Strangles:

Synonyms: Distemper, Infectious adenitis

• It is an acute infectious disease of equines characterized by catarrhal inflammation of URT with suppuration and abscessation of the associated lymph nodes.

Etiology:

• Streptococcus equi
• Gram +ve coccus
• Bacteria is very resistant and may remain alive for several months in purulent discharges.
• Fresh exudates can be sterilized by 5% cresol or 5% NaOH or heating at 90°C.

Epidemiology:

• Disease was widely prevalent in previous decades but of late, this has receeded to a greater extent.
• Horses suffer much more severely than donkeys or mules.
• Young horses within age group of 6 months to 36 months are most susceptible.
• Naïve or non-immune horses in a population have a high risk of infection, with morbidity rates potentially reaching 100%.
• The disease spreads quickly in environments where horses are housed in close proximity, such as stables, riding schools, and equestrian gatherings.
• Recent research has highlighted the extent of the problem within Ireland, estimating that over 40% of horses in Ireland have been exposed to this disease and may be chronic carriers of infection.
• It is estimated that up to 10% of horses may die due to complications of severe infection.
• Furthermore, up to 10% of affected animals may develop a chronic carrier state which results in intermittent shedding of the contagious bacteria.

Transmission:

• Nasal discharge of the infected animals is most important source of disease transmission.
• Ingestion of contaminated materials
• Droplet infection is also possible.
• Disease may be transmitted by stallion through copulation or to foal during suckling
• Transmission also takes place from fomites; e.g. feeding utensils, buckets, etc.

Pathogenesis:

Clinical Findings:

• Incubation period ranges from 2-5 days.
• High rise of temperature, profound depression
• Animal reluctant 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
• Inflammatory swelling of submaxillary lymph glands
• Formation of abscess in lymph glands which burst out releasing large quantities of thick yellowish or white or creamy pus.
• Bronchopneumonia results due to extension of infection from guttural pouches.
• Horse may stand with an outstretched neck to assist breathing and relieve lymph node pain
• Difficulty swallowing and breathing may occur due to the enlargement of lymph nodes
• Constipation followed by diarrhoea
• Scanty urine with increased album
• Purpura haemorrhagica may develop in a small number of horses 2-4 weeks after strangles

PM Findings:

• Edema and congestion of nasal mucus membrane
• Abscess formation in pharyngeal and submaxillary lymph nodes.
• Empyema of guttural pouch
• Changes in pleura and pericardium.

Diagnosis:

• Based on clinical findings and PM findings
• Isolation of streptococcus equi in affected horses.
• PCR testing
• Hematology: Increased neutrophil
• Immunodiagnostic test: ELISA, Passive HA

Differential Diagnosis:

1. Glanders:

• Nasal discharge is usually thick, sticky, yellow-green
• Multiple nodules/ulcers in nasal mucosa
• Disease progress slowly and often fatal if untreated

2. Equine influenza:

• Sudden high fever, dry hacking cough
• Rapid spread; no lymph node abscesses

3. Equine viral arteritis (EVA):

• Conjunctivitis,
• Edema of limbs/scrotum,
• Serous to mucopurulent nasal discharge, but lymph node abscesses uncommon.

4. Equine Herpesvirus-1/4 (EHV-1/4) respiratory form

• Pharyngitis, sometimes neurologic or reproductive signs
• Lymphadenopathy less suppurative

Treatment:

• Since the organism is gram +ve, penicillin is the drug of choice.
• Crystalline penicillin @ 10 million units is given through IM route
• Drugs like tetracycline may also be tried @10 mg/kg, b.wt.
• Pus materials from nose, eye, etc. should be carefully mopped with antiseptic solution.
• Benzathine penicillin (30 000 IU per kg IM q 2 days), or feed supplementation with low levels of tetracycline (60–80 ppm feed) are very effective in preventing or stopping an outbreak.
• Supportive therapy of strangles includes twice-daily cleansing of draining sites and nostrils, application of fly repellants, and provision of high quality soft, moist feed.
• Guttural pouch infections may require irrigation with surgical antiseptic or penicillin solutions.
• Horses that develop purpura hemorrhagica includes corticosteroids to reduce leukocytes response.
• Edematous legs should be bandaged.
• Blood transfusion may be indicated in cases with anemia or thrombocytopenia.

Control Measures:

• Due to contagious nature of disease and rapid spread, animals with clinical signs should be isolated immediately.
• Contaminated premises should be thoroughly disinfected. Beddings should be burnt.
• Animals with contact may be immunized passively by injecting immune serum SC at dose of 200-300 ml for few days consecutively.
• Freeze dried vaccine may be given to susceptible animals for active immunization. Foals upto 6 months of age; 4 injections at 10-14 days interval consisting 1ml, 2ml, 4ml, and 8ml, through SC or IM route.
• Foal upto 6 months to 2 years of age: 4ml, 8ml, 16ml SC or IM at 10-14 days interval.
• Regular temperature checks should be performed every 12 hours to detect feverish animals and separate them to prevent spread.
• Newly purchased horses should be isolated for 4 weeks before introduction into herd.
• Good hygiene and biosecurity in the yard are vital to minimize infections. Stressors like overcrowding should be avoided.
• Maintaining disinfection of equipment and stables between horses to minimize spread of disease.