Strangles in horses: first signs, testing, treatment and how long to isolate

What is strangles in horses?

Strangles, also called equine distemper, is a bacterial infection of the upper airway caused by Streptococcus equi subsp. equi, with abscesses in the lymph nodes of the head and throat. Merck's owner manual defines it as "an infectious, contagious disease of horses caused by Streptococcus equi equi bacteria", characterized by abscesses in the lymph tissue of the upper respiratory tract, and gives "distemper" as its other name. The name comes from what the swollen glands can do: the airway can become restricted by swollen lymph nodes, as the BHS puts it. It's an old disease, first described by Jordanus Ruffus in 1251, and still one of the most common infectious diseases of horses worldwide, according to Merck's professional chapter. Only horses, donkeys and mules get sick from it; Merck calls the bacterium "highly host-adapted".

Is strangles a virus?

No, strangles is caused by a bacterium, Streptococcus equi, not a virus. Redwings Horse Sanctuary says it plainly: "Strangles is caused by a bacteria called Streptococcus equi, not a virus." That matters for treatment, because antibiotics act on bacteria, and it's why the antibiotic question further down is a real debate rather than a non-starter.

Which horses get strangles worst?

Horses between 1 and 5 years old usually get the most severe strangles, but it occurs at any age, from foals of 3 months to older adults. Merck's professional chapter says disease is most severe in horses 1 to 5 years of age and that morbidity may reach 100% in naive horses, meaning a group that has never met the bacterium. Older horses with some leftover immunity can get a mild form that the ACVIM consensus statement calls "catarrhal or atypical strangles", and the same statement warns that these horses still shed bacteria that cause severe disease in more susceptible, often young, horses, so an older horse with nothing more than a runny nose belongs in the isolation plan too.

How do horses get strangles?

Horses catch strangles by direct contact with an infected horse, nose to nose, or indirectly through shared water, feed, buckets, tack and the clothes and hands of the people who handle them. The ACVIM consensus statement lists head-to-head and nose-to-nose contact as direct transmission, and shared housing, water, feed, twitches, tack and "the clothing and equipment of handlers and veterinarians" as indirect routes. The BHS adds the British version of that list: "stables, gates, feed buckets, piles of hay (forage), tack, lorries, trailers and even human clothing, shoes or hands". Merck notes that flies can transmit infection mechanically, and Tufts University says a barn cat or dog can pick up the bacteria and spread it to other horses, though that's thought to be very uncommon.

The awkward part is that the source often looks healthy. The consensus statement says transmission from outwardly healthy animals may be of greater importance than from sick horses in starting new outbreaks: horses that are incubating the disease, recovering, or carrying it. A UK genome study of isolates from 2015 to 2022, summarized in Vet Times in 2026, adds nuance: most infections came from horses with overt clinical signs, or from recently convalesced subclinical short-term carrier horses, and long-term carriers had less influence than previously thought. Both point the same way: a new arrival that seems fine, or a horse back from a show, is where your attention belongs. NC State's Dr. Kate Hepworth puts the flip side well: a horse alone in a pasture with no contact with other horses that suddenly runs a fever is very unlikely to have strangles.

Is strangles airborne?

Strangles is not considered an airborne disease, but a horse can cough or snort infected material several feet, and one US vet school describes it as able to be aerosolized. The BHS says the bacteria can't spread through the air, and Redwings writes that strangles is "NOT an airborne disease, though a horse can cough or snort infected material several feet." NC State's 2024 Q&A says "It can be aerosolized" and advises isolating a suspect horse at least 15 or 20 feet away, ideally in a separate barn. The difference is mostly in the wording: all three want distance between a coughing horse and the rest. The consensus statement also warns that high-pressure hoses create risk of aerosolization of bacteria when you clean.

How long does strangles live on surfaces, in water and on clothes?

