GASTROINTESTINAL TRACT BACTERIAL INFECTIONS IN HORSES

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Causative Agent(s)

Diarrhoea in adult horses could be acute or chronic. Bacteria, viruses, and toxins are all factors that could disrupt the integrity of the gastrointestinal tract mucosae resulting to diarrhoea and other complications. Bacterial organisms are the most common causes of infectious diarrhoea in horses, e.g., Salmonella serovars, Aeromonas spp., Clostridium difficile, and Clostridium perfringens.

Clinical Presentation and Epidemiology

Consistent clinical signs include diarrhoea, dehydration, anorexia, colic, and lethargy. Damage to the gastrointestinal mucosae often result in the translocation of bacterial organism(s) and/or their toxins into the systemic circulation and consequent septicaemic shock and death. However, confirmed bacterial infections of the GIT in adult horses are sporadic when compared with other companion animals like dogs and cats. Even when confirmed, they are self-limiting.

Management and Treatment

Since many cases of diarrhoea in adult horses are associated with transient digestive disturbances which are often self-limiting within a day or two, antibacterial treatment may not be obligatory. The mainstay of managing diarrhoea in horses include IV fluid therapy, electrolyte supplementation where necessary, and nutritional supports. But specific therapies include the use of antibacterial agents, anthelmintics, probiotics, binding agents, and gastro- protectants, etc. Antimicrobial therapy is often required in severely neutropaenic and/or immune-compromised horses with diarrhoea to protect against bacteraemia and/or toxaemia resulting from the translocation of primarily Gram-negative bacteria organisms and/or toxins (e.g., Clostridium spp.) via leaky tight junctions, particularly in colitis.

Intravenous gentamicin administration is an appropriate choice of antibacterial therapy because it has minimal effect on anaerobic bacterial organisms in the gastrointestinal tract, and thus has a low likelihood of inducing antimicrobial-associated diarrhoea. Nonetheless, it has been reported to up-regulate the production of β2 toxin by Clostridium perfringens and thus should be used only in clinical presentations whereby clostridiosis is ruled out. When Clostridium spp. are suspected or confirmed to be playing a pathogenic role in the disease, metronidazole should be the first drug of choice. In addition, flunixin meglumine, an analgesic, antipyretic, and anti-inflammatory drug could be included in the therapeutic regimen to attenuate endotoxaemia.

Gentamicin sulphate: 4-6mg/kg, slow IV for 6 hours. Metronidazole: 10-15mg/kg, q12h x 14 days, PO. Flunixin meglumine: 0.25mg/kg, q24h x 5 days, IM