Mandibular lymphadenopathy caused by Actinomyces denticolens mimicking strangles in three horses

Identification of Actinomyces denticolens as a cause of a soft tissue abscess in a horse

“…They are most commonly known in veterinary medicine as the cause of ‘lumpy jaw’ in cattle ( A. bovis ) and have not been well recognised as a common cause of soft‐tissue abscesses in horses. However, A. denticolens has been identified in para‐oral infections in horses, and as a cause of submandibular and retropharyngeal lymphadenopathy and abscessation in a small number of horses in Switzerland, California, and Canada . It is possible that a much earlier report of an Actinomyces spp.…”

“…Soft‐tissue abscessation caused by A. denticolen s in horses most commonly involves the head region and includes presenting signs that are typical of strangles. In most of the reported cases, the horse has developed fever, anorexia, depression, painful swelling and abscessation of the submandibular lymph nodes followed by rupture and drainage of purulent material . In contrast with typical upper respiratory tract infection with S. equi subsp.…”

“…Fortunately, the management of superficial soft‐tissue abscesses caused by A. denticolens in any location is likely to follow the same basic principles as for the management of soft‐tissue abscesses caused by group C streptococci and other Gram‐positive bacterial species. The successful treatment in most cases has involved drainage and lavage of the abscess in combination with antimicrobial therapy including penicillin, doxycycline, trimethoprim–sulfonamide or a combination of these . In the reported cases, systemic antimicrobial therapy rather than drainage alone was often required and most of the horses responded rapidly to appropriate treatment with complete resolution of the abscess.…”

Actinomyces denticolenscolonisation identified in equine tonsillar crypts

“…In recent years, the rapid identification of Actinomyces species has become possible using the 16S rRNA gene sequence. Consequently, several researchers have identified the Actinomyces species isolated from the abscesses of the cervicofacial region in horses with similar clinical signs of strangles as Actinomyces denticolens ( Albini and others 2008 , Fielding and others 2008 , Beck and others 2011 , Feary and others 2013 ). The cause of these abscesses is speculated to be an intrinsic infection caused by A denticolens invading from the equine oral cavity ( Albini and others 2008 , Fielding and others 2008 , Beck and others 2011 ).…”

“…Consequently, several researchers have identified the Actinomyces species isolated from the abscesses of the cervicofacial region in horses with similar clinical signs of strangles as Actinomyces denticolens ( Albini and others 2008 , Fielding and others 2008 , Beck and others 2011 , Feary and others 2013 ). The cause of these abscesses is speculated to be an intrinsic infection caused by A denticolens invading from the equine oral cavity ( Albini and others 2008 , Fielding and others 2008 , Beck and others 2011 ). Due to the presence of Actinomyces species in the upper ( Bohra and others 2008 ) and lower respiratory tracts ( Bailey and Love 1991 ), it has not been sufficiently clarified whether or not A denticolens is a member of the usual microbiota in the oral cavity of horses.…”