Streptococcus equi survives 4 to 6 weeks in water but only 1 to 3 days on fencing and soil, and under 24 hours on sunlit wood, rubber and metal, according to the ACVIM consensus statement. The consensus statement also says it does not stay viable in feces or soil. Merck's professional chapter notes that wet, cold conditions and protection within mucoid secretions improve survival, though most organisms don't survive more than 3 days in the environment. Redwings gives two figures without naming a study: over three weeks in water at the bottom of a bucket and more than two weeks in the tread of a boot sole, which is a fair answer to how long strangles lives on clothes and boots. Merck's owner manual, reviewed in 2019, is the most cautious: it says paddocks and barn facilities should be regarded as contaminated for about 2 months after an outbreak ends.

What are the first signs of strangles in horses?

The first sign of strangles is usually a fever with dullness, often before any nasal discharge, which is why the British Horse Society tells owners to remember "hot before snot". Merck's professional chapter gives the fever as 103 to 106 °F (39.4 to 41.1 °C), and the consensus statement says it may exceed 42 °C (107.6 °F) in some cases and can last until the abscesses burst. The BHS treats a temperature above 38.5 °C, or a significant change to your horse's normal temperature, as the usual first sign, while the University of Florida uses above 101.5 °F. Knowing your own horse's normal temperature makes that "significant change" something you can actually spot.

Within 24 to 48 hours of the fever spike, Merck's owner manual says, come the classic signs: nasal discharge with mucus and pus, depression, and swollen lymph nodes under the jaw. The BHS list of strangles symptoms in horses is:

• a raised temperature;
• thick, discolored nasal discharge;
• swelling around the jaw, which can burst and release thick pus;
• lethargy, a dull and depressed horse;
• low appetite or not drinking, and difficulty swallowing;
• a lowered head and neck;
• a cough.

Sore throats change how a horse eats. The consensus statement describes horses reluctant to eat or drink, holding the head in odd positions, and a soft cough often linked to eating. When the nodes at the back of the throat swell, Merck's owner manual adds difficulty swallowing, noisy inhalation and an extended head and neck.

How long does strangles take to show?

Most horses show the first fever 3 to 14 days after exposure, but the sources give different ranges, from 3 to 8 days (EDCC) to 3 to 21 days and occasionally 28 (BHS). Merck, the ACVIM consensus statement and BEVA, the British Equine Veterinary Association, all give 3 to 14 days. The US Equine Disease Communication Center (EDCC) gives a shorter 3 to 8 days, the Horserace Betting Levy Board (HBLB) code of practice says the incubation period is usually about one week but may be longer, and the BHS says it normally takes 3 to 21 days, with times when it has taken up to 28.

In practice, the long tail is what sets quarantine. A horse that shows nothing on day four has not proved anything yet, which is why the US consensus statement isolates new arrivals for at least 3 weeks and the BHS asks owners to warn everyone their horse met in the last three weeks.

What does strangles look like? Abscesses and discharge

A strangles abscess starts as a warm, diffuse swelling under the jaw or behind the throat and usually bursts between 7 days and 4 weeks after infection, either through the skin or inward into the guttural pouch. The consensus statement describes that first warm, diffuse swelling and the timing. The consensus statement says an abscess may erupt outward through the skin, so thick pus drains under the jaw, or rupture into the airway or the guttural pouch, which shows as thick nasal discharge. About 50% of horses with pus in the guttural pouch (guttural pouch empyema) have an intermittent discharge from one nostril and a cough, so a one-sided snotty nose that keeps coming back after the horse seems better is worth mentioning to your vet. In severe cases the swollen glands squeeze the airway enough that a vet places a temporary tracheostomy, a breathing tube in the windpipe.

What does mild strangles look like?

Mild strangles can be just a slight fever, a different kind of nasal discharge and a slightly lower appetite, and some infected horses show no signs at all. The BHS calls this sub-clinical strangles and lists a mild fever, other forms of nasal discharge and a slight loss of appetite. This is the form older horses with partial immunity tend to get, and the one the consensus statement warns can still pass on virulent S. equi.

What should you do if you think your horse has strangles?

