You definitely don’t want strangles in your barn.  

While it has a very low fatality rate, strangles—caused by the bacterium Streptococcus equi subspecies equi—can make horses, donkeys, and mules painfully sick, said Marta David, DVM, resident ECEIM at the Vet-Agro Sup, part of the Veterinary School of Lyon, in Marcy L’Etoile, France. David described the disease and how to manage a strangles outbreak during her presentation at the 29^th Equita Lyon, Le Salon du Cheval, held on Nov. 1, 2023, in Lyon, France. 

Infected horses usually have a fever, nasal discharge, and swelling under the jaw in the submandibular lymph nodes—classic clinical signs that can last from three to eight weeks. In rare cases abscesses might form, which can affect the nervous and digestive systems, genitals, and/or the skin, and even become fatal. Horses younger than 5 years old with no history of exposure to the bacteria are at the greatest risk, she explained. 

Strangles enters the barn through an index horse, or an animal carrying and shedding the pathogen into the environment where it infects other equids, David said. Index horses are often silent carriers, appearing healthy but carrying an off-and-on infection. The incubation period—during which the bacteria can proliferate without causing visible signs—lasts from three to 21 days.  

Strangles in horses is highly contagious, typically infecting 100% of equids on affected premises, said David. Complicating things further, the strangles pathogen can persist for weeks in humid environments. As a result, outbreaks can last months, with accompanying quarantines, veterinary care, and strict biosecurity measures. 

When strangles hits a barn—or even if it’s hovering nearby—owners should take all the necessary precautions to keep their horses as healthy as possible and stables as clean as possible, said David. Here is a critical run-down of her recommended do’s and don’ts of managing a strangles outbreak in a barn.  

DO: 

• Involve a veterinarian at the first sign of disease.  
• Get a solid initial diagnosis of the first case using two tests: a polymerase chain reaction (PCR) and culture on a nasopharyngeal swab, taken via the nasal passage or directly from the abscessed lymph nodes. 
• Declare the outbreak to relevant authorities and surveillance programs (if applicable in your area). 
• Know how the S. equi bacteria spread:  
  • Through direct contact between horses; 
  • Through indirect contact—nasal discharge on clothing, hands, and equipment; 
  • Through airborne droplets such as cough; and 
  • Through shared water sources. 

• Know how long the bacteria survive: 
  • One to two days in the direct sun in a hot, dry environment; 
  • 34 days in a humid, cool environment; and 
  • Six weeks in water. 

• Create color-coded zones in your barn or on your property according to the resident horses’ infection status: 
  • RED: Horses with clinical signs and/or a positive diagnostic test; 
  • YELLOW: Horses that have had direct or indirect contact in the past three weeks with any animals having clinical signs and/or a positive test; and 
  • GREEN: Horses that have had no contact with sick or potentially infected horses. 

• Create a no man’s land between each zone, measuring at least 10 to 25 yards (10 to 25 meters) wide. 
• Change clothes and gloves between zone visits and use antibacterial soap and disinfectant on hands and equipment. Ideally, have different people working in different zones throughout the outbreak.  
• Take the rectal temperature of each yellow-zone horse one or two times per day and move that horse to the red zone as soon as the temperature goes over 100.4 F (38.6 C).  
• Maintain optimal ventilation within indoor zones to promote good respiratory health. 
• Moisten hay for sick horses to make it easier to chew and swallow. 
• Retrace all movement in and out of your stables in the two weeks prior to the outbreak to help identify the index horse and warn other owners of any outbreak risks. 
• Clean all surfaces (including inside trailers) with antibacterial soap followed by bleach or another strong disinfectant once the outbreak has ended, and air out for several days before introducing new horses. In a perfect world, barn owners should replace wooden surfaces, which tend to harbor pathogens, but because this is impractical, leaving horses out of any wooden enclosures for at least six weeks and exposing them to sunlight can help reduce their risk. 
• Compost used bedding far from stables and water sources for at least six months. 
• Leave pastures that have held sick horses empty for at least six weeks. 

DON’T: 

• Don’t forget this is a contact-transmitted pathogen! It can easily travel on people, equipment, and surfaces and can contaminate water. 
• Don’t move any horses off the property after a single case has been detected. This is the No. 1 mistake owners make, usually because people want to protect their own horses from the disease, David says.  
• Don’t close horses up in barns completely or block airflow in any way. Good ventilation is important for horses fighting upper respiratory tract infections, and S. equi bacteria are not transmitted through the air. 
• Don’t wash surfaces with high-pressure cleaners, which favor the suspension of bacteria in the air and diffuse the pathogen more so it can rest on surfaces that horses might come in contact with. 
• Don’t release isolation areas from quarantine until you’ve had a negative PCR and culture tests—from each horse two weeks after the end of the last clinical signs—even if that means six to eight months of isolation.  

Take-Home Message 

Prevention—especially through careful biosecurity when introducing a new horse into a facility or bringing horses home from an event—is the ultimate way to protect horses from strangles, said David. It is important to quarantine every horse that is introduced to a new location. Even if a horse farm experiences an outbreak, owners can go a long way in keeping infection to a minimum by following basic strangles management rules, such as those described.