Actinobacillus lignieresii infection in two horses.

This research study investigates Actinobacillus lignieresii infections in two different horses presenting with swellings. Through biopsies, culture testing, and prolonged treatments, the swelling was decreased without upsetting the pregnancy, marking the first reported cases of mastitis and chronic nasal cellulitis caused by this type of infection in horses.

Research Motivation and Background

The authors were motivated by clinical cases of swelling in horses, one related to a pregnant Norwegian Fjord horse, and another in a young American Paint filly. Understanding the cause of these swellings and finding an effective treatment was crucial, particularly as a pregnant horse was involved.

Research Methodology

• Both horses were presented for examination due to visible swellings, the examination included biopsy specimen analysis.
• The biopsies revealed the presence of diffuse dermal fibrosis, micropustule formation, and vascular thrombosis.
• The team isolated large numbers of Actinobacillus lignieresii, suggesting a bacterial infection was the cause.
• The treatment protocol involved intravenous administration of sodium iodide and oral administration of trimethoprim-sulfamethoxazole for the pregnant horse.
• The young filly was treated with oral administration of rifampin and trimethoprim-sulfamethoxazole.

Key Findings

• The swelling reduced in the Norwegian horse due to treatment without inducing abortion, indicating that the therapy was safe for pregnant horses.
• In the American Paint filly, the treatment resulted in complete resolution of clinical signs implying it was effective against the infection.
• This research marks the first known report of mastitis (inflammation of the mammary gland) and chronic nasal cellulitis (a skin condition resulting from a bacterial infection) caused by Actinobacillus lignieresii infection in horses.

Implications and Importance of Research

• This research provides valuable insights into understanding Actinobacillus lignieresii infections in horses, a topic not heavily covered in existing veterinary literature.
• The study provides evidence on effective treatment protocols that can be used safely in pregnant horses.
• By understanding the role of Actinobacillus lignieresii in certain horse conditions, more accurate diagnosis and effective treatments can be established in the veterinary field.