Isolate the horse at once, tell the yard owner or barn manager, stop horses moving on and off the premises, call your vet and start taking every horse's temperature twice a day. Those are the first steps on the BHS list, in this order:

1. Isolate the affected horse or horses immediately.
2. Notify your yard owner.
3. Stop all horses moving on or off the yard.
4. Call your vet.
5. Set up a traffic light system.
6. Take each horse's temperature twice daily.
7. Notify people and places your horse may have been in contact with in the last three weeks.

For the isolation itself, NC State advises a stall at least 15 or 20 feet away, ideally in a separate barn, with separate pitchforks and water buckets. Our guide to contacting your vet covers what to have ready when you call.

The traffic light system comes from the ACVIM consensus statement: three color-coded groups, separated by two layers of electric fence if they share a field so there's no nose-to-nose contact. Red holds horses with signs, amber holds horses that had direct or indirect contact, and green holds horses with no contact. The rules that make it work are equally specific:

• Temperatures twice a day. The rectal temperature of every horse in green and amber is measured twice daily, and any horse with a fever moves to red.
• Own buckets and kit per group. Color-code buckets and equipment, share no water, and disinfect water and feed buckets daily.
• Green, then amber, then red. Ideally each group has its own staff; if not, people always move from green to amber to red and not back again.
• Change everything afterward. Tufts' Dr. Alisha Gruntman recommends changing all clothes, including shoes, after handling the infected horse.
• Keep the muck heap separate. Manure and waste feed from infectious horses are composted in an isolated location, and the University of Florida adds that it is not spread on the pastures.

Twice a day, every horse, for weeks, is a lot of readings. A thermometer reading only helps if someone can see the trend, and in a shared barn the trend is usually spread over three notebooks and a whiteboard.

On a do-it-yourself livery yard with several vet practices, the BHS notes that vets will often work together to agree one plan for the whole yard and designate a lead vet. That is worth asking for on day one, so owners aren't following three slightly different sets of rules.

The door of the isolation stall is where most mistakes happen: a helper who doesn't know the rules, a farrier who comes on the wrong day, a neighbor who brings a carrot. A card on that door with the arrangements your vet agreed and the numbers to call saves a lot of explaining.

How do vets test for strangles?

Vets test for strangles by sampling the bacteria with a nasopharyngeal swab, a nasopharyngeal wash, a guttural pouch wash or pus from an abscess, usually tested by PCR, and by measuring antibodies in a blood test (ELISA). Which test fits depends on the question: is this sick horse infected, is this recovered horse still carrying it, or has this new arrival been exposed? The consensus statement calls a needle aspirate from an abscessed lymph node the optimal sample for confirming infection in a sick horse.

PCR, the polymerase chain reaction test, is about three times more sensitive than culture, but it does not distinguish between dead and live organisms. Culture proves the bacteria are alive, which is why the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) notes that a positive culture confirms the presence of live bacteria. And one negative nasal test is not the end of the story: the consensus statement says it does not signify absence of S. equi infection, particularly if the horse's signs say otherwise.

Nasal swab, nasopharyngeal wash or guttural pouch wash?

For a horse that is sick right now, vets usually sample the nose and throat; for a horse that has recovered, the guttural pouch wash is the most sensitive way to find a carrier. Merck's professional chapter ranks swabs as the least sensitive, a nasopharyngeal wash as more sensitive, and a guttural pouch wash as "the greatest sensitivity", preferred for detecting carriers. The Liphook Equine Hospital laboratory adds that acutely infected horses are unlikely to have a guttural pouch infection yet, so guttural pouch lavage is not an appropriate test for them. Swabs can still find carriers if you take enough: the HBLB code says a series of three nasopharyngeal swabs, usually a week apart, picks up more than 90% of carrier horses on at least one swab, using the long swabs with enlarged heads that reach the back of the pharynx near the guttural pouch opening.

What does a strangles blood test tell you?

