High severity

Pigeon fever (Dryland distemper)

Pigeon fever is an infection with Corynebacterium pseudotuberculosis that often forms deep abscesses in the chest and pectoral muscles (dryland distemper) — it can also show as ulcerative lymphangitis or internal abscesses. It is not strangles (Streptococcus equi — lymph nodes / respiratory), not cellulitis (a sudden hot painful limb swell), and not an ordinary chest bruise. A photograph cannot diagnose pigeon fever. A still cannot tell pigeon fever from cellulitis, strangles, an ordinary chest abscess, or insect-bite/trauma swelling. Diagnosis is a vet exam. The skin scan is a first look at the chest skin/swelling to share with a vet, not a pigeon-fever test, and there is no pigeon-fever scanner.

Symptoms to watch for

Swelling, heat, or a mass on the chest or pectoral muscles — the swell is a clue, not a still-photo verdict

Draining tracts or thick discharge from a chest or pectoral swell

A chest or limb swell that can look like cellulitis, strangles, an ordinary abscess, or insect-bite/trauma swelling — a still cannot tell them apart

Fever, dullness, or reluctance to move — a reason to book a vet, not a photo verdict

Hind-limb swelling or oozing sores that can look like cellulitis (ulcerative lymphangitis form) — location is a clue, not a diagnosis

Some horses show only a chest swell at first; draining tracts or fever can come later — that is a vet visit, not a photograph

Common causes

Infection with Corynebacterium pseudotuberculosis, often deep in the pectoral muscles (dryland distemper), which can drain through tracts
Flies, contaminated soil, or a wound can carry the bacteria — the history is a clue, not a diagnosis
Not strangles (Streptococcus equi — lymph nodes / respiratory), not cellulitis (a sudden hot painful limb swell), and not an ordinary chest bruise
Not an ordinary chest abscess and not insect-bite/trauma swelling — a still cannot tell pigeon fever from those, and those need a vet

Prevention

Watch the chest, pectorals, and limbs for new swelling, heat, pain, or a draining tract and isolate rather than waiting on a photo
Reduce fly exposure and keep wounds clean — flies and soil are a common history, not a photo verdict
Do not share tack, needles, or wash gear with a horse that has a draining swell
Do not treat a photo, a chest swell, or a scan result as a diagnosis
Skin photos can help you and the vet look at the chest skin and swelling — they do not confirm or rule out pigeon fever, and they cannot tell it from cellulitis, strangles, an ordinary abscess, or insect-bite/trauma swelling

What to do

1
Book a vet visit if the chest, pectorals, or a limb is swollen, hot, painful, or draining. Diagnosis is a vet exam — not a photograph.
2
Isolate the horse from herdmates and keep flies off a draining swell. Do not lance, squeeze, or poultice a deep swell from a photo.
3
Photograph the swell in good light, from the front and from the side, and keep the photos on the horse's record so you and the vet can see change over time — a first look to share, not a diagnosis.
4
Use a skin scan only as a first look at the chest skin/swelling to share, not as a pigeon-fever test. There is no pigeon-fever scanner.
5
If pigeon fever (Corynebacterium pseudotuberculosis / dryland distemper) is confirmed, follow the plan your vet prescribes. Do not start a treatment protocol from a photo.
6
Keep the vet on the same page. Share what you see; do not treat a photo as a verdict.

When to call the vet

Pick up the phone if…

Schedule a vet visit if the chest, pectorals, or a limb is swollen, hot, painful, or draining, or if the horse is dull or off feed. Call sooner if there are multiple swellings, lameness, respiratory signs, or you are worried about spread to other horses — that is a vet call (contagious), not a photo diagnosis. A photograph cannot diagnose pigeon fever. A still cannot tell pigeon fever from cellulitis, strangles, an ordinary chest abscess, or insect-bite/trauma swelling. Diagnosis is a vet exam. The skin scan is a first look at the chest skin/swelling, not a pigeon-fever test, and there is no pigeon-fever scanner.

Get a first look at the chest skin

Scan the skin in HorseCare. 5 free scans this month, then Pro.

Scan the skin

5 free scans this month, then Pro. Scans run in the HorseCare app.

Educational content only. Not a substitute for veterinary advice.