Last Updated on February 24, 2022 by Allison Price
Improved management, vaccines and tests might help stop the spread of this deadly disease
Strangles. This name brings to mind images of horses suffering from strangles. This is exactly what is happening with this disease, at least in its advanced stage. The force doesn’t come from outside, it comes from within the horse’s lymph glands. Infectious bacteria can infect these glands and cause abscesses, which swell to the point that they explode into thick yellow-green pus from below the jaw or the nostrils.
Although strangling horses is rarely fatal, it can be very painful and debilitating. Horses may miss weeks of work due to strangles. It’s also highly contagious and spreads quickly from barns to farms. It can also survive on horses, making it difficult to control outbreaks.
Researchers are making great strangle research. Improved diagnostic tests, vaccines and management techniques could reduce the risk of outbreaks. This would have positive financial and health consequences.
Streptococcus equi: a Havoc-Wreaking Pouch-Dweller
Strangles have been known since the Middle Ages when it was first described in a 13th century text. Andrew Waller, BSc and PhD, chief of bacteriology at Newmarket’s Animal Health Trust (AHT), U.K., said that it was intractable at the time. Napoleon Bonaparte I, the French emperor of 19th century France, ordered strangles-recovered horses to his cavalry. He was well aware that all horses would get the disease and that the best way to ensure healthy horses on the battlefield was for them to have temporary immunity and had already survived.
Streptococcus subspecies bacteria can infect horses by settling into the lymph nodes of the neck and head, causing painful and swollen abscesses. Horses often become depressed, irritable, and lose their appetite. Many horses experience less severe symptoms or none at all. Waller says that clinical signs can last up to four weeks and are fatal in less than 2% of cases. Sometimes, “metastatic” strangles can develop, which can cause abscesses in the other parts of your body. These are more likely to lead to death.
Research suggests that horses who have been exposed to an S. Napoleon understood that horses who have been infected with S. Some horses can become carriers and carry the bacteria in their guttural pockets, which is a small cavity at the back. They appear perfectly healthy. Waller states that these horses can spread the disease agent silently anywhere they go, potentially for the rest of the horse’s life.
Strangles can be slipped by veterinary inspections because of its carrier status, according to Richard Newton, AHT director for epidemiology and disease surveillance, BVSc., MSc., PhD., FRCVS. One horse may have been freed from strangles a decade ago, but he might board a plane to infect other horses in the country’s quarantine area, infecting new cases in another country. Although it might seem extreme, this scenario is likely to spread the disease today through the movement of carriers horses.
Newton states that there is evidence to support this. Waller’s team has done genome studies on hundreds upon hundreds of isolates around the globe, providing crucial information about the spread of the disease. He adds that it is clear from the data that the organism traveled around the globe almost certainly with horses as the carrier state.
He says, “It is very widespread and it doesn’t discriminate.” It’s not a disease that affects only high-level horses and working equids. It can be found in all races. It’s not on the World Organization for Animal Health’s current list of recognized diseases, so it is not subject to pre-movement testing for international commerce. That would be a great change.
Scientists have perfected S. thanks to genomics research funded in part by The Horse Trust, an U.K-based equine charity. The Horse Trust has been funding equi screening tests over the past 10 years. To detect antibodies against bacteria in horse blood serum, they use enzyme-linked immunosorbent (ELISA) testing. They can also test S. equi can be detected in nasopharyngeal swabs and guttural pouch washes. equi DNA) as well as culture
They make it easier for vets to detect carriers and treat affected horses before they travel. Newton says that the United Arab Emirates has recently established a screening program to screen horses for import. This successfully blocked carriers and may have prevented new outbreaks.
Horses today often have exposure to or contact with other horses. Their owners are often busy and have a hectic schedule, trying to balance work life and horse life. Today’s horse owners are aware of their horses’ health and can spot early signs of disease. Ashley Boyle DVM, Dipl., believes that early detection and prompt testing are crucial. ACVIM is an associate professor of medicine at University of Pennsylvania’s School of Veterinary Medicine in Kennett square.
She says, “People know their horses well enough that they pick up strangles before they get to the abscess stage.” This helps to catch it early and prevents it from spreading.
Boyle states that managing strangles and preventing them from spreading to other horses requires significant biosecurity efforts. If owners are relying on guesswork, they don’t have the time or resources to invest in such efforts.
She says, “It can be difficult to get people to follow our biosecurity recommendations – and that is understandable.” “The sooner we can get a diagnosis, the more people will be willing to comply.
Boyle’s clinic boasts its own lab, which can run the most recent PCR test in as little as a few hours. She adds that clinics without in-house laboratories can receive a 24-hour turnaround using FedEx and UPS.
Boyle says, “Unfortunately, much can happen in 24hrs if these biosecurity measures aren’t put in place.”
In collaboration with University of Pennsylvania bioengineers, a new study could yield ultrafast field results that bypass the need to use a laboratory. The loop-mediated isothermal amplifying (LAMP), which is currently used to detect human infectious diseases in third world countries with slow mail services, could be used to diagnose strangles even before the veterinarian leaves the farm. Boyle states that if the technology works, we might be able to get the results down to 30 minutes.
Antibiotics: Are they safe?
Veterinarians have suspected for years that strangles could be worsened by antibiotics, spreading the disease to the horses’ bodies. Boyle claims that scientists have disproved this theory since 2007.