A strangles blood test (ELISA) shows antibodies from exposure, roughly from 10 days to a few months ago; it does not show whether a horse is infectious now, and a negative result does not rule out a carrier. The Royal (Dick) School of Veterinary Studies in Edinburgh says horses exposed from 10 days to a few months ago probably will test positive, and horses exposed longer ago probably won't, whether or not they became carriers. Redwings notes antibodies can stay high up to eight months after strangles. The HBLB code says antibodies do not necessarily indicate that an animal is still infectious, and that negative blood results, single or paired, do not guarantee the absence of a carrier state.

Two blood tests exist. As of 2018 the consensus statement describes the A/C iELISA, available in Europe, Australia and Dubai, and the SeM titer, available in the United States and Europe. Results can come back borderline or inconclusive when antibody levels are rising or falling. We found no authoritative source that publishes the cut-off values labs use, so we don't give one here.

Strangles test before moving yards

A blood test before or on arrival at a new yard is only useful if it's recent: Redwings says an older negative test is not valid when a horse moves, and sampling should be at least 10 days after the horse goes into quarantine. Redwings explains that an older blood test is not valid when a horse moves onto a new yard and that sampling 10 days or more into quarantine gives the immune system time to react. The ACVIM consensus statement describes the same screening as a pair: a blood sample from new arrivals, and if it is negative, a second one 2 weeks later; a horse negative on both that stays free of signs is considered safe to join the herd, and one that tests positive is investigated further.

How long do strangles test results take?

A PCR result for strangles usually takes a day or two from sampling, and a culture takes longer, from one or two days up to a week. In the lab, the consensus statement says a qPCR can be completed within 1 to 2 hours, so results may be ready the day samples arrive, while culture takes a minimum of 1 to 2 days. TVMDL in Texas says PCR gives results in a day or two, and the Maine Department of Agriculture gives culture 3 to 7 days and PCR "as little as 48 hours", depending on how far the sample travels.

How much does a strangles test cost?

In the UK, the Dick Vet equine practice in Edinburgh quoted about £70 to £80 for a blood test and about £300 to £320 for a guttural pouch wash in August 2025, both excluding visit fees. Those figures come from one university practice and will differ elsewhere. We found no authoritative US source with a price, so we won't guess one; ask your practice for a quote per horse, including the farm call and the lab fee.

How is strangles treated?

Most horses with strangles need no treatment beyond rest, a dry, warm stall and soft, moist, tasty food while the disease runs its course, with your vet deciding on anything more. That is the ACVIM consensus statement almost word for word. Merck's owner manual mentions that the vet may recommend warm compresses, and the professional chapter says burst abscesses should be flushed with dilute (3% to 5%) povidone-iodine solution for several days until discharge stops, as your vet shows you. Redwings notes that soaked feed and forage make eating easier for a horse with a sore throat. In hot weather, the consensus statement recommends fan-assisted ventilation in the stall for horses with a fever.

Your vet may also give an NSAID such as phenylbutazone or flunixin meglumine, which the consensus statement says may improve the horse's demeanor and appetite, with care in dehydrated horses that aren't eating. We give no dose here; our guide to bute and Banamine explains the labels and the risks.

Do horses with strangles need antibiotics?

Most horses with uncomplicated strangles don't, and vets are genuinely divided on it; antibiotics are used for horses with breathing difficulty, trouble swallowing, long high fevers or complications, and never as a preventive. The consensus statement says veterinary opinion is "markedly divided", and the HBLB code calls antibiotic treatment controversial, with any essential treatment determined by the attending veterinary surgeon. The arguments on each side:

• Why vets hold back. Merck's owner manual says antibiotics may delay maturation and drainage of the abscesses and reduce the horse's natural buildup of immunity. Once swollen glands are visible from outside, the consensus statement says antibiotic therapy is generally ineffective.
• When vets use them. Merck lists labored breathing, difficulty swallowing, prolonged high fever, and severe lethargy or loss of appetite, and the consensus statement lists its own situations, "always at the discretion of the attending veterinarian".
• The very early window. Given within 24 hours of the onset of fever, antibiotics may arrest abscess formation and shedding, Merck's professional chapter says, with the disadvantage that the horse may not build protective immunity.
• Never as prevention. The consensus statement is blunt: antibiotics "should NOT be used as a preventative" in horses that may have been exposed.

