“Strangles” is a bacterial infection, caused by Streptococcus equi that affects the respiratory tract. Infection is by inhalation or ingestion of the bacteria from an infected horse.
Signs appear 3-12 days after exposure and include some or all of the following: –
- Dull, depressed, with loss of appetite due to elevated temperature and pain.
- Large swellings under and/or behind jaw which usually rupture releasing thick yellow pus.
- Thick yellow / green pus from nose, sometimes blood tinged.
- Occasionally pneumonia may develop, particularly in young, old or debilitated animals
- Rarely abscesses may be located in the abdomen causing colic, peritonitis, hepatitis, chronic weight loss or death.
The risk of death from strangles is estimated as <5%.
- Purpura haemorrhagica = severe swelling of limbs, serum oozing from skin, sloughing of skin tissue.
- The infection may become localised in the guttural pouches [pouch of eustachian tube] resulting in intermittent nasal discharge or no signs but causing a “carrier” state remaining infectious to other horses.
- Some horses may regurgitate food from their mouth due to damage to the throat and swallowing reflexes.
- Occasionally muscle wasting, particularly along the back-line is also seen.
Clinical signs usually resolve in 3-6 weeks but more than 50% of cases remain carriers for longer than this time due to the bacteria remaining in the guttural pouches. Recent infection may result in immunity for several years but approx. 25% remain susceptible to re-infection within 6-12 months.
Treatment involves the administration of penicillin, anti-inflammatories and mucolytics depending on the location and severity of infection. Hot packing of abscesses helps promote rupture and drainage. Recovery to previous performance may be prolonged and some horses may become carriers and are a potential source of infection to others without still showing signs themselves. In some of these carrier horses nasal discharge may be intermittent and a focus of infection found in the guttural pouches [pouch on eustachian tube between throat and inner ear] or in the lungs. Others have no apparent signs so scoping and repeated cultures of the guttural pouches are very important in detecting chronic shedders.
Strep. equi survives short period of time in the environment, unless protected by moisture. Controlling moisture is important regardless of what disinfectant you use to clean feed-bins, trucks, stables, head collars, hands etc. Under moist conditions the bacteria may survive in the environment for up to 2 months.
New horses to the property should be isolated for 2-3 weeks with close monitoring for nasal discharge.
Vaccination does not give 100% protection but vaccinated horses generally have far milder signs and recover quicker than non-vaccinated horses. The initial course involves three injections two weeks apart followed by boosters every 6-12 months depending on the risk in the area.
Tetanus and strangles vaccinations can be combined and are advised for all horses. Mares should be boosted 1-2 months before foaling to maximise the antibodies in the colostrum. Foals are often given a short-acting anti-tetanus injection at birth when they are most as risk. Foals < 3 months of age do not respond well to vaccination due to the immaturity of their immune system and interference from maternal antibodies, so vaccination is recommended after this age.
Control of an outbreak
Separate horses into three groups:
A: Infected and showing signs during past month.
- Penicillin as advised by veterinarian depending on severity of signs?
B: Horses that have been in contact with first group but not showing signs yet
- Monitor temperature twice daily and clinical signs for 10-14 days – treat any new cases and move to group A immediately.
- If no signs develop within 2 weeks vaccinate.
C: Horses that have NOT been in contact with above two groups
- Vaccinate or give boosters if previously vaccinated.
It is not only important to divide and monitor closely but also dangerous to just vaccinate all horses in the face of an outbreak. The condition known as purpura haemorrhagica mentioned previously [severe swelling of limbs, serum oozing from skin, sloughing of skin tissue] is a hypersensitivity reaction and may be precipitated by the vaccination of horses already infected and in the incubation stage before clinical signs are evident.
For further vaccine product information visit www.csl.com.
