During 1980, three cases of meningitis in lemon sharks were diagnosed by the Marine Pathology Laboratory. Two of these lemon sharks were exhibited at the Sealand Aquarium in Sandusky, Ohio, for four years. The other lemon shark was an exhibit at the Cleveland Aquarium for eight years. Sharks from both aquaria sporadically exhibited abnormal swimming and resting behavior for approximately 1 - 3 years. Reports of such behavior included loss of equilibrium, swimming upside down and lying upside down on the tank bottom.

Histopathological examination of meningeal tissues from these sharks indicated that the lesions were primarily vascular. The endothelial cells were swollen and disorganized. Vessel walls were necrotic and contained infiltrations of mononuclear cells. Trichrome stains of these sections indicated that collagen in the vessel walls was degenerating and being replaced by proliferating muscle tissue. Other lesions observed in meningeal and brain tissue were lymphocytic infiltrations, perivascular cuffing, and gliosis.

Such vascular lesions often occur in viral meningitis. However, inclusion bodies were not present. No virus-like particles were observed in meningeal sections under the electron microscope. Attempts to isolate a virus from meningeal and blood fractions were unsuccessful. Bacteria isolated from the meninges were identified as Citrobacter freundii, Corynebacterium pseudodintheriticum(?), and Micrococcus freundenreichii.