Strangles is a highly contagious bacterial infection caused by Streptococcus equi subspecies equi that commonly affects young horses. It primarily causes fever and swelling of the lymph nodes in the head and neck. While most horses recover without complications, the disease can spread easily through nasal discharge from infected or carrier horses. Proper outbreak management includes isolation of sick horses, thorough disinfection, and vaccination to help control spread.

1. Understanding Equine Strangles
Christina L. Garloff, DVM
Equine Veterinary Associates, Inc.

2. History
First reported in 1251
Highly contagious
 Young horses most commonly affected
Recurrence at farm common
Most commonly diagnosed contagious disease worldwide
Cause
 Bacterial infection with Streptococcus equi subspecies equi (S. equi)
Location
 Usually affects the upper airway and lymph nodes of the head & neck,
but can be seen in other portions of the body

3. Clinical Signs
 Common:
 Fever (> 101.5°F)
 Anorexia, depression, difficulty swallowing
 Nasal discharge
 Enlarged submandibular lymph nodes
 Purulent nasal discharge
 Less common
 Enlarged retropharyngeal lymph nodes
 Guttural pouch infection-Empyema
 Enlarged lymph nodes on other portions of the head

4. Complications
 Most recover without complication
 Infection in other parts of the body
 Metastatic infection or Bastard Strangles
 Strangulation of airway
 Tracheostomy
 Immune mediated disease
 Purpura Hemorrhagica
 Muscle disease
 Decreased milk production in mares

5. Transmission
 Nasal/abscess discharge from infected horse
 Days to weeks
 Nasal discharge from asymptomatic carrier
 Months to years
 Contaminated environment
 Water-over 1 month, ground/bedding variable
 Contaminated equipment &/or handlers
 Buckets, feed tubs, grooming equipment, stall cleaning supplies, tack, clothing, other
animals

6. Diagnosis
 Clinical signs highly suggestive
 Culture of discharge
 PCR nasal swab
 Start shedding a few days after fever onset
 Intermittent for several weeks
 4-50% of horses on recurrent farms are carriers
 Months to years
 Blood titer-rise in levels when infected

7. Treatment
 Antibiotic therapy remains controversial
 Needed for complicated cases
 Anti-inflammatories for pain/fever
 Hot pack affected area
 +/- drawing agent (Ichthammol, etc.)
 Surgically lance when mature
 Soft feed if throat is sore
 Isolation from other horses!!

8. Outbreak Management
 Horse movement in and out of stable should stop
 Monitor temperatures twice daily
 Isolate at first sign of fever
 Contagious 1-2 days after fever begins

9. Outbreak Management
 Create three separate groups
 Clean horses with no exposure
 Separate area & separate caretakers & equipment
 Daily care should be first
 Exposed horses
 Infected horses

10. Outbreak Management
 Infected horses
 Use protective clothing
 Care for last
 Use dedicated equipment
 Thoroughly disinfect equipment
between horses
 Thoroughly disinfect hands and
shoes between horses
 Disinfect water buckets daily
 Waste from infected horses should
be isolated & disposed of separately
 Rest exposed turn-outs/arenas
minimum of 4 weeks
 Three consecutive negative PCR
swabs (at least one week apart) for
each horse before returning to
general population

11. Vaccination
 Does not guarantee disease prevention
 Intramuscular route
 High rate of vaccine reactions
 Approx 60% effective
 Intranasal route
 Current recommended vaccine
 Initial 2 doses, 2-3 weeks apart-protected 1 month after
second dose, annual booster
 Not recommended during an outbreak
 Recovered horses often develop immunity for 1 year
or more

12. Preventative Measures
 Require current health certificates for all new horses
 Obtain Strangles history/require negative PCR test before allowing on property
 Consider vaccination requirement before arrival
 Quarantine new horses for a minimum of 3 weeks before allowing in general population
 Monitor temp daily
 Each horse should have a dedicated water bucket that is disinfected regularly
 Minimize exposure to other horses/supplies at shows
 Pastured horses should be grouped by age & risk level

13. Questions?