The ever-present threat of strangles, Streptococcus equi, is a liability that needs to be dealt with promptly once it appears—before a mildly irritating case snowballs into a widespread epidemic. And, with a heavy show schedule, this highly contagious bacterium can spread like wildfire as horses travel throughout the circuit.
How It’s Transmitted
While all are susceptible, strangles is a disease most commonly contracted by groups of weanlings, yearlings, and horses less than five years of age. Transmitted directly as well as indirectly, it is a particularly difficult condition to control, especially in a herd situation once it gets going. If vulnerable, a horse that comes into contact with another who is either at the incubation stage, or has just recovered from an episode, or is a long-term carrier, is at high risk for infection. Indirect contact can be equally as insidious. Buckets, feed, walls, doors, grass, fences, and water troughs can all become a catalyst by which horses sharing stable or pasture environments are quickly infected.
The incubation period can be anywhere from four days to two weeks after exposure, depending on climate conditions or the level of stress to which a horse is exposed. Factors include prolonged travel time, crowded conditions, poor sanitation, inadequate nutrition, unsuitable housing, and introduction to a new environment.
Watch for these signs:
- Lethargy or depression
- Loss of appetite
- Enlarged lymph nodes under the jaw
- Thick, yellow nasal discharge
- Fever—102° F to 103° F
- Slight cough
- Trouble swallowing
- Abscesses which often burst and drain thick, yellow, highly contagious pus
- Standing with neck extended due to pain in the throat area
The general consensus is to establish a regular vaccination program, with boosters administered prior to periods of increased stress. Mares, stallions, and performance horses before the breeding and show seasons respectively, and horses who are about to be transported over long distances, would be the most likely candidates for immunization.
There are two types of vaccines available for controlling strangles: killed and live. In either case, your veterinarian should be consulted to determine or administer what is right for your situation.
The conventional treatment has been penicillin, a killed vaccine, which is administered through a series of intramuscular injections followed by an annual booster shot. Even though there is the possibility of local swelling or even an abscess forming at the injection site, the reaction is not usually serious and should subside within a few days. Although the killed vaccine does not provide complete protection, there is significant reduction in the severity of an outbreak, with fewer horses being affected, showing milder symptoms, and shorter recovery times for those who have been laid up.
The more recently-introduced live vaccine is administered intranasally twice at intervals of one to two weeks. Because it produces the local antibodies necessary to provide immunity, it is more appealing than its traditional counterpart, but, because it is a low-virulence organism, the risk of inadvertent contamination makes careful handling extremely important. It is strongly recommended not to administer other medications or injections at the same time as administering a live vaccine.
Identified carriers and horses with full-blown strangles should be moved to a quarantined area immediately, and all associated equipment should be disinfected (povidone iodine or chlorhexidine works best). Bedding should be burned or placed under a tarp to keep flies away, and pastures should be left idle for at least one month to ensure healthy regeneration.
As for the infected horses themselves:
- Keep infected horses warm and dry
- Provide softened feed
- Monitor temperature
- Apply hot compresses to abscessed lymph nodes to encourage drainage
- Flush with povidine iodine solution
- Horses should remain isolated for six weeks during recovery
There are opposing views among veterinarians as to whether or not antibiotics would help or hinder a horse in an advanced stage of strangles. Some vets believe that treatment can interfere with the immune system, delaying the healing process, and in some cases even predisposing the horse to bastard strangles, a potentially fatal strain of the disease.
It’s important to note that each occurrence should be handled individually. Based on the severity of the disease, the course of treatment will vary. Young horses, especially, who tend to be more susceptible, might need specific treatment should the infection progress to a critical state, which may be signaled by severe breathing or swallowing difficulties.
Most horses infected with strangles develop immunity once they have recovered. Nevertheless, the strangles organism can remain in an individual’s system for months or even years, and while it may no longer exhibit signs of the disease, it is possible for a once-infected horse to become a carrier. Therefore, before introducing new arrivals to your barn or herd, it is important to isolate them for a week to ten days of observation to ensure there are no symptoms and that their temperatures are normal. At that point, while it is wise to vaccinate, it is not mandatory.