Photos courtesy Weatherford Equine Medical Center.
This story originally appeared in the August 2009 issue of Barrel Horse News.
Strangles typically occurs in horses between one and five years of age. It’s caused by the bacteria Streptococcus equi, and in its most typical form causes abscessation of the lymph nodes under the jaw and/or throatlatch.
The first indication of Strangles is a high fever (103–105ºF), which usually occurs within three to five days of infection. The horse may be depressed, have nasal discharge, be off feed and have difficulty breathing due to the abscesses restricting the airways; however, mild cases of nasal discharge only may occur.
The abscesses usually rupture creating discharge that will persist for several days until the infection has been resolved. In addition to abscesses under the jaw and throat latch, Strangles can also cause sinus infections or abscesses of the superficial lymph nodes throughout the horse’s body including the groin, pectoral and eye areas.
The majority of horses develop a self-limiting form of Strangles and progress through fever, development of abscesses, rupturing and healing within six weeks.
If an abscess has not ruptured naturally it may be lanced to relieve pressure off the respiratory system and accelerate healing.
“In some cases we have to use ointments and hot packing to get the abscesses to mature so we can surgically open them up,” says Dr. Rob Franklin, of Weatherford Equine Medical Center in Weatherford, Texas.
Normal cases of Strangles are not treated with antibiotics.
“We isolate the horse and let it run its course,” he says, “but we will treat them for their fever and give them anti-inflammatory drugs to make them feel better so they’ll eat.”
Potent strains of the bacteria that lead to more severe disease states may require antibiotic treatment, especially if swelling around the throatlatch has put pressure on the respiratory system that could lead to the horse suffocating (hence the lay-term “Strangles” for the infection).
“The disease can cause so much pressure up around the throat latch area that they can’t move enough air,” Franklin says. “In these cases we may have to do a temporary tracheostomy, which is a hole in the wind pipe, so the horse can breathe. It’s a safe procedure and immediately stops the respiratory distress.”
A less common form of Strangles is Bastard Strangles, which occurs in the lymph nodes inside the horse’s body and usually in the abdomen. These abscesses are not readily identifiable, and by the time they are found, the horse can be in significant trouble. Abscesses can grow to the size of a basketball and can cause adhesions in the intestines where the intestines stick to the abscesses. The most common symptoms related to Bastard Strangles are colic and chronic weight loss.
Treatment of Bastard Strangles is very difficult and on a case-by-case basis. Most horses are put on courses of systemic antibiotics for more than 60 days to decrease the size of the abscesses. Surgical options are difficult and can include various techniques to allow for drainage or removal of the abscesses entirely.
Secondary Exposure and Purpura
Reportedly, 75 percent of horses that have been exposed to Strangles will develop long-term immunity to it. The remaining 25 percent may develop Strangles again later in life. Both groups of horses are still able to develop a secondary complication called Purpura Hemorrhagica if they become exposed to it again.
“Streptococcus bacteria, and especially the type that causes Strangles, provoke a very intense immune response which is why horses with Strangles get very high fevers,” Franklin says.
When the immune response becomes uncontrolled the body begins to damage itself and can cause tissue destruction and inflammation along blood vessels. This can lead to severe stocking up in the horse’s legs. This swelling can progress into massive tissue sloughing causing the horse to lose its skin on its lower legs, which can even lead to a fatal systemic reaction.
“This is a response from exposure to the bacteria but it doesn’t necessarily mean the horse is infected with the bacteria,” Franklin says. “We often see this in horses that have had the disease before and have been re-exposed to it. They don’t get the infection, but their immune system recognizes the bacteria and it goes haywire.”
This can occur from either natural exposure to the bacteria or through exposure from vaccination.
Horses with Purpura are treated with corticosteroids to suppress the body’s immune response to help minimize swelling and skin sloughing. Lower limbs are wrapped to reduce swelling, and the wounds are treated. Antibiotics are administered to treat the horse for secondary infections.
“Purpura affects a very, very small percentage of horses,” Franklin says. “It’s not common, but it’s something that we see and people need to be aware of it because it can be very problematic.”
