Antibiotic Responsive Diarrhoea

Signalment

• Common in young German Shepherd Dogs

Description

Antibiotic responsive diarrhoea (ARD) used to be termed small intestinal bacterial overgrowth (SIBO). It is a sign of an underlying disease rather than a diagnosis. The aetiology and pathogenesis of this disease is unknown. Few studies have documented the scale of increase in bacterial numbers or whether the growth is responsible for the clinical signs.

ARD can be classified as idiopathic or secondary. In cases of idiopathic ARD, the only consistent finding is response and remission with antimicrobial therapy. This has been found to be common, but not exclusively, in young German Shepherd Dogs. It has been suggested to be associated with IgA deficiency or dysregulation in this breed. However, the true underlying mechanism could be far more complex and numerous other hypotheses have been proposed. In contrast, there is usually an underlying intestinal disease in cases of secondary ARD. Diseases which can cause any of the following disorders of the intestines can result in secondary ARD:

• decrease gastric acid production
• increase small intestinal substrate
• partial obstruction
• anatomical disorders
• motility disorders

The consequences of ARD are:

• interference with fluid and nutritional absorption due to dysfunction of the enzymes located at the microvillous border.
• disturbance in mucosal permeability.
• deconjugation of bile acids.
• hydroxylation of fatty acids.

Diagnosis

Clinical Signs

• Chronic small intestinal diarrhoea
• Weight loss
• Failure to thrive
• Vomiting
• Variable appetite
• Borborygmi
• Abdominal discomfort

If no localising findings are obvious, a full investigation is recommended. This includes a full routine haematology, biochemistry, urinalysis, faecal bacteriology and parasitology, diagnostic imaging and gastroduodenoscopy. Trypsin-like immunoassay (TLI) can be used diagnose exocrine pancreatic insufficiency (EPI). These findings are usually unremarkable in cases of idiopathic ARD. In these instances, a trial treatment with antimicrobial therapy is warranted. If these animals are responsive to the antimicrobial, but the clinical signs relapse upon withdrawal of treatment, a true idiopathic ARD can then be made.

Currently, the gold standard direct test for diagnosing ARD is duodenal juice culture. Unfortunately, this is an expensive test and it is rarely available. Indirect tests such as serum folate and cobalamin concentrations have been used to analyse the bacterial concentrations in small intestines. Some species of bacteria may increase the level of serum folate concentration or decrease serum cobalamin concentration, or both. The sensitivity and specificity of this test is low and therefore their use in the diagnosis of ARD is questionable.

At present, there is not a single ideal or recommended diagnostic test for the diagnosis of idiopathic ARD. If secondary ARD is suspected, an investigation for the underlying cause is recommended.

Treatment

Idiopathic ARD

• Antimicrobial for an initial period of 4 weeks
  • A longer course may be required if the clinical signs relapse. This holds true for most cases of ARD.
  • Suitable drugs include oxytetracycline, tylosin, metronidazole. Oxytetracycline is the drug of first choice for idiopathic ARD but its use for secondary ARD is controversial. In addition, resistance is fast to develop with oxytetracycline. Tylosin and metronidazole may be more appropriate at targeting bacteria that are likely to be present in secondary ARD.

Secondary ARD

Treat the underlying cause of ARD

Dietary modification

A highly digestible and fat restriction diet, with added prebiotics is recommended. This may be useful in both idiopathic and secondary ARD.

Prognosis

For cases of secondary ARD, the prognosis depends on the underlying cause and success of treatment. For cases of idiopathic ARD, the prognosis is guarded and many of them are likely to relapse when treatment is stopped, which may require a prolonged or life-long treatment. Some cases, however, do resolve and only require a short term treatment.