Attention Equine Community
Strangles Outbreak

Aloha Y’all,

I am writing this letter to our entire Maui horse community to clarify, clear the air and explain what we are dealing with the current Strangles outbreak. As many of you are aware, we experienced our first confirmed case of Strangles back in September and since then, many more horses have been affected. I have attached a fact sheet put together by Dr. Patterson that further explains the infection and how it affects our horses.

Dr. Matchett, Dr. Patterson and I have had extensive conversations with our state veterinarians as well as specialists from the mainland and the manufacturers of the vaccines. We have been educating ourselves the best we can so we can educate you all and do our best to alleviate any more spreading of the infection. We have also met with Jess Cole, President of Maui Polo Club and Ken Miranda of Kaonoulu Ranch about the current status of active cases and their locations and what needs to be done to contain the spread and the future spreading of the infection.

Upon our lengthy discussions and recommendations from the state, it has been decided that Cowboy Polo will be cancelled this weekend. Manduke and the scheduled clinic is still on since all horses participating have been exposed and / or vaccinated appropriately. Please do not bring or introduce any new horses to the Polo facilities without verifying that they have been completely immunized for Strangles first. Verification will need to be provided to whomever is putting on the event.

We have changed our vaccine protocols, and these will be strictly enforced at all rodeo events and polo events including the 4th of July rodeo. It will be expected that any outside horse entering the grounds be able to present proof of vaccination by a licensed veterinarian. Acceptable proof of vaccinations are vaccine certificates from your veterinarian, or you may download the Makawao Veterinary Clinic App to your phone that will have the vaccine history of your horses at your fingertips to show for entry to the appropriate places. With the summer events that will be quickly upon us, it is mandatory everyone be brought up to date. If you are unable to present proof of vaccination from a veterinarian, you will be denied entry into events and even on the grounds. We have many visitors coming from other islands and many of us ship our horses to other islands for events as well. If we are unable to follow the proper protocols that are being enforced, it is important that everyone understand the ramifications if these protocols are not followed.

If the above protocols are not followed and there are additional confirmed clinical cases on Maui the State will step in and essentially quarantine Maui. This will prohibit horses from shipping out or coming in. As Strangles was deemed a reportable disease in 2017, this outbreak is being taken very seriously.

I cannot stress the importance of properly vaccinating your horses and taking the proper precautions from spreading Strangles further, this includes people caring for horses that have been infected and traveling to other pastures, barns, horses, etc… Because it is so highly contagious, the polo grounds are under quarantine until any horses showing clinical signs have resolved and the appropriate time frame has passed to clear the environment. At that point, all water troughs, buckets, trailers, stalls, pipe pens will have to be disinfected. Strangles can live in the environment for up to 3 days and water troughs for up to 30 days. Disinfecting the environment is best achieved by using a mixture of 1 ounce of bleach to 1 gallon of water.

The recommended protocol is a series of two intranasal vaccines, that can also be administered orally, 2-3 weeks apart for the initial vaccination and every 6 months after that. We are also enforcing the Flu/Rhino vaccine every 6 months as all these diseases are highly contagious. These vaccines must be given by a veterinarian in order to guarantee proper administration and handling. It is not mandatory that Makawao Veterinary Clinic be your vet for this, but it must be a licensed veterinarian. There is an intramuscular vaccine available, but it does 3 boosters and does not provide effective protection as quickly as the intranasal.

Please don’t hesitate to contact us with any questions you may have or to schedule an appointment.

Mahalo for Everyone’s Continued Support and Understanding,

Lizzie Immarino


What is “strangles?”

Strangles is caused by bacterial infection with Streptococcus equi subspecies equi (referred to as S. equi). The bacteria typically infect the upper airway and lymph nodes of the head and neck. The disease has been in the equine population for centuries, and was first reported in 1251. The infection is highly contagious in horse populations, particularly affecting young horses, and can recur on farms with previous outbreaks of the disease. It is one of the most commonly diagnosed contagious diseases of the horse, worldwide. The persistence of this infection on farms is multi-factorial. The bacteria can survive in water sources for over a month, but the primary source of recurrent infections is most likely asymptomatic carrier horses that can shed the bacteria to other horses for months to years.

How serious is it?

Most animals fully recover from strangles in two to four weeks. Although enduring immunity against re-infection is variable, in some equids it can last for years.  However, not all horses develop a protective immunity upon recovery.  Some horses, although they appear healthy, shed the bacteria in nasal secretions for a prolonged period and can infect nearby horses. Horses can die from strangles due to asphyxiation or “strangling,” as well as from other complications.

How common is strangles? 

Strangles is highly contagious. It can spread rapidly from animal to animal and is one of the more common bacterial infections of horses.

How does it spread? 

The disease is spread via nasal secretions (snorting, coughing, physical nose-to-nose contact) and pus from draining abscesses.  Nasal discharge from the infected horse is the largest source of contamination. Sources of infection can be nose to nose contact with an infected horse, sharing contaminated water buckets, feed tubs, twitches, tack and clothing and equipment of handlers who work with infected horses.