Streptococcus equi is a highly contagious bacterium that is spread between horses by direct contact or by sharing feed or water troughs. It does not persist in the environment for long periods of time and can easily be removed by disinfecting and will usually be cleared from a horse stall within three days; however, it can survive on water sources such as troughs for up to a month.
“You need to have a constant source of the infection,” Franklin says. “If you have it on your farm, and you control the disease, then it will not stay on your farm. You’ve got to have a constant source of bacteria.”
Several Strangles vaccines are available; however, none are 100 percent protective, and all may present differing side effects.
“Every time we look at a horse to vaccinate, we look at the relative risk of that horse developing Strangles compared to the risk of using the vaccine,” Franklin says.
Risks include abscesses at the injection site of intra-muscular vaccines, mild cases of Strangles with intra-nasal vaccines and the risk of Purpura with all vaccines.
“The risk of them getting Strangles is higher without a vaccine than the risk of developing Purpura with the vaccine,” Franklin says. “You’re weighing the risks, and the risks are much higher for them to go to a barrel race and develop Strangles than it is for them to have a problem related to a vaccine.”
Vaccination is based on the age of the horse, prior exposure and potential exposure. If a horse primarily stays at home and does not come in contact with horses being shipped, it is unlikely that it would be vaccinated. Neither would a horse that has had a case of Strangles in the past.
Young, competitive horses that travel to events and horses that have a lot of contact with shipped horses, such as those on breeding farms, are more likely to require vaccination.
Vaccination frequency varies from six to 12 months depending on the horse’s movements. Horses that potentially could be exposed to Strangles, such as competitive horses, should be vaccinated at least a month in advance of exposure to enable the horse to develop a good level of immunity.
A quarantine protocol for new horses entering a facility can ward off an outbreak of Strangles. Keep new horses separate for a period of two weeks, so they can be monitored for signs of respiratory disease including Strangles, Flu and Rhino.
Transferring Strangles from one horse to another requires nose-to-nose contact, whether it’s passed directly between horses or via mechanical transfer such as bits, feed bunks, lick blocks and water troughs.
“If you are quarantining you can’t put a new horse’s bit in another horse’s mouth because that is effectively nose-to-nose contact,” Franklin says.
Managing an Outbreak
Strangles is most problematic on horse farms where there are horses of varying ages that are frequently transported on or off the property. During the first seven days of being infected and contagious, a horse may not show symptoms of the illness. As a result, they are often taken to barrel races and breeding farms, where they expose other horses to the disease.
Franklin believes that as soon as a horse is identified as having Strangles that management processes should be implemented to prevent spread of the disease to horses at the home facility and away.
“In my opinion,” he says, “it’s dangerous to let a wildfire burn, especially if you’ve got horses moving.”
In the past, many horseman have let Strangles run its course throughout entire herds without intervention.
“It’s one thing if you’ve got a group of yearlings out in the back 40 that are isolated from other horses, and you don’t have horses going into or coming out of that pasture,” Franklin says. “In that instance, the wildfire can potentially burn itself out and not cause any new fires. But you can still have some fatalities from the disease because not all of the horses will develop a mild form of the disease. Some of them may become respiratory-compromised, or they might develop Bastard Strangles or Purpura. To continue the analogy, if the disease is left to burn itself out, you still need to keep a close eye on the fire.”
The first step in managing Strangles is to team up with your veterinarian and set up a quarantine protocol to aid in determining where the infection came from and which horses have been exposed to it.
New horses to the premises are the first suspects when determining the source.
“Look at who is sick and ask yourself ‘Where did the disease come from?’” Franklin says, “because it’s not going to stay in the environment, so it’s got to have been brought in by a horse.”
Horses should be divided into three groups: those that are free of Strangles symptoms and have never been exposed to the disease, those confirmed with the disease and a suspect group of horses that have been in contact with the contaminated group. The three groups should be kept separate with the clean horses being kept as far from the other two groups as possible.
“That’s important because the clean horses can continue training, going to barrel races and doing those things that the owners and trainers are hoping to do with the,” Frankllin says. “It doesn’t have to shut down the whole operation. But if people just let the disease run its course and continue going to barrel races without quarantining infected horses, then they’re putting other horses’ health in jeopardy.”
