Changes in Patterns of Disease in Dolphins Stranding Along the Texas Gulf Coast
Department of Pathology, The University of Texas Medical Branch; The Department of Marine Biology, Texas A&M University at Galveston, and the Texas Marine Mammal Stranding Network, Galveston TX, USA
During the years 1991-2003, 104 preservation code 2 dolphins and small whales stranding on the Gulf of Mexico coast of Texas were examined by necropsy. Eleven species were represented, including 85 Tursiops truncatus, the Atlantic bottlenose dolphin, 6 Peponocephala electra, 3 Stenella longirostris, 2 S. attenuata, 1 S. coeruloealba, 3 Kogia breviceps, 1 K. simus, and one each Globicephala macrorhynchus, Lagenodelphis hosei, Steno bredanensis, and Mesoplodon europaeus.
Changes in patterns of disease in the bottlenose dolphins were observed over that time. A new disease, "angiomatosis", was first recognized in 1991, in a mild form. By 1999, this disease had increased in incidence and severity to involve 100% of non-infant animals. In the past 3 years, incidence has remained high, but there appears to have been a significant drop in severity. Only T. truncatus has had this disease.
Over the same period of years, an occasional case of non-suppurative meningitis, often accompanied by hydrocephalus was recognized in T. truncatus, with as many as two occurring in the same year (1993 and 1999) for an incidence of six cases over the 9 year period. Six more cases have been recognized in 2000-2003, bringing the total incidence over the 13 years to 12 in 85 animals (14%), but 6 of 17 animals in the past 4 years (35%). The earlier cases were scattered in time and stranding location. The current group of cases range throughout the entire TMMSN stranding area, from Sabine Pass to Padre Island, and involve both old and young animals. This disease complex has been found in four animals who were alive when stranded, and who were observed for relatively short periods of rehabilitation. Three showed severe impairment of neurological function. The fourth seemed well for 3 months, then abruptly deteriorated and died, with hydrocephalus.
The histopathology is consistent with a non-suppurative, chronic inflammation, with hydrocephalus resulting from fibrotic occlusion of the exit foramina from the ventricles. Vasculitis of the cervical rete is also a frequent component.
Only in the last case has an agent been identified despite specific search. In that case, which appears to be in an earlier stage of evolution, a marine Brucella was isolated. While it is not surprising that meningitis and its complications can occur in dolphins, and indeed, meningitis associated with Brucella has been reported, we are not aware of previous reports of acquired hydrocephalus in any Cetacean. 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.
It is of interest to note that we have not seen meningitis in any species other than T. truncatus, and that while cerebral parasitism (Nasitrema sp.) is common in non-Tursiops dolphins in our region, we have never observed an instance in Tursiops.