Recumbent, 4 yo QH gelding. Owner reports standing quietly 12 hrs ago and progressed to stiff gait and then unwillingness to rise. Other horses in barn showing mandibular lymphadenopathy. What is primary differential?

Recumbent, 4 yo QH gelding. Owner reports standing quietly 12 hrs ago and progressed to stiff gait and then unwillingness to rise. Other horses in barn showing mandibular lymphadenopathy. What is primary differential?

• A. Equine influenza
• B. Staphylococcus aureus
• C. Streptococcus equi
• D. EHV-1

Answer: (C)

The scenario is best explained by Streptococcus equi infection causing strangles. The key clue is the recumbent, progressively stiff horse paired with swelling of the mandibular (submandibular) lymph nodes in other horses. Strangles is a highly contagious upper-respiratory infection in young horses that classically causes painful inflammation and abscessation of the submandibular lymph nodes, which can lead to reluctance to eat, drink, or stand, and in severe cases to systemic illness or recumbency if an abscess ruptures or toxemia develops. The herd pattern of mandibular lymphadenopathy strongly supports this diagnosis. Equine influenza would more likely present with fever, cough, nasal discharge, and overall malaise, without the characteristic unilateral or bilateral mandibular lymph node swelling seen with strangles. EHV-1 can cause respiratory signs or neurologic disease, including ataxia and recumbency, but mandibular lymphadenopathy is not a defining feature, and neurologic signs would typically be prominent if the myeloencephalopathy form were involved. Staphylococcus aureus infections can cause abscesses, but their presentation is usually localized and not the herd-wide submandibular lymph node involvement seen here. So, the primary differential is infection with Streptococcus equi causing strangles, given the clinical picture and the herd pattern of mandibular lymphadenopathy.

The scenario is best explained by Streptococcus equi infection causing strangles. The key clue is the recumbent, progressively stiff horse paired with swelling of the mandibular (submandibular) lymph nodes in other horses. Strangles is a highly contagious upper-respiratory infection in young horses that classically causes painful inflammation and abscessation of the submandibular lymph nodes, which can lead to reluctance to eat, drink, or stand, and in severe cases to systemic illness or recumbency if an abscess ruptures or toxemia develops. The herd pattern of mandibular lymphadenopathy strongly supports this diagnosis.

Equine influenza would more likely present with fever, cough, nasal discharge, and overall malaise, without the characteristic unilateral or bilateral mandibular lymph node swelling seen with strangles. EHV-1 can cause respiratory signs or neurologic disease, including ataxia and recumbency, but mandibular lymphadenopathy is not a defining feature, and neurologic signs would typically be prominent if the myeloencephalopathy form were involved. Staphylococcus aureus infections can cause abscesses, but their presentation is usually localized and not the herd-wide submandibular lymph node involvement seen here.

So, the primary differential is infection with Streptococcus equi causing strangles, given the clinical picture and the herd pattern of mandibular lymphadenopathy.