Neosporosis in 21 adult dogs, 2010-2023.

Background: Limited information is available regarding the clinical features, treatment, and prognosis of neosporosis in adult dogs.

Objective: Describe the clinical signs, laboratory findings, magnetic resonance imaging (MRI) findings, treatment and outcome in adult dogs (>6 months) diagnosed with neosporosis based on consistent clinical signs and positive serology (titer ≥1 : 800) at a referral hospital in Sydney, Australia.

Animals: Twenty-one client-owned dogs.

Methods: Retrospective case series of affected dogs between 2010 and 2023. Survival times were determined from onset of clinical signs to date of death or censoring.

Results: Clinical signs varied, and were indicative of generalized myopathy (6 dogs), multifocal intracranial disease (7 dogs), myelopathy (4 dogs), polyneuropathy (2 dogs) and single cases of focal myopathy and cerebellar disease. Serum creatine kinase activity was markedly increased (median, 3369 U/L) in most dogs. The most common MRI abnormalities were multifocal intracranial abnormalities (7/13 dogs) and muscle changes (5/13 dogs) whereas T2-weighted cerebellar abnormalities (2/13 dogs) and cerebellar atrophy (1/13) were less common. Treatment response was complete (resolution to normal) in 8 dogs, incomplete (persistent neurological deficits) in 6 dogs, but there was minimal response in 7 dogs. Thirteen dogs (62%) were alive after 6 months and 12 dogs (57%) alive after 1 year. Relapse was common, with 4 dogs experiencing at least 1 relapse event during the follow-up period.

Conclusion and clinical importance: Adult-onset neosporosis is uncommon and has variable clinical presentations. Treatment response also is variable, and relapse can occur, even among patients that respond completely to initial treatment.