Diagnosis of Parelaphostrongylus spp. infection as a cause of meningomyelitis in calves.

Migration of Parelaphostrongylus spp. has been documented to cause central nervous system damage in a number of aberrant host species but appears to be uncommon in cattle. The current report describes the clinical and laboratory findings, antemortem and definitive diagnosis, and response to treatment of Parelaphostrongylus spp. infection in five 3-7- month-old Limousin calves from 2 farms. All calves had signs of acute (n = 2) and chronic (n = 3) progressive spinal cord dysfunction. Cerebrospinal fluid analysis revealed a marked eosinophilic (acute cases) or lymphocytic (chronic cases) pleocytosis and elevated protein in all calves. A necropsy and histopathologic evaluation was performed on 2 euthanized calves, and histopathology revealed lymphoplasmacytic and eosinophilic meningomyelitis with multiple intradural and intramedullary expansile hyperplastic lymphoid nodules containing germinal centers and nematode fragments. DNA sequencing was performed on nested polymerase chain reaction products amplified with parasite-specific primers obtained from formalin-fixed and frozen spinal cord; PCR products from these 2 calves were 100% identical to Parelaphostrongylus species on DNA sequencing, confirming the diagnosis. Surviving calves rapidly improved following treatment with anthelmintics and corticosteroids. This case series identified Parelaphostrongylus spp. (likely P. tenuis) as a cause of spinal cord disease in calves and highlights the need for vigilance against aberrant parasite migration in calves grazing wet, snail-infested pastures. Cerebrospinal fluid eosinophilia is useful for supporting an antemortem diagnosis of Parelaphostrongylus in calves with acute neurologic disease; however, a lymphocytosis is observed in chronic or treated cases.