A 2020 study by Pringle and colleagues in 41 Icelandic horses looked at what early penicillin does to immunity. Seven horses received penicillin within 11 days of the onset of fever, and "significantly fewer horses treated early (Group 1) remained seropositive by 4 to 6 months"; the authors conclude that penicillin given during acute strangles "can interfere with persistence of humoral immunity". In its summary of the same study, Redwings adds that the treated horses had similarly severe symptoms to the untreated ones. A worry you'll hear on yards is that antibiotics cause bastard strangles; the consensus statement says that theory has been proposed but data supporting this theory are lacking.

Penicillin for strangles: the label and the vet dose

Penicillin is the antibiotic of choice for strangles when a vet decides one is needed, and the dose in veterinary references is not the same as the one on the US penicillin label, so your vet sets the drug, the dose and the length of treatment. Merck's 2023 professional chapter: "If antimicrobial treatment is indicated, procaine penicillin (22,000 IU/kg, IM, q 12 h) is the antimicrobial of choice." The ACVIM consensus statement gives a range of 22,000 to 44,000 IU per kg, into the muscle every 12 hours or into the vein every 6 hours, and calls penicillin generally the drug of choice.

The FDA-approved US label for Norocillin (penicillin G procaine) lists "strangles caused by Streptococcus equi in horses" and reads: "The daily dose of penicillin is 3,000 units per pound of body weight (1 mL per 100 lbs body weight)." It adds "Treatment should not exceed four consecutive days.", "Caution: Federal law restricts this drug to use by or on the order of a licensed veterinarian." and "Do not use in horses intended for human consumption."

The two differ in units, in how often and in how long: Merck gives international units per kilogram every 12 hours, the label gives units per pound per day with a four-day limit. We don't convert or reconcile them, and you shouldn't either; the drug is prescription-only and your vet decides. We didn't check a UK penicillin label for this guide. Two more points from the consensus statement: S. equi has been consistently susceptible to penicillin, but it is consistently resistant to gentamicin, and trimethoprim-sulfa (TMS) results are variable, with the lead author reporting that it "has been seen to fail repeatedly". When your vet does prescribe, our guide to medication records covers keeping track of who gave each dose.

Does strangles go away on its own?

In most horses strangles runs its course and the horse recovers in three to four weeks with rest and good nursing, but that doesn't mean the horse is clear of the bacteria. The BHS gives three to four weeks for most horses, and Redwings says horses start to feel better after 2 to 3 weeks. Redwings also puts it this way: strangles "cannot be 'cured' once a horse is infected", but horses need veterinary input early. The catch is the guttural pouch: about 10% of horses stay infected there, which is why recovery and clearance are two different things.

How long is a horse with strangles contagious?

A horse with strangles usually starts shedding a day or two after the fever begins, most stop within 2 to 3 weeks, and without testing a recovered horse is treated as infectious for at least 6 weeks after its discharge dries up. The consensus statement says shedding does not usually begin until a day or 2 after the onset of pyrexia, fever in vet language, and persists for 2 to 3 weeks in most horses. Merck's professional chapter says within 2 to 3 days of fever, and Maine's Department of Agriculture says up to 72 hours. That short gap is what makes it possible to isolate new cases before they can transmit infection, as the consensus statement puts it, and it is the reason for twice-daily temperatures.

On the other end, the consensus statement says recovered horses may be potentially infectious for at least 6 weeks after their discharges have dried up, the BHS says around six weeks after signs of infection have gone, sometimes longer, and Maine says that without testing horses are considered infective for 6 weeks after the last clinical signs. Merck's professional chapter gives about 4 to 6 weeks after recovery, and the Liphook laboratory says cases should generally be free from infection 6 to 10 weeks after first exposure.

When can a horse come out of isolation?

