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Peer-reviewed veterinary case report

Actinobacillus lignieresii infection in two horses.

Journal:
Journal of the American Veterinary Medical Association
Year:
1999
Authors:
Carmalt, J L et al.
Affiliation:
Department of Veterinary Internal Medicine · Canada
Species:
horse

Plain-English summary

Two horses were diagnosed with infections caused by a bacteria called Actinobacillus lignieresii. The first horse was a 10-year-old pregnant Norwegian Fjord with a swollen muzzle that had been present for two years. After testing, it was found that the bacteria were causing the issue, and treatment with sodium iodide and a combination antibiotic helped reduce the swelling without causing any problems with the pregnancy. The second horse was a 5-month-old American Paint filly with swelling in her udder, and after treatment with different antibiotics, her symptoms completely went away. This study highlights a new understanding of how this bacteria can cause infections in horses.

Abstract

A 10-year-old pregnant Norwegian Fjord horse was examined for gross swelling of the muzzle of 2 years' duration. Examination of biopsy specimens revealed diffuse dermal fibrosis, micropustule formation, and vascular thrombosis; large numbers of Actinobacillus lignieresii were isolated in pure culture. Prolonged treatment with i.v. administration of sodium iodide and oral administration of trimethoprim-sulfamethoxazole caused regression of the swelling and did not induce abortion. A 5-month-old American Paint filly was examined for swelling in the udder region. Bacteriologic culture of purulent material obtained from the left teat revealed A lignieresii. Treatment with oral administration of rifampin and trimethoprim-sulfamethoxazole resulted in complete resolution of clinical signs. To the authors' knowledge, these findings represent the first report of mastitis and chronic nasal cellulitis caused by A lignieresii infection in horses.

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Original publication: https://pubmed.ncbi.nlm.nih.gov/10496138/