Strangles in Horses: Etiology, Clinical Signs, Diagnosis, and Management

A comprehensive vocabulary review of key terms, clinical timelines, diagnostic methods, and management strategies for equine strangles based on UC Davis Center for Equine Health guidelines.

Strangles

A highly contagious equine upper respiratory tract disease caused by the bacterium Streptococcus equi subspecies equi, characterized by swollen lymph nodes and abscess formation.

Streptococcus equi subspecies equi (S. equi)

The bacterium that causes strangles by crossing nasal and oral mucous membranes to infect lymph nodes, leading to swelling and abscess formation.

Metastatic Strangles

Also known as 'bastard strangles,' a complication of strangles in which S. equi abscesses form in other lymph nodes throughout the body, such as in the brain, abdomen, or mammary gland.

Asymptomatic Carrier (Strangles)

A horse that appears healthy but harbors S. equi bacteria in its guttural pouches, intermittently shedding the organism and serving as a chronic reservoir for infection.

Incubation Period (Strangles)

The period of $3\text{ to }8$ days following infection, after which clinical signs such as fever, lethargy, anorexia, nasal discharge, and lymph node swelling begin to appear.

Fever Onset (Strangles)

An abrupt fever exceeding $103^\bullet\text{F}$, which usually serves as the first clinical sign of strangles, occurring $2\text{ to }3$ days post-infection.

Microbial Culture (S. equi)

A widely available and low-cost diagnostic test taking $1\text{ to }2$ days that identifies live S. equi bacteria from upper respiratory samples, though it has limited sensitivity in early infection phases.

Quantitative Polymerase Chain Reaction (qPCR)

A fast, highly sensitive diagnostic test that detects S. equi DNA on the same day, though it cannot differentiate between live and dead bacteria.

Tracheostomy

A surgical opening created through the neck into the windpipe, performed in severe strangles cases to relieve upper respiratory obstruction.

Antibiotic Controversy in Strangles

The debate surrounding antibiotic use (such as penicillin, ceftiofur, or ampicillin), which can prevent abscess formation but may alter the post-infection immune response and leave horses at risk for re-infection.

Isolation Temperature Threshold

A monitoring threshold where horses exhibiting a temperature over $101.5^\bullet\text{F}$ must be isolated immediately to prevent potential bacterial transmission.

Nasal Shedding Duration

The duration of S. equi bacterial release from the nasal tract, which can persist for up to $3\text{ weeks}$ and render horses infectious for at least $6\text{ weeks}$ after nasal discharge stops.

Pasture Rest Period

A biosecurity measure requiring pastures and stables that housed infected horses to be kept empty for $4\text{ to }6\text{ weeks}$ to minimize exposure risks.