Strangles is an acute, very contagious bacterial respiratory disease, mainly affecting young horses from 2 months to 5 years of age. The bacteria causing this disease is called Streptococcus equi. Initially, affected horses are dull, lose their appetite, and have an increased temperature. A thin clear discharge from the eyes and/or nose changes to a pussy greenish profuse discharge, a soft cough is common, and the lymph glands under the jaw become enlarged, hot and painful. These swollen glands can ooze serum, lose hair and soften before they rupture to discharge a thick creamy pus (rupture usually occurs 7 – 14 days after first signs of Strangles). Once the glands have ruptured, the horse usually appears brighter, the temperature reduces, appetite returns and nasal discharge reduces. The ruptured glands reduce in size and start to heal. Most horse recover fully; however a few develop complications. The glands can rupture internally and the horse breathes the pus into its lungs (leading to death or pneumonia); or the bacteria can invade the bloodstream and infect glands in other parts of the body (“Bastard Strangles”) leading to multiple abscesses and other problems. One of the more serious complications is purpura haemorrhagica – where the legs swell and small haemorrhages occur in membranes of the mouth, eyes, etc. This may also follow vaccination.
The bacteria can remain infective in the environment for up to 8 months, though more likely 2 – 4 weeks in NZ. Discharges from the nose and ruptured abscesses and droplets dispersed by coughing are rich in the bacteria. Most horse become infected directly from another horse, or indirectly from contaminated hands, equipment, utensils, feed bowls, rails etc., or instruments. It follows that prevention revolves around very good hygiene, isolation of infected horses, and disinfection of all areas and equipment that the infected horse has been in contact with. There is also a vaccine that helps the horses immune system to react against this bacteria invading its tissues. However, this is not a strong immunity and the horse can still suffer symptoms (although not as severely as it would have if not vaccinated) despite being vaccinated. The course of vaccinations involves 3 injections 3 weeks apart, followed by an annual inoculation. Talk to your vet about this.
Treatment of affected horses with antibiotics (penicillin is the drug of choice – ampicillin and oxytetracycline have also been used with success) early in the disease is effective in shortening the course of the disease and helping prevent spread throughout the body. Dose rates should be high enough to achieve this – your vet will know the recommended dose rates. Surgical treatment involves your vet draining the abscess with a blunt instrument (many vital structures are localised very near glands affected) very carefully, and not too early in the disease. Horses showing signs of Strangles should not be vaccinated (there is no benefit and the risk of purpura haemorrhagica is high).