A horse comes out of isolation after clearance testing: the US consensus statement starts testing no sooner than 3 weeks after signs resolve, the UK HBLB code at least 4 weeks after the last signs, and release follows a negative guttural pouch wash or three negative nasopharyngeal samples a week apart. The consensus statement says carrier testing should begin no sooner than 3 weeks after resolution of clinical signs, or 3 weeks after the last antibiotic dose. The HBLB code calls at least four weeks after the last clinical signs "the best compromise". Merck names a single guttural pouch wash tested by PCR, ideally with endoscopy, as the most sensitive means, with three negative nasopharyngeal washes 7 days apart as the alternative; the HBLB code allows three negative nasopharyngeal swabs or negative guttural pouch samples.

The consensus statement's release rule is two-part: no obvious disease in the guttural pouch on endoscopy and a negative guttural pouch lavage qPCR. For the barn as a whole, quarantine lasts at least 3 weeks after the last case resolves and all cases are declared negative. The BHS sums up why: end of outbreak testing is "the only way to make sure your horse is no longer infected". If your horse's nasal discharge lasts longer than 2 weeks, the consensus statement says a guttural pouch examination is indicated anyway.

So by the end of an outbreak there's a swab date, a result, another swab date a week later, maybe an endoscopy, and a vet's verdict, for every horse. When those live in different owners' phones, the yard ends up waiting for the one result nobody can find.

What is a strangles carrier?

A strangles carrier is a recovered horse that keeps S. equi in its guttural pouches, often in dried balls of pus called chondroids, and can shed it on and off for months or years; on average about 10% of horses in an outbreak become carriers. The consensus statement, the BHS and BEVA all give about 10%. Merck's professional chapter gives a much higher figure, up to 40% of naturally infected horses as asymptomatic carriers; the consensus statement uses 40% in a different sense, for one study in which 25 of 62 cases were still positive at least 40 days after diagnosis, with a median of 60 days. Merck also notes prolonged shedding of up to 18 months in a small number of horses, and the BHS says carriers shed particularly during times of stress.

Chondroids are smooth, oval concretions that harbor viable S. equi on their surface and within their core. Carriers can usually be treated: the vet washes the guttural pouches, removes chondroids, and uses penicillin locally and by injection, with the consensus statement noting that both topical and prolonged systemic treatment appear to improve treatment success rate. The BHS adds that carriers will need a second test two weeks later.

Can a horse get strangles twice?

Yes, though most horses are protected for a while: about 75% develop long-term immunity after strangles, while 20% to 25% can get it again within several months, according to the ACVIM consensus statement. The consensus statement gives the 75% for horses not treated with antibiotics. How long that immunity lasts varies by source: Tufts says at least a year, the University of Florida 1 to 2 years, NC State five years for about 75% of horses, and Maine up to five years.

Can strangles kill a horse?

Strangles can kill, but most horses survive: the ACVIM consensus statement reports case fatality rates of 8.1% to 9.7% in large farm outbreaks and 0.9% in a study of smaller farms with fewer than 50 horses. The consensus statement gives both figures, from 108 cases for the smaller farms. Redwings says strangles is fatal in up to 10% of cases; read with the consensus figures, that 10% is the top end in big outbreaks rather than the typical risk on a small yard. Complications develop in up to 20% of cases, a rate the consensus statement says increases with duration and intensity of exposure, and the two that do most of the damage are bastard strangles and purpura hemorrhagica.

Bastard strangles

Bastard strangles is the spread of strangles abscesses to other parts of the body; common sites are the lungs, the abdomen, the liver, spleen, kidneys and brain, according to the ACVIM consensus statement. The consensus statement uses the term for metastatic abscessation and calls it generally uncommon, although in one study on two farms 7 of 25 horses (28%) developed it. Maine's handout says such horses may develop colic signs, fever, and/or weight loss, and Merck notes that S. equi is the most common cause of brain abscess in horses, albeit rare. A horse that seemed to recover and then goes off its feed, loses weight or shows colic is a reason to call your vet back.

