Hemorrhagic gastroenteritis (now called Acute Hemorrhagic Diarrhea Syndrome or AHDS) causes sudden, severe bloody diarrhea and can kill a small dog through dehydration within hours. Most dogs recover fully with rapid veterinary treatment, but delay worsens outcomes significantly. Any dog passing bloody diarrhea should be seen the same day.
Last reviewed: June 2026
What Is Dog Hemorrhagic Gastroenteritis (AHDS)?
Acute Hemorrhagic Diarrhea Syndrome (AHDS) — formerly called hemorrhagic gastroenteritis or HGE — is a sudden-onset gastrointestinal condition characterized by profuse, bright red or "raspberry jam" bloody diarrhea, often accompanied by vomiting. The underlying cause is not fully understood, but Clostridium perfringens overgrowth and associated toxins in the intestinal lumen are strongly implicated, as described in Ettinger's Textbook of Veterinary Internal Medicine. The disease is not contagious, does not require a dietary indiscretion trigger, and can occur in otherwise completely healthy dogs without warning.
AHDS is especially dangerous because it causes massive fluid shifts out of the bloodstream into the gut, producing hypovolemic shock quickly — particularly in small breed dogs under 10 kg. Hematocrit (packed cell volume) classically spikes above 60% as the blood thickens from fluid loss. The AAHA Canine Life Stage Guidelines, 2019 highlight that prompt hospitalization and IV fluid resuscitation are the cornerstone of treatment for acute gastrointestinal emergencies in dogs.
Signs to Watch For
AHDS typically strikes healthy dogs without warning. The hallmark is large-volume, bright bloody diarrhea — often resembling red raspberry jam — combined with one or more of the following:
- Sudden vomiting, which may also contain blood
- Extreme lethargy and weakness
- Loss of appetite
- Abdominal pain (hunching, reluctance to move)
- Rapid progression from mildly unwell to severely ill within hours
The condition can progress from first diarrhea to hypovolemic shock in as little as 4–8 hours in small dogs, as described in Nelson & Couto's Small Animal Internal Medicine.
Diagnosis and Treatment
Diagnosis is based on clinical presentation, physical exam findings (tacky mucous membranes, elevated heart rate, very high PCV), and ruling out other causes of bloody diarrhea (parvovirus, foreign body, intussusception, toxin ingestion). Blood work, fecal parvovirus PCR, and abdominal x-rays or ultrasound are standard.
Treatment centers on aggressive IV fluid resuscitation to restore circulating volume and correct the hemoconcentration. Most dogs respond dramatically within 12–24 hours of IV fluids. Antibiotics are used selectively when bacterial involvement is suspected. Anti-nausea medications (maropitant, ondansetron) control vomiting. Nutritional support begins early — small amounts of a bland, easily digestible food are often introduced within 12–24 hours. Most dogs are discharged within 1–3 days and recover fully.
When to See a Vet
Call your vet today if:
- Your dog passes diarrhea with any blood in it, even a small amount
- Your dog has vomited and also has diarrhea within the same 24-hour period
- Your dog seems unusually lethargic alongside GI signs
Go to the ER immediately if:
- Your dog is passing large volumes of bright red or bloody diarrhea
- Your dog seems weak, wobbly, or collapsed
- Gums are pale, white, or tacky and dry to the touch
- Symptoms are progressing rapidly over 1–2 hours
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Frequently Asked Questions
How do I tell AHDS from normal bloody diarrhea?
AHDS produces dramatically more blood than typical diarrhea with a streak of blood. The stool looks like raspberry jam or pure bright red blood. The dog is also typically more profoundly ill — significantly lethargic, vomiting, and deteriorating rapidly. Any bloody diarrhea warrants same-day veterinary assessment; the severity determines urgency.
What does dog hemorrhagic gastroenteritis treatment cost?
Hospitalization for AHDS typically runs $800–2,500 depending on severity and length of stay. A mild case requiring 12–24 hours of IV fluids may cost $500–900. Severe cases with 2–3 days of intensive care, multiple blood tests, and imaging can reach $2,000–3,500. Early treatment when the dog is not yet in shock is significantly cheaper.
Is AHDS contagious to other dogs?
AHDS itself is not contagious and does not spread between dogs. However, if the bloody diarrhea is caused by parvovirus (which looks similar), that is highly contagious. Your vet will test for parvovirus early to guide isolation decisions.
What causes AHDS in dogs?
The exact cause is not fully established, but Clostridium perfringens overgrowth and intestinal toxin production are strongly implicated. There is no identifiable dietary trigger in most cases — it can happen to any dog. Small breed dogs (Miniature Schnauzers, Dachshunds, Yorkshire Terriers, Maltese) appear to have higher incidence.
Can AHDS recur?
Some dogs experience recurrent episodes, but the majority have a single event and do not relapse. Dogs that have had one episode may benefit from having probiotic support and a consistently appropriate diet to maintain gut microbiome stability.
Still Not Sure if Your Dog Needs a Vet?
When you're not sure if this is wait-and-see or call-tonight, Voyage AI Vet triages in under 2 minutes. Describe what you're seeing in chat, share photos of the diarrhea if possible, note whether vomiting is occurring and how quickly symptoms developed, or hop on a live video call if you want a second pair of eyes. Every answer comes with citations to the actual veterinary literature it's pulling from — so you see exactly where the guidance comes from, not just a chatbot's word.