Once the horse comes into contact with a potential source of infection, it may take three to 14 days after exposure before the horse will show the first clinical sign of strangles (fever). Based on this information, a minimum isolation period for introduction of new horses to the farm should be 14 days. 

What about fields and barns?

  1. equi isn’t a hardy organism; it doesn’t persist well in the environment. While it’s possible to contract strangles from an infected horse’s pasture, it’s very unlikely.

What should I do if I have a strangles outbreak in my horses?

Contact your veterinarian, stop horse movement until the outbreak is resolved, and work with your veterinarian to determine the need for follow-up visits to check for bacterial shedding. 

What should I watch for? 

Typical clinical signs begin with mild lethargy, reduced feed intake, slight cough, nasal discharge and a fever. For adults a rectal temperature over 101.5 degrees Fahrenheit or for foals over 102.5 degrees Fahrenheit would be considered a higher than normal temperature or a fever.  

In most cases, a few days after the onset of fever and more mild signs, the lymph nodes swell and form abscesses around the throat, as well as in some cases under or around the base of the ear. 

At first, the nasal discharge is clear then becomes cloudy and whitish. After the abscesses have ruptured and drained into the nasal passages the discharge usually becomes purulent (thick white to yellow).  

Horses are often seen positioning their heads low and in an extended position in order to relieve the throat and lymph node pain.  

Some of the abscesses may rupture through the skin. Be aware that the pus from the nose and draining abscesses is highly contagious to other horses.

It is important to keep in mind that not all cases develop the “classic” abscess formation. Some horses may just develop a fever and be off feed for a few days.

Without complications recovery begins, in most cases, after abscesses drain or infection begins to be resolved by the body.  

The retropharyngeal lymph nodes (located deep behind the throatlatch) may also become enlarged and abscess. These will sometimes drain into the guttural pouches, which are air-filled spaces within the head that are an expansion of the Eustachian tubes. Guttural pouch infection and pus accumulation (empyema) are often the result of retropharyngeal lymph nodes that abscess and rupture into the guttural pouches. Guttural pouch infection may also occur from bacterial entrance through the pharynx (throat).

Anorexia, depression and difficulty swallowing may also accompany signs of infection.    

Though strangles is highly contagious and can affect many horses on a farm, most horses with infection recover without complication. Complications from the infection include spread of the infection to lymph nodes other than the head and neck (also known as metastatic infection or bastard strangles), immune mediated disease (such as purpura hemorrhagica), muscle disease and pain and lack of milk production.

Horses that develop complicated infection typically require antibiotic and additional therapies based on veterinary examination.  

How will my veterinarian know if my horse has strangles?

Clinical signs of strangles are highly suggestive of the diagnosis. There are three methods to confirm the diagnosis of strangles:

  • Culture of the bacteria from the nasal discharge or abscess
  • Polymerase chain reaction (PCR) that detects DNA of the  equibacteria
  • Blood test (serology) that measures a titer to a specific protein (SeM) of  equi.

Polymerase chair reaction (PCR) is a very sensitive test that detects bacterial DNA. PCR cannot tell the difference between live and dead bacteria, so is typically used in conjunction with culture. However, if consecutive PCRs are negative, the horse is unlikely to have strangles. Anywhere from four to 50 percent of the horses on farms with recurring strangles are asymptomatic carriers of the infection. Most horses will begin shedding (bacteria can be transmitted from nasal secretions to other horses) the bacteria from their nasal passages a couple of days after the onset of fever. Bacterial shedding occurs intermittently for several weeks. Some horses may continue to shed the bacteria for months to even years, serving a continual source of new infections on the farm. All diagnostic tests and treatment of affected cases should be done under veterinary supervision.

Is there a vaccine against strangles?

Yes, there are several different vaccines and they can be used to help protect horses from strangles.



Vaccination is one method for prevention and control of infection with S. equi. However, vaccination cannot guarantee disease prevention. With strangles, vaccination will likely reduce the severity of disease in the majority of horses that are infected. Available vaccines can be administered by intramuscular and intranasal routes. Improper administration of the vaccination can result in poor protection against infection and/or complications at the site of injection; therefore, administration by your veterinarian is recommended. The intranasal vaccination results in the best local immunity.

Vaccination of horses recently exposed to strangles (that have high antibody levels) may result in purpura hemorrhagica. Purpura hemorrhagica is caused by an over-active immune response within the horse, which can result in limb swelling, swelling of the head, and small hemorrhages on the gums. Vaccination is only recommended in healthy horses with no fever or nasal discharge.

How can I minimize the risk of strangles at my facility?

