Strangles

Introduction

Strangles is highly contagious upper respiratory disease of equids worldwide. It is caused by the bacteria Streptococcus equi subsp. equi.and causes rhinitis, pharyngitis, lymphadenitis and myositis.

The disease often occurs where there a high numbers of young horses that are under stress, such as in racing yards. Most animals affected are under 6 years old though the disease is prevalent in all ages.

Transmission is via purulent exudate discharging from upper respiratory tract or from lymph nodes, which is then transmitted to the other horse by direct contact e.g. on stable doors, tack or feed buckets or by inhalation. A chronic carrier state of the disease can occur when bacteria is in the gutteral pouch. 

There will be 100% morbidity; 5% mortality in most cases as the disease is so contagious.

Clinical Signs

After infection, there is an incubation period 3 to 6 days followed by fever, depression, anorexia, purulent bilateral nasal discharge, swollen, painful regional lymph nodes, especially submandibular and abscessation and rupture of lymph nodes in severe cases. There may also be guttural pouch empyema.
Death can occur from pneumonia, breathing difficulties from swollen lymph nodes or purpura haemorrhagica(an immune-mediated disease).
Bastard strangle may occasionally occur, with abscessaation in many organs of the body. This will be difficult to diagnose as clinical signs are systemic and varibale, although history of having strangles in the normal form is presumptive.

S. equi may also be involved in cutaneous lesions.

Diagnosis

History and clinical signs are presumptive. Samples need to be taken via deep nasopharyngeal swab and sent off for culture. If present, you will see mucoid colonies with beta-haemolysis. Sugar fermentation allows differentiation of S. equi from S. zooepidemicus and S. equisimilis as the last two are commensals of the upper respiratory tract. PCR can be used to detect asymptomatic carriers.

Endoscopy of the gutteral pouch can be performed and samples taken to detect disease in here as this is more difficult to destroy and therefore stronger anitbiotics need to be prescribed.

Treatment and Control

In the case of an outbreak, Penicillin should be administered to the affected animal and to in-contact animals. If the affected animal is in the later stages of the clinical disease, such as an abscess is present then treatment with anitbacterials is not necessary.

Isolation of affected animals is required immediately. The yard needs to be shut and no animals are allowed in or out. Strict control needs to be enforced on all personnell in the yard and them made aware they are not to visit another horse or take their vehicle to other yards. Disinfection of all tack, stables, vehicles, boots and any other equipment that has come into contact with infected animals need to be performed.

Control measures to prevent the disease in the quarantine of all in-coming animals. It is important to try and reduce stress on the yard or within groups of horses turned out together and it is neccessary to avoid overcrowding and mixing different age groups.

References

Interview with Professors Josh Slater and Ken Smith providing an interesting insight into the pathogenesis, prevalence and possible prevention of Streptococcus equi infections in horses - listen to Strangles podcast

Brown, C.M, Bertone, J.J. (2002) The 5-Minute Veterinary Consult- Equine', Lippincott, Williams & Wilkin
Knottenbelt, D.C. A Handbook of Equine Medicine for Final Year Students University of Liverpool