WELLINGTON COUNTY – Strangles is a respiratory disease that has for centuries spread fear throughout equine communities across the globe.
While the disease, also known as equine distemper, is rarely fatal, it can cause concerning symptoms such as high fever, lack of appetite, coughing, thick white nasal discharge and severely swollen lymph nodes in the head and neck.
It gets its name because the lymph nodes can swell so severely that they are said to “strangle” the horse, restricting breathing.
Strangles is a highly contagious and serious infection that is considered endemic in most horse populations, according to the government of Ontario.
Records of the disease date back to 1251, and it can be found in almost every country in the world. Strangles affects all equids, including horses, mules, donkeys and zebras.
A strangles case was confirmed at a boarding facility in Wellington County on April 15, according to the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). The infected gelding developed a draining lymph node and nasal discharge. An additional three cases are suspected at the same facility.
Two strangles cases were confirmed at a private standardbred farm in the county late in February.
Other cases have been confirmed this year in Waterloo Region, Halton Region, Grey County, York Region, Kawartha Lakes, and Hamilton.
Since February 2023, strangles has been designated as an “immediately notifiable disease” under the Animal Health Act, meaning all veterinary diagnostic laboratories in Ontario must report positive strangles test results to OMAFRA.
The Advertiser reached out to many equine professionals for information on strangles and they kept pointing in the same direction: Dr. Allison Moore.
She is the lead veterinarian for animal health and welfare at OMAFRA, and professionals from as far away as Kentucky say she’s the best person to speak with to gain a deep understanding of the disease.
However, Moore did not respond to the Advertiser’s multiple interview requests.
She did, however, sit down with Standardbred Canada for a question and answer session all about strangles.
Moore told Standardbred Canada strangles is frequently diagnosed in Ontario, during all seasons, but it is rarely diagnosed within the horseracing industry.
Recognizing strangles
Identifying strangles as early as possible is key to reducing its spread. Temperatures often rise a day or two before the horse starts shedding the contagions, so isolating a horse as soon as its temperature rises can significantly slow the spread.
If a horse has a higher-than-usual temperature or any other signs of infection, it’s important to isolate the animal and call a veterinarian right away, experts advise.
Veterinarians can test for strangles by taking a sample and sending it to a laboratory.
Disease progression
Fever may last a few days and is typically followed by a thick white nasal discharge, in addition to swollen lymph nodes or abscesses in the neck.
“Lymph nodes infected with Streptococcus equi [the bacterium that causes strangles] become large, painful, and will eventually break open and drain pus,” provincial officials state on an Ontario webpage about the disease.
“Once the lymph nodes open and drain, the horse usually recovers quickly, [but] the pus draining from lymph nodes or present in nasal discharge contains large numbers of Streptococcus equi that can easily infect other horses.”
At times, swollen lymph nodes obstruct breathing completely or internal abscesses rupture and lead to septic shock.
It’s possible for abscesses to develop in the abdomen or even brain, Moore told Standardbred Canada.
And horses with strangles sometimes develop immune-mediated diseases that affect skin or muscle, she added.
“Although very rare, these consequences can be fatal,” Moore said.
Slowing the spread
Strangles is transmitted through horse-to-horse contact and can be carried on people’s skin and clothing as well as equipment.
In certain wet conditions, the disease can survive for up to six weeks without a host.
“It is imperative, therefore, when dealing with a horse diagnosed with strangles, or with horses of unknown health status … that shared water sources such as buckets and troughs not be used,” provincial officials state.
And during a strangles outbreak, all potentially contaminated equipment and surfaces should be cleaned with a foaming soap agent, rinsed and soaked in a liquid disinfectant.
“Typical disinfectants include Virkon and Prevail,” Moore told Standardbred Canada. “Bleach is broken down by organic debris (manure, puss, etc.) so is not ideal in this situation unless areas are thoroughly cleaned first.”
And infected and exposed horses should be isolated.
“Ideally .. in an empty barn or paddock away from other horses,” advise Ontario officials.
“If no empty barn is available, the horse should be isolated away from high traffic areas,” Moore noted.
And dedicated equipment, including wheelbarrows, shovels, forks, lead ropes and halters, should not leave the isolation area, and hay and grain for [the isolated] horses should be located in the isolation area too.
“Staff working with infected horses should wear protective clothing (such as coveralls), boot/shoe coverings (or use a foot bath) and gloves,” Ontario officials state, and staff and equipment must not go back and forth between healthy and diseased animals.
All exposed horses’ temperatures should be taken twice daily, Moore told Standardbred Canada, and if fever is detected the horse should be isolated. Checking twice daily is important, she added, as some horses only have fevers in the afternoon and some only in the morning.
Movement of horses on and off the farm should be stopped until the outbreak has cleared completely.
Most horses stop transmitting the disease within six weeks of symptoms clearing.
However, according to provincial officials, about 10 per cent of infected horses go on to become long-term carriers if proper intervention and treatment is not administered.
Horses should therefore be tested after recovery, to ensure they have not become asymptomatic carriers, provincial officials recommend.
And paddocks used by infected horses should be left empty for 28 days, Moore advises, “to allow sunlight and dry weather to destroy the bacteria.”
Treatment
“The majority of strangles cases require no treatment other than proper rest and a dry, warm stall and provision of soft, moist and palatable food of good quality while letting the disease run its course,” according to a consensus statement from the American College of Veterinary Internal Medicine (ACVIM).
In certain cases, penicillin is administered to treat strangles infections. But according to ACVIM, “veterinary opinion as to whether or not to use antibiotic treatment remains markedly divided.”
Provincial officials state that “antibiotic use is reserved for those horses that have difficulty breathing or for foals that may develop complications.”
Moore said treating with antibiotics after abscesses have formed “can delay maturation of the abscess and prolong the disease.
“In cases of exceptional biosecurity practices on the farm, veterinarians may treat horses that develop a fever with antibiotics prior to abscess development to stop the spread,” she noted.
Prevention
The best way to prevent horses from contracting strangles is limiting potential exposure to the disease, according to the consensus.
ACVIM recommends “quarantine and screening of all new arrivals, appropriate disinfection and cleaning of potentially contagious equipment, and education of caretakers on proper hygiene.
“New arrivals should be isolated for at least three weeks,” the consensus statement states.
Fallout from the disease goes beyond horses’ experiences – it can also have significant financial impacts.
“The disease [causes] substantial economic losses to the equine industry worldwide, directly due to treatment for prolonged duration, extended recovery period and other serious complications, and indirectly due to limitation of house movement and cancellation of equestrian events,” states an article published in Microbial Pathogenesis science journal in 2023.
Iceland is the only place where strangles is not present in horse populations – where the import of horses has been banned for over 1,000 years, states the Microbial Pathogenesis article.
