It is an acute infectious disease of equines characterized by catarrhal inflammation of the upper respiratory tract with suppuration and abscessation of the associated lymph nodes.
Distribution
The disease was widely prevalent in previous decades but of late, this has receded to a great extent. The disease has been recorded from various countries of the world. The disease is unknown in Iceland and Argentina.
Aetiology
The disease is caused by Streptococcus equi, a gram positive coccus. It occurs in pure culture both in primary and secondary abscesses and in the nasal discharges. Streptococcus equi is very resistant and may remain alive for several months in purulent discharges. It is remarked, that an infected stable unless very carefully disinfected will remain infective for several months. Fresh exudate can be sterilized by 5% cresol or 5% NaOH or heating at 90° C.
Susceptible Hosts
This is essentially a disease of equines. Horse suffers much more severely than donkeys or mules. Young horses within the age group of 6 months to 36 months are most susceptible.
Transmission
Nasal discharge of the infected animals are the most important source of disease transmission. Organism usually get entry through ingestion of contaminated materials. Droplet infection is also possible. The disease may be transmitted by stallion through copulation or to foal during suckling. Carrier state is also possible. Carrier used to spread the infection. Transmission may also take place from fomites e.g. feeding utensils, buckets, etc.
Pathogenesis
The organisms on entry localizes in the pharyngeal and nasal mucous membrane and thus set up pharyngitis and rhinitis. Guttural pouches are filled up with pus. There is abscess formation in the adjacent lymph nodes. The infection may spread to liver, spleen and joints.
Clinical Findings
There is 30 to 100% morbidity and 9 to 10% mortality. The incubation period ranges from 2 to 5 days. There is high rise of temperature, profound depression, reluctancy to move, eat or drink. There is nasal discharge which ranges from serous to mucopurulent and finally purulent. Cough is evident due to pharyngitis and laryngitis. In most cases, there is inflammatory swelling of submaxillary lymph glands. Later on, there is formation of abscess which burst out liberating large quantities of thick yellowish or white or creamy pus. Recovery follows provided there is not further complication, The complications which may follow are:
- Suppuration of retropharyngeal lymph nodes.
- Abscess formation on mediastinal, bronchial and mesenteric lymph nodes.
- Development of purpura haemorrhagica.
- Bronchopneumonia due to extension of infection from guttural pouch.
- Vaginal infection following coitus with an infected stallion.
- Death due to secondary pneumonia.
Lesions
- Oedema and congestion of nasal mucous membrane.
- Abscess formation in pharyngeal and submaxillary lymph nodes.
- Empyema of the guttural pouch.
- Suppurative pneumonic changes.
- Changes in pleura and pericardium.
Diagnosis
This based on the following criteria.
- Epidemic nature of the disease in young horse.
- Swelling of lymph glands particularly of submaxillary lymph glands.
- Detection of Streptococcus equi in suppurative material by microscopic and serologic tests.
- Signs of leukocytes with neutrophils.
Differential Diagnosis
The disease may be confused with glanders. Therefore the following points should be viewed properly.
Points of Differences
| Strangles | Glanders |
| It is an acute nature of disease. Nasal mucosa shows inflammatory changes only. | It is a chronic nature of disease. Nodules, ulcers or ‘stellete’ are formed on nasal mucosa. |
| Lung lesions are not of tubercle like. | Lung lesions are tubercle like. |
| No ulcer or nodules are formed on the skin. | Ulcerative nodules are formed on the skin. |
| Pus material shows presence of gram positive streptococci. | Pus material shows presence of gram negative pleomorphic rods. |
Treatment
- Good care, adequate nursing, well ventilation of stable are to be provided.
- Affected one should be given easily digestible food substances.
- Since, the organism is gram positive, Penicillin is the drug of choice.
- Initially Crystalline Penicillin through intra-muscular route. Drug like Tetracycline may also be tried @ 10 mg/kg body weight.
- The pus materials from nose, eye, etc. should be carefully mopped with antiseptic solution.
Strategies
Treatment can be made based on clinical profiles and intensity of involvement.
| Clinical Profiles | Line of Treatment |
| Horse with early clinical signs | Use Penicillin G parenterally. |
| Horse showing lymph node abscesses. | Aspiration and drainage of abscesses. Parenteral antibodies (Penicillin), intravenous fluid and tracheostomy. |
| Horse previously exposed to strangles. | Further course of antibodies to prevent seeding of S. equi in pharyngeal lymph nodes. |
| Horse showing complication following strangles. | Penicillin and Corticosteroid parenterally. |
Control
The infected animals be kept in isolation.
Contaminated premises should be thoroughly disinfected. Beddings should be burnt.
In contact animals may be passively immunized by injecting immune serum subcutaneously at a dose of 200-300 ml for few days consecutively.
Freeze dried strangle vaccine may be given to susceptible animals for active immunization. Dose is as follows: Foal upto 6 months of age: 4 injection at 10-14 days of interval consisting of 1 ml, 2 ml, 4 ml and 8 ml through subcutaneous or intramuscular route.
Foal 6 months to 2 years of age: 4 ml, 8 ml, 16 ml subcutaneously or intramuscularly at 10 to 14 days interval. Foal 2 years of age: 10 ml and 20 ml subcutaneously of intramuscularly at 1 month interval.
Commercial bacterin consisting of whole cells and an acid extract of Str. equi 3 times at 10 days interval has been found to give good protection in 2-12 months old foal.