Purpura hemorrhagica

Purpura hemorrhagica (purpura haemorrhagica in British spelling) is an immune reaction that damages blood vessels after strangles exposure or, less often, vaccination, causing swelling of the head and legs and small hemorrhages on the gums and other mucous membranes. The consensus statement describes edema and petechial or ecchymotic hemorrhage, most often swelling of the head and then the legs or trunk. Of 53 horses with purpura in one study, 17 had been exposed to or infected with S. equi and 5 had been vaccinated with an S. equi M protein vaccine, and 3 of 22 horses with purpura after S. equi exposure did not survive. Your vet treats it, with corticosteroids as the primary treatment, and it is the reason for the vaccine rules further down.

Is there a strangles vaccine for horses?

Yes: in the US there are intramuscular extract vaccines and a live intranasal vaccine, and in the UK there is Strangvac, but there is no consensus on vaccine use, and no vaccine replaces isolation and hygiene. Redwings says vaccination should not be seen as a replacement for other biosecurity measures. The ACVIM consensus statement says there is no current consensus on the use of vaccines to prevent S. equi. The American Association of Equine Practitioners (AAEP) recommends vaccination on premises where strangles is a persistent endemic problem or for horses expected to be at high risk of exposure, and the BHS describes vaccination as an additional layer of protection. Whether the strangles vaccine is a yes or no for your horse is a risk conversation with your vet; our guide to vaccination records covers keeping track once you've decided.

Strangles vaccines in the US

The 2018 ACVIM consensus statement describes two US options: an intramuscular extract vaccine given as 3 doses 3 weeks apart, and a live intranasal vaccine given as 2 doses 2 to 3 weeks apart, both boostered yearly. For the intramuscular extract vaccine (Strepvax II in the 2018 statement), the consensus statement reports a reduction in the clinical attack rate of only 50%, a figure Merck's 2023 chapter repeats as reduced by 50%. We didn't check which products are on sale in 2026; your vet will know. The live intranasal vaccine (Pinnacle IN) goes only to healthy horses without fever or nasal discharge, is not recommended in foals under a year, and ideally comes without other vaccinations or procedures such as dental work or castration at the same visit. Merck explains why: live bacteria on the vaccinator's hands can cause abscesses at later injection sites. After the intranasal vaccine, a horse may test positive on PCR for up to 6 weeks, which matters if a test is due.

Strangvac in the UK

Strangvac, a recombinant protein vaccine from Intervacc, has been available in the UK since the summer of 2022; the primary course is two injections into the muscle four weeks apart, and experts advise boosters every 6 to 12 months depending on risk. Vet Times reported in 2026 that the vaccine, which has DIVA capability, was launched in the UK in the summer of 2022. Redwings described the primary course in 2020 as two injections given four weeks apart. On boosters the sources part ways: according to the same Vet Times article, the product information originally indicated a repeat primary course only two months after the first, while expert advice since 2024 is boosters every 6 to 12 months by level of risk, and up to every three months at exceptionally high risk. Your vet sets the interval.

DIVA means vets can tell vaccinated from infected horses, and the BHS says the UK vaccine won't cause a false positive result if your horse has to be tested. In the field reports Vet Times collected, one report found one fever and one injection-site swelling in 34 doses (5.8%), and a 2025 report found short-lived fever and localized swelling on four occasions each (11.1%). BEVA has not yet taken a position: it says it will keep appraising research and practice before adopting a position on these vaccines.

Which horses should not be vaccinated against strangles?

Horses that had strangles within the previous year, that show signs of strangles, or that have a high SeM antibody titer should not be vaccinated, because of the risk of purpura hemorrhagica. The consensus statement says horses with strangles within the previous year or with signs of strangles should not be vaccinated, and advises against vaccinating when the SeM titer is 1:3,200 or higher. Maine is stricter: it does not recommend vaccination during or within two years of a strangles outbreak. With yearly or six-monthly boosters, an outbreak date and a titer result to weigh against them, the vaccine decision depends on dates you need to be able to find.

