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Archive Case #176: Equine Pigeon Fever

Horse veterinary case - Medium - August 26, 2026

Clinical Clues

  1. A horse develops a deep pectoral swelling and fever during a dry season with many biting insects.
  2. The swelling gradually becomes painful and fluctuant rather than resolving like simple bruising.
  3. The horse is dull, and a second smaller abscess is noted along the ventral midline.
  4. Ultrasound supports a well-formed abscess rather than diffuse cellulitis alone.
  5. Culture supports Corynebacterium pseudotuberculosis infection.
  6. Equine pigeon fever is the Corynebacterium pseudotuberculosis-associated syndrome known for pectoral abscesses and a pigeon-breasted appearance.

Diagnosis

Equine Pigeon Fever

This case is most consistent with Equine Pigeon Fever because the horse has a characteristic pectoral abscess with supportive culture for Corynebacterium pseudotuberculosis. The most important clues are the location and fluctuant abscess formation, which make a sterile hematoma less likely.

Learning review

Review the case evidence

Use the paired clues to explain how the evidence in this horse case supports the provided diagnosis, Equine Pigeon Fever, then compare your reasoning with the case explanation.

Evidence checkpoints

Clues 1-2

  1. Clue 1: A horse develops a deep pectoral swelling and fever during a dry season with many biting insects.
  2. Clue 2: The swelling gradually becomes painful and fluctuant rather than resolving like simple bruising.

Clues 3-4

  1. Clue 3: The horse is dull, and a second smaller abscess is noted along the ventral midline.
  2. Clue 4: Ultrasound supports a well-formed abscess rather than diffuse cellulitis alone.

Clues 5-6

  1. Clue 5: Culture supports Corynebacterium pseudotuberculosis infection.
  2. Clue 6: Equine pigeon fever is the Corynebacterium pseudotuberculosis-associated syndrome known for pectoral abscesses and a pigeon-breasted appearance.

Self-review prompts

  1. After clues 1-2, what evidence from this horse case shaped your initial interpretation?
  2. When you compare clues 3-4 with clues 1-2, what changed in your reasoning about Equine Pigeon Fever?
  3. How do clues 5-6 align with the case explanation for Equine Pigeon Fever?

Educational Use

Vetdle archive cases are educational veterinary games for diagnostic reasoning practice. They do not provide veterinary advice, diagnosis, treatment, or professional medical guidance.