Bloody diarrhoea in dogs: AHDS and urgent treatment

Overview

AHDS is a syndrome in which bloody diarrhoea starts suddenly. It was previously called haemorrhagic gastroenteritis, or HGE. The name changed because the stomach generally lacks the mucosal damage found in the intestine. The illness can appear completely unexpectedly in a previously healthy dog.

Faeces may resemble red berry jam. Appearance alone does not establish the diagnosis. There is no single specific test confirming AHDS. Diagnosis relies on signs, blood concentration and exclusion of other diseases. One report from northern Europe described individual cases occurring fairly regularly throughout the year.

Causes

The exact mechanism of AHDS remains unclear. Clostridium perfringens and particularly its netF toxins, or bacterial poisons, have been associated with the disease. These bacteria can also occur in healthy dogs' intestines. Finding the bacterium therefore does not automatically explain every sign.

Increased intestinal lining permeability allows fluid to leak into the gut. Blood proteins can move into the intestine too. Red blood cells also leak into it. Tissue findings include death and inflammation of the intestinal lining. The most severe changes are often in the large intestine.

Bacterial toxins can damage the intestinal lining and underlying blood vessels. It is not entirely clear whether bacterial overgrowth initiates disease or follows other intestinal damage. Profuse bloody diarrhoea can also result from parvovirus, parasites or a clotting disorder, for example.

Risk factors

AHDS is more common in small and toy-breed dogs. Overrepresented breeds include Yorkshire Terriers, Miniature Pinschers, Miniature Schnauzers, Miniature Poodles and Maltese. A median age of 5 years has been described in affected dogs. The median describes the middle of the age distribution, rather than a lower or upper age limit.

However, the syndrome can affect any breed, size or age. Sex does not restrict the disease to particular dogs either. You may recall no unusual eating or other triggering event. An ordinary daily routine therefore does not rule out AHDS.

Typical symptoms

Signs usually begin quickly and can progress over a short period. Vomiting may start before visible bloody diarrhoea. Signs you may notice at home include:

• Sudden, profuse, reddish or clearly bloody diarrhoea.
• Vomiting accompanying or preceding diarrhoea.
• Markedly reduced appetite.
• Abdominal pain and tenderness.
• Unusual tiredness or weakness.
• Fever in some affected dogs.

Vomit may also contain blood. Heart rate may increase too. Severity does not depend on faecal colour alone. Vomiting accelerates dehydration alongside diarrhoea. Inadequate circulation can develop before dehydration is clearly recognisable.

Complications and consequences

The most serious early danger is hypovolaemic shock, circulatory failure caused by too little circulating blood volume. Major protein losses can substantially lower blood protein levels. Sepsis, a severe systemic infection, can also develop. Severe disease may involve DIC, a widespread blood-clotting disorder.

Fluid loss can disturb electrolyte balance. It can also strain the kidneys. Without treatment, severe illness can cause organ damage and death. With appropriate care, the outlook for AHDS is usually good. Mortality in hospitalised dogs is below 10%. This figure does not describe risk in dogs left untreated at home.

Diagnosis at the vet

The vet first assesses circulation, fluid loss and general condition. A key blood measurement is haematocrit, the proportion of blood volume occupied by red blood cells. In AHDS, it is often above 60%. A dog's usual haematocrit is about 37–55%. An increase reflects blood becoming concentrated as fluid is lost.

High haematocrit together with normal or slightly reduced total blood protein is a clue to AHDS. Anaemia, or too few red blood cells, is not a typical initial finding despite bloody faeces. The blood count may also show increased neutrophils, a type of white blood cell. If their number is low instead, sepsis or parvovirus must be considered.

Blood biochemistry looks for abnormalities including low blood glucose. Potassium, sodium and chloride can also fall with intestinal losses. Markedly abnormal clotting tests may require investigation of another clotting disorder or DIC. Urine testing may be included.

Faecal samples can be checked for intestinal parasites. Parvovirus is important to exclude as a cause of similar signs. X-rays are needed if a foreign body or intestinal blockage is suspected. Abdominal ultrasound adds to the investigation when necessary. Imaging in AHDS may show fluid-filled bowel loops and loss of intestinal motility.

Other causes to investigate include pancreatitis and adrenal insufficiency, or Addison's disease. Bloody diarrhoea can also involve rat poison or a platelet disorder. Severe intestinal ulceration, a tumour or intestinal perforation are other possible diagnoses. Black, tarry faeces, called melaena, contain partly digested blood. The source may be higher in the digestive tract or even in the mouth or airways.