  • Have a biosecurity policy for people and horses coming onto your operation, and avoid contact with horses of unknown health status or those that are ill.
  • Don’t overstock your equine facility.
  • If new horses are introduced, request a statement by a veterinarian regarding their health status including any recent exposure to contagious diseases. If there is any history of strangle disease or exposure to other horses with strangles consult your veterinarian regarding options for testing to determine if the horse is shedding Strep. equi. Keep newly arrived horses isolated for a few weeks to observe them for signs of illness.
  • Personnel attending to horses must take great care not to move from isolated horses to the other horses on the establishment, without taking appropriate precautions.
  • Don’t share tack, feed tubs, water containers, trailers, pens or stalls used by horses of unknown health status.
  • The organism is not thought to have extended persistence in the environment, however the exact duration of persistence is not known. Surfaces that are nonporous can be cleaned with soap and water, rinsed and then disinfected. Consult with your veterinarian regarding how best to disinfect surfaces in an equine facility. Special attention should be paid to the water containers that may have been contaminated with pus from ill horses.
  • Horses with a history of strangles can be tested to determine if they are shedding Strep. equi. Ask your veterinarian about the need for such testing of new arrivals.

Management of an Outbreak 

The first and most important thing to remember in a suspected outbreak of strangles is to involve your veterinarian right away to determine the diagnosis and the best control practices for your particular farm. Strangles is a reportable disease in some states, and the state veterinarian may need to be notified as well. Movement of any horses on or off the farm should be stopped, and new horses should not be introduced. Take the temperature of all horses on the farm twice daily. Normal rectal temperature is 99 to 101.5°F. Monitoring the rectal temperature and isolating horses at the first sign of fever is one of the most effective ways to stop the spread of infection. Infected horses can transmit the bacteria to healthy horses one to two days after they develop a fever.

An isolated area should be set up for horses with fever and any other signs of illness (nasal discharge, etc). Extreme care should be taken not to mix horses with infection and horses exposed to horses with strangles to unexposed horses.

Ideally, three groups of horses should be created:

1)      Infected horses

2)      Horses that have been exposed to or contacted infected horses and

3)      Clean horses with no exposure

Unexposed horses should be kept in a “clean” area, and ideally should have separate caretakers, cleaning equipment, grooming equipment, water troughs and pasture. People and equipment can transfer the infection from horse to horse. Extreme care, handwashing and disinfection of supplies must be observed by everyone involved. If different individuals cannot care for infected and healthy horses, then healthy horses should always be dealt with first.

  • Dedicated protective clothing such as boots, gowns or coveralls and gloves should be utilized when dealing with infected horses.
  • Work with infected horses last if the same personnel cares for the entire farm.
  • Use dedicated equipment for infected horses (pitch forks, rakes, tack, etc.).
  • Thoroughly disinfect equipment between horses (Read the label instructions on disinfectants to be sure they are used at the correct dilution and are active against S. equi).
  • To disinfect stables and vans, remove all manure and debris first. Soak all surfaces with liquid disinfectant or steam treat the area and allow to dry.
  • Disinfect water troughs daily that are used by infected horses.
  • There is no evidence that S equican survive for long periods on pasture.
  • Pastures used to house infected horses should be rested for 4 weeks.
  • Manure and waste feed from infected horses should be composted in an isolated location, and not spread on the pastures.

A serious challenge when dealing with an outbreak of strangles is identifying the horses that are carriers of the bacteria but are not showing any signs of illness. Ideally, all horses on the farm should be tested for strangles. Use of the bacterial culture and PCR, combined identifies carriers with a 90 percent success rate. Nasal pharyngeal swabs or washes can be done to sample the horses for infection. The washes improve the chance of identifying carrier horses. Additionally, all sick horses should be tested three consecutive times and be negative all three times before being put back with healthy horses. Previously infected horses can shed the bacteria for weeks to months, or even years in rare cases, which is why three negative test samples are recommended prior to reintroduction to the healthy herd. For the most accurate diagnosis of carriers and horses without obvious clinical signs, upper airway and guttural pouch endoscopy can be performed.  This procedure allows for identification of infections that can develop in the guttural pouch, and culture of that area.  Although disinfection, isolation procedures, and diagnosis can be costly; they are certainly cheaper than additional outbreaks on your farm.

Additional Preventative Measures 

Here are some additional suggestions for reducing your horse and your farm’s risk for infection:

  • Require a current health certificate for new horse arrivals on the farm.
  • Ask owners of new horses about a history of strangles and consider testing new horses to see if they are shedding the bacteria.
  • If feasible, quarantine new arrivals for 2 to 3 weeks and monitor their temperature.
  • All horses should have individual water buckets that are routinely disinfected.
  • If shared water troughs are utilized, they should be routinely disinfected.
  • When traveling to shows, minimize your horse’s exposure by bringing your own feed, buckets and equipment. Minimize use of shared stalls or pastures at show grounds.
  • If horses are pastured together, group them according to their age and risk level (for example, all weanlings together, all broodmares together).

Reducing your horse’s exposure to unknown horses and utilizing routine disinfection measures will decrease the chance of infection with strangles. If your farm does have an outbreak, isolation and containment of sick horses will help reduce the spread of infection.