Can humans or dogs get strangles?

People very rarely get infected with Streptococcus equi, and dogs don't get strangles, but both can carry the bacteria to other horses on clothes, hands or fur. The consensus statement says S. equi infections in debilitated humans have been reported, but are rare, and advises avoiding contact of the mouth and airways with pus. Merck says the bacterium causes clinical disease only in horses, donkeys, and mules. Tufts notes that a barn cat or dog wandering around can pick up the bacteria and spread it to other horses, though that's thought to be very uncommon. The more common carrier on two legs is you: the consensus statement names the clothing and equipment of handlers and vets as a route, and Redwings found the bacteria survive more than two weeks in the tread of a boot sole.

"Puppy strangles" in dogs is a different disease. VCA Animal Hospitals describes it as juvenile cellulitis, an uncommon skin condition of young dogs, also called sterile granulomatous dermatitis and lymphadenitis, with an immune-mediated component and a cause that has not yet been identified. Strangles in horses is a different disease: Merck says S. equi causes clinical disease only in horses, donkeys, and mules.

Is strangles reportable?

In the US, strangles has been a reportable disease since 2017, but reporting rules differ by state; in the UK, strangles is not a notifiable disease, although racehorse trainers must report it to the British Horseracing Authority. Merck's professional chapter says strangles became reportable in the US in 2017, although individual state guidelines vary. Maine, for example, lists it as a reportable disease in the State of Maine, and the University of Florida notes that in Florida the state veterinarian will assist with isolation and quarantine. Your vet knows your state's rules.

For US strangles outbreaks in 2025 and 2026, the EDCC publishes confirmed cases by county on its strangles page; in October 2026 it listed, among others, cases in Marion County, Florida, and Jefferson and Dane Counties, Wisconsin.

In the UK, the HBLB code says there are no legal notification requirements, advises informing the national breeders' associations, and notes that under the Rules of Racing trainers must report likely or confirmed strangles to the BHA. The Surveillance of Equine Strangles (SES) network counted 383 laboratory-confirmed cases by late October 2025, against 270 in 2024 and 217 in 2023, and a UK annual average of around 300. Redwings reports that at least 61% of UK regions had a strangles diagnosis between 2015 and 2019, and the BHS points to Strangles Awareness Week, held every May. Even without a legal duty, the BHS list still asks you to tell everyone your horse met in the last three weeks.

How do you prevent strangles at your barn or yard?

The best strangles prevention is keeping every new horse apart for at least 3 weeks with daily temperatures, screening with a blood test, limiting contact for horses back from shows, and not sharing water at shows; a vaccine adds to that but doesn't replace it. The consensus statement says new arrivals should be isolated for at least 3 weeks, Tufts says at least three weeks and Maine says three weeks. For your own horses coming home from a show, Merck's professional chapter names restricted contact or isolation of resident horses who have been exposed during travel to shows, without giving a period. Other sources give other periods for new arrivals:

Given the incubation ranges above, three weeks is the floor we'd use. The HBLB code pairs the 3 to 4 weeks with daily temperature monitoring, and the Dick Vet sets 14 days as its minimum. A blood test on arrival and again two weeks later, as described above, is the screening the consensus statement describes. Owners want it too: in a 2016 Redwings survey, 1,600 horse owners (80%) said they'd prefer a yard that screens new horses. Our guide to new horse records and the new horse checklist cover the paperwork side of an arrival.

At shows, Redwings advises taking your own water, because shared tanks are especially high risk, and letting your horse nibble a haynet rather than graze. After an outbreak, clean before you disinfect: the consensus statement says to remove organic material with a foaming soap first, then soak surfaces in disinfectant, because chlorine compounds and quaternary ammoniums don't work in the presence of organic material, and to avoid pressure washers. Pastures used by sick horses are rested for several weeks, or at least 4 weeks according to the University of Florida. In a shared barn, clear arrangements about who handles which horse do half the work; our guide to sharing care helps you set them up.