Pyogranulomatous meningoencephalitis due to Actinomyces sp in a dog

Actinomyces sp. are commensal, filamentous, gram-positive, acid-fast-negati ve bacteria that can cause pyogranulomatous inflammation in animals and hum ans. Central nervous system (CNS) disease is a rare presentation of actinom ycosis and is usually due to extension from infected wounds or seeding from distant sites. A dog with progressive, poorly localized neurologic signs h ad primary CNS actinomycosis without history or evidence of previous trauma or other organ involvement. Histologically, there was a severe pyogranulom atous meningoencephalitis with intralesional filamentous bacteria that were also visible on cytology of the cerebral spinal fluid (CSF) postmortem. Ac tinomyces sp. was cultured postmortem from the CSF, confirming the diagnosi s. This case demonstrates that Actinomyces sp. can be a causative agent of primary CNS disease in dogs.