The clean and suspect groups are monitored daily and have their temperatures taken and jaws checked for lymph node enlargement. Over a period of time, horses in the suspect group will be transferred into the clean group or the contaminated group.
Horses in the suspect group that develop a fever can be treated to prevent them from developing a full case of Strangles.
“The fever precedes the development of the abscesses,” Franklin says. “We can intercept those horses with antibiotics to keep them from developing the abscesses and to accelerate their progress into the clean group. It requires dedication, and people have to stay on top of their records, but there is a way to contain Strangles and stop it spreading all over the farm.”
One of the biggest challenges to containing Strangles is the Silent Carrier. A small percentage of horses are able to transmit the disease without showing physical symptoms of being infected with it.
The lymph nodes behind the horse’s jaw drain into the guttural pouch where the bacteria persist in a mucus concretion called a chondroid.
“They’ll walk around carrying the infection,” Franklin says, “but aren’t showing any fever, and the lymph nodes aren’t swollen. These horses can pass on the disease for as long as they are carrying the infection in the guttural pouches—which can be for years.
“This is problematic in horses that we don’t know their history like recipient mares and new horses to the barn. Typically, these horses are well vaccinated and de-wormed, but we just don’t know that they are a silent carrier, and they can be very dangerous to us in terms of transmitting the disease.”
A silent carrier is suspected when the source of the disease cannot be identified. To find the culprit a nasal wash is done on the horses and the samples tested for Streptococcus equi DNA via a Polymerase Chain Reaction (PCR) Test.
To offset the cost of testing large herds, the horses can be divided into groups of smaller numbers. Samples from within each group are pooled and tested. If a group returns a positive test, then each horse in the group is tested individually. If a group returns a negative test, another test is done to ensure that all horses are negative.
Once the silent carrier has been identified, the bacteria is removed from the guttural pouches via endoscopy.
“It can be tedious and time consuming, but it is very worthwhile,” Franklin says. “It pays for itself by keeping the horses healthier, in training and being able to compete. There are some farms that do it routinely, so that they can pick these horses up before they are introduced to the herd. For broodmares and recip mares where we don’t know the horse’s history, it is the prudent thing to do. At our barn, we screen our recip herd before we send them away to try to not send any disease out to the farms that take on the ET babies.”
Keeping Strangles A Secret
Trainers and breeding barns often try to keep outbreaks of Strangles a secret due to backlash from owners; however, transparency and planning for an outbreak is the key to containing the disease.
Owners should ensure that trainers and breeding barns are provided with the horse’s history regarding Strangles, including prior exposure and vaccinations.
“It’s not a disease of the premises,” Franklin says. “Once all the horses have gotten over it, the farm doesn’t have it anymore.
“It’s a tough situation for trainers and breeders to deal with it because they have to tell their owners about it. People need to understand that this is a disease that will occur, and that we have a plan to control it and minimize the effects of it in the future. I think even the most demanding horse owners can be understanding of the problem if a plan to control the disease has been identified and implemented.”
Competitive Horses and Strangles
Vaccination and quarantine can help keep competitive horses safe from Strangles. The horse should be well vaccinated before attending a barrel race. At the event, the horse should be quarantined as much as possible. Avoid nose-to-nose contact with horses from other barns through the bars of the stalls, on trailers and during warm-ups. Do not allow the horse to drink from communal waters or share feed bunks with horses the trainer is not familiar with.
About Rob Franklin, DVM, Diplomate ACVIM
Dr. Rob Franklin was practicing veterinary medicine in Florida during the Strangles epidemic of 2005. He is board certified in internal medicine with particular interests in infectious diseases, neonatology, inflammatory airway disease, emergency and critical care. He has participated in research in critical care, neonatology, neurology and cardiology.
Before joining Weatherford Equine Medical Center in Weatherford, Texas, he worked with leading horse doctors at the University of Florida, the Equine Medical Center of Ocala in Florida and the Goulburn Valley Equine Hospital in Australia.
Bridget Cook is an avid barrel racer and frequent contributor to Barrel Horse News. She resides in Poolville, Texas, will her husband, Nuce, and young daughter, Maggie. E-mail comments on this article to [email protected].