Measurements of blood acidity and bicarbonate can support other investigations. In this context, marked neutrophilia means more than 25 billion cells per litre of blood. The white blood cell abnormality then particularly affects assessment of systemic infection and antimicrobial needs.

Some cases may also require gastrointestinal endoscopy performed by the vet.

Treatment

The vet prescribes treatment and medicines. Promptly started intravenous fluids are central to AHDS care. Fluid therapy is tailored to circulation, degree of dehydration and ongoing losses. Fluids given under the skin are generally insufficient for a severely ill dog's major losses.

Potassium deficiency is corrected when needed according to blood results. Low blood glucose may require glucose added to fluid therapy. Plasma or another colloid fluid may be used for severe protein deficiency or shock. Anti-sickness medicine can control vomiting. Pain relief may also form part of treatment.

Antibiotics are not automatically recommended for mild or moderate AHDS. This also applies to bloody diarrhoea when general condition is good and there is no dehydration or systemic illness. Moderate cases improving with fluids can also be treated without antibiotics.

Antibiotics are considered particularly when severe systemic signs persist despite adequate fluids. Marked white blood cell abnormalities may also change the decision. In severe disease, antimicrobials are usually injected into a vein or muscle. Choice depends on local resistance patterns and previous antibiotic treatment as well as the patient's condition.

Probiotics are sometimes used as supportive care, but no recommendation is made for or against routine use. They do not replace fluids for a severely ill dog. Once eating is possible, easily digested food is offered in small portions. Early feeding supports intestinal care when the vet considers it appropriate. The recovery diet may also be low-fat.

Many dogs begin improving within the first 24 hours in hospital. Discharge is often possible within 3 days. Severe AHDS is assessed daily during hospital treatment. After discharge, continue medicines and feeding according to individual instructions. Do not improvise prolonged fasting or start human diarrhoea medicines yourself.

In AHDS dogs without signs of sepsis, antibiotics did not reduce mortality. They did not shorten hospital stays either. Sign severity also did not change with antibiotics. This supports choosing medication according to disease severity rather than the sight of blood alone.

A dog recovering from vomiting may have food divided into 3–6 small meals daily, for example, according to the veterinary plan. Easily digested food aids nutrient absorption in the damaged intestine. However, a simple homemade chicken-and-rice diet is not nutritionally balanced for long-term feeding.

Prevention

There is no known reliable prevention for AHDS because its exact mechanism is unclear. A previously healthy dog fed normally can also become ill unexpectedly. To prevent other diarrhoea causes, avoid sudden diet changes. A food transition can be extended from a week to 2 weeks when needed. If your dog has a known food allergy or sensitivity, avoid the ingredient causing signs. These measures address other causes of digestive upset rather than proven AHDS prevention.

Important for dog owners

Photograph the faeces and bring a sample to the appointment if possible. A sample helps the vet assess appearance and the investigations needed. Record when signs began, vomiting episodes and whether your dog has drunk or eaten. Report all current medicines and possible access to medicines, poisons or foreign bodies. Mention vaccinations and signs in other household animals too.

Keep fresh water available. Do not prolong home care of bloody diarrhoea if your dog is weak or signs are severe. AHDS can rapidly lead to shock. Do not give human diarrhoea medicines yourself, as some can harm dogs. At discharge, agree follow-up and which signs mean you should return for treatment immediately.

Frequently asked questions

Is bloody diarrhoea always AHDS?

No. Similar signs can result from parvovirus, intestinal parasites and clotting disorders, among other causes. A foreign body must also be excluded when necessary. Faecal appearance provides useful information, but examination and blood tests are often needed.

Can AHDS spread to another dog?

AHDS is not considered contagious between dogs. However, bloody diarrhoea can also have a contagious cause such as parvovirus. Faeces alone therefore cannot establish the risk to other dogs. Follow veterinary instructions on contact and cleaning until the cause has been investigated.

Why is my dog not given antibiotics immediately?

Routine antibiotics are not recommended for mild or moderate AHDS. The most important treatment is prompt fluid therapy. Medication may nevertheless be needed with suspected sepsis or other severe illness that does not improve with fluids.

How quickly should my dog recover?

Many dogs improve within 24 hours of starting hospital treatment. They often go home within 3 days. These are typical treatment courses, rather than deadlines for waiting at home. Contact the vet treating your dog if their condition worsens or signs return after discharge.

Why is haematocrit high when there is blood in the faeces?

In AHDS, fluid leaks into the intestine and blood becomes concentrated. The red blood cell volume fraction can therefore exceed 60%. At the same time, total blood protein may remain normal or fall. Bloody faeces therefore do not mean the first blood test must always show anaemia.