However, antibiotics are not the best choice to treat all cases of strangles. It all depends on the individual situation, according to our sources. Boyle says, “Certainly we are giving antibiotics to strangles more generously than we used too, but that doesn’t mean we’re giving it away freely.” There are many issues to be aware of.
Antibiotics, for example, can slow down the healing process, especially if there are already abscesses. She says, “If you stop an abscess maturing (by treating it with antibiotics), it won’t drain even if it is treated surgically.”
Boyle suggests that it could also affect long-term immunity. However, there is no evidence to support this. She says, “Our experience shows that horses who are given antibiotics to treat their strangles do not seem to be protected against the disease.”
Boyle says that some owners give up on antibiotics too soon, either because it is difficult to administer the medication or because their horses seem better. This can result in antimicrobial resistance, which means bacteria becomes more resistant to drugs, greater disease spread and horses getting sicker over time.
Boyle states that there is a risk of giving the horse a false sense protection from antibiotics. People think that if their horse is exposed they can just give them antibiotics for a few more days. But this doesn’t work.
It is best to treat abscesses first in an average case. Boyle states that depending on the animal’s condition, you may want to keep them comfortable and provide supportive care with nonsteroidal anti-inflammatories. Make sure he can swallow and be aware of prolonged high fevers or dehydration.
She says that antibiotics may be necessary if the horse is ill. Some complications, like Type III hypersensitivity to strangles (a type of allergic reaction), require both antibiotic and nonsteroidal treatment.
Boyle and fellow researchers recently published updated guidelines for antibiotic use in strangles cases in a new consensus statement (https://doi.org/10.1111/jvim.15043) issued by the American College of Veterinary Internal Medicine.
Vaccines: Still Confusing
Strangles vaccines were developed by Percival Bazeley, an Australian veterinarian who vaccinated horses prior to shipping off to war. This was a revolutionary idea: Percival Bazeley “gently killed” an S. strain. Waller says he injected the vaccine intramuscularly into horses and equi. Side effects of the vaccine included painful and unsightly abscesses at injection sites.
Today, veterinarians in Australia and North America have access to better vaccines that they can either administer intramuscularly or intravenously. They require boosters, which are a series of three vaccines administered two weeks apart. Then, they must be repeated. These vaccines have low success rates and can lead to complications like abscesses (in case of IM injections). Although they now have access in Europe to live attenuated vaccines that they can inject into the upper lips, Newton says it is still not very popular with owners because of its poor efficacy.
All these vaccines pose a serious problem at a global scale: they cause positive screening tests. While owners may want to protect their horses, vaccines could be detrimental to the overall goal of protecting horses around the world.
Newton states that vaccines “trick the tests” and “(which) don’t distinguish between a vaccinated or nonvaccinated horse.” This is crucial when trying to eradicate or control disease.
Waller, a leader in genomic research at the AHT, and supported by The Horse Trust have created a new vaccine. However, it’s more effective than 80% in field tests and is not detected in screening. Innovative technology targets specific proteins within the S. The vaccine is based on innovative technology that targets specific proteins in the S. Newton states that vaccines that complement our diagnostic tests but do not interfere with them can help eradicate infections.
Waller believes that the vaccine could be on the European market by 2020.
Biosecurity: Wash, Change, Isolate
Streptococcus equi is a survivor. It is probably still here after hundreds of years. It can’t survive on horses for very long, but it can live for days on equipment, people, and even extreme cold or water.
Boyle says that it is crucial to distinguish between what’s dirty and what’s clean. She says sick horses and the equipment used to care for them (including human clothing) are “dirty” and that healthy animals should be avoided. Handlers should change their clothes and wash exposed skin and hair.
Waller and his colleagues recommend a “traffic lights” color-coding system for owners to deal with outbreaks. All sick horses and equipment should be marked red All healthy horses and equipment should be green. All exposed horses, even those that are healthy, should be yellow. Check all horses’ temperatures at least twice daily. If a horse’s temperature increases in yellow or green, it should be switched to the “red” group with its equipment.
Boyle believes that while this sounds great in theory, it is not easy to convince owners. She says that finding the space to separate the animals is the most difficult part. You can have one barn, one aisle and separate paddocks for each group. This will ensure that the horses don’t touch their noses. I help clients see the bigger picture. Even in small spaces, there are always solutions.
She recalls, among other things, a farm with 40 horses whose horses were exposed. However, the owners handled the situation well. She says that the horses were young and likely never had been exposed. This made them extremely vulnerable. It was also a warm and wet spring, which made it ideal for disease spread. We maintained biosecurity by making the barn the unclean area and the paddock clean. Also, we changed clothes and equipment between the two areas. We were able to reduce the spread to five to six horses, instead of forty.
It is the most common equine infectious disease. Despite all research efforts, strangles still plagues our fields and barns, causing problems for horses’ welfare as well as our pockets. S. can easily be spread by long-term, silent carriers while they travel. In unprotected areas, equi spreads quickly. Researchers are working to develop better vaccines and detection methods thanks to science and technology. Researchers hope to stop strangles from spreading by combining better understanding and compliance with recommendations.
Waller states that it would be impossible to eradicate the disease completely. “But the future looks really bright for finally starting to kick the disease and reducing how many horses are affected each year.”