin and the infection cleared completely before Pocco was born.

This story has a happy ending, but the case serves as a sharp reminder of the danger of this dreadful disease.

Photos of Strangles