Abstract

Three cases of chronic meningitis with hydrocephalus interna were identified among 61 (5%) bottlenose dolphins (Tursiops truncatus) stranding along the western (Texas) coast of the Gulf of Mexico in the years 1991-1998. A fourth animal had lymphocytic meningitis without hydrocephalus.

One animal with hydrocephalus was a 220 cm, 80.6 kg female, found dead in the Matagorda Island National Wildlife Refuge January 1, 1993. Age was determined to be 7 years by count of dentinal growth layer groups (GLG). Necropsy revealed hydrocephalus, with chronic lymphocytic meningitis, with fibrosis; emaciation, arthritis of the left flipper joint and arthritic fusion of the atlas with the skull. The brain weighed 1346 g.

The second animal was a 210 cm long, 96.8 kg male, which stranded alive on Galveston Island, June 7, 1995, badly shark-bitten. It survived for 3 days. Necropsy revealed hydrocephalus, with chronic lymphocytic meningitis, mainly basal; light lungworm infestation, and pancreatic duct flukes. The brain weighed 1245 g. Age was determined to be 3.5 years (GLG).

The third animal was found dead stranded on the beach at Sea Rim State Park, Jefferson County, Texas, December 8, 1998. Necropsy revealed pulmonary angiomatosis, marked myocardial contraction band necrosis, and hydrocephalus with chronic meningitis, among other, minor findings. The brain weighed 1338 grams.

In all of these animals the brains were within the weight ranges established as normal for body size in our stranded population of T. truncatus. All 3 cases were associated with non-suppurative lymphocytic meningitis, presumed to be of viral origin based on histological features, although a viral etiology was not specifically identified. None of the three had any morphologic evidence of morbillivirus infection in any tissue.

The fourth animal, without hydrocephalus, was a 216 cm long, 118 kg female, stranded at St. Luis Pass, Galveston Island, August 22, 1993. Tooth age was 9 years (GLG).

Findings included arthritis of several joints, including the atlanto-occipital, and abscesses in the subcutaneous tissue, muscle and kidney. The brain weighed 1404 g. Meningitis was present, but limited mainly to the spinal cord.

Hydrocephalus interna is a well recognized complication of chronic meningitis in humans, in which it is attributed to fibrotic occlusion of the foramina of Lushka and Magendie. Obstruction to flow of cerebrospinal fluid from the ventricular system through the foramina into the subarachnoid space with continued active secretion by the choroid plexus causes intraventricular pressure to rise, impeding circulation to the periventricular tissues, with subsequent atrophy.

While it is not surprising that meningitis and its complications can occur in dolphins, we are not aware of previous reports of acquired hydrocephalus in cetaceans. For lack of comparative data, we cannot determine whether the incidence of hydrocephalus reported is peculiar to bottlenose dolphins of the western Gulf of Mexico.