Listeria monocytogenes septicaemia in 2 neonatal foals

Listeria monocytogenes associated kerato-conjunctivitis in four horses in Norway

Listeria monocytogenes has been reported to cause various infectious diseases in both humans and animals. More rarely, ocular infections have been reported. To our knowledge, only two cases of Listeria keratitis have been described in horses. We report kerato-conjunctivitis in four Norwegian horses associated with L. monocytogenes. Clinically, all cases were presented with recurrent unilateral kerato-conjunctivitis. L. monocytogenes bacteria were isolated from swab samples from all cases, and cytology carried out in 3 cases was indicative of L. monocytogenes infection. The present report describes the first known cases in which L. monocytogenes has been isolated from keratitic lesions in horses in Norway. A potential risk factor may be feeding of silage or haylage, but other sources of infection cannot be ruled out. The phenotypic features including antimicrobial susceptibility and serotype of the isolates are described. Laboratory detection of L. monocytogenes demands extra caution since only low numbers of bacteria were detected in the eye-swabs, probably due to the low volume of sample material and the intracellular niche of the bacterium. A general poor response to treatment in all these cases indicates that clinicians should pay extra attention to intensity and duration of treatment if L. monocytogenes is identified in connection with equine kerato-conjunctivitis.

Clinical, pathological, and genetic characterization of Listeria monocytogenes causing sepsis and necrotizing typhlocolitis and hepatitis in a foal

Listeria monocytogenes was isolated from the blood, lungs, and liver of a 5-week-old American Quarter Horse filly that presented with a 2-day history of fever, lethargy, ataxia, and seizure activity. The foal was born on a well-managed breeding facility to a multiparous mare with no periparturient complications. At 8 hr of age, the foal had an adequate passive transfer of immunity (immunoglobulin G > 2,000 mg/dl). Since the time of birth, the foal reportedly had mild, intermittent diarrhea that responded to gastrointestinal protectants and probiotics. Despite prompt and aggressive treatment after hospital referral, the foal's condition deteriorated, and the foal was humanely euthanized. Postmortem gross and histopathologic examination revealed severe hepatitis with necrosis and fibrinonecrotic typhlitis and colitis. In addition to a positive blood culture for L. monocytogenes, immunohistochemistry confirmed the presence of this bacterium in the liver, cecum, and colon. Furthermore, a multiplex polymerase chain reaction identified the etiologic organism as a virulent L. monocytogenes strain.