BREVETOXICOSIS IN MANATEES (TRICHECHUS-MANATUS-LATIROSTRIS) FROM THE 1996 EPIZOOTIC - GROSS, HISTOLOGIC, AND IMMUNOHISTOCHEMICAL FEATURES

In 1996, at least 149 manatees (Trichechus manatus latirostris) died i n an unprecedented epizootic along the southwest coast of Florida. At about the same time, a bloom of the brevetoxin-producing dinoflagellat es, Gymnodinium breve, was present in the same area. Grossly, severe n asopharyngeal, pulmonary, hepatic, renal, and cerebral congestion was present in all cases. Nasopharyngeal and pulmonary edema and hemorrhag e were also seen. Consistent microscopic lesions consisted of catarrha l rhinitis, pulmonary hemorrhage and edema, multiorgan hemosiderosis, and nonsuppurative leptomeningitis. Immunohistochemical staining using a polyclonal primary antibody to brevetoxin (GAB) showed intense posi tive staining of lymphocytes and macrophages in the lung, liver, and s econdary lymphoid tissues. Additionally, lymphocytes and macrophages a ssociated with the inflammatory lesions of the nasal mucosa and mening es were also positive for brevetoxin. These findings implicate breveto xicosis as a component of and the likely primary etiology for the epiz ootic. The data suggest that mortality resulting from brevetoxicosis m ay not necessarily be acute but may occur after chronic inhalation and /or ingestion. Immunohistochemical staining with interleukin-1-beta-co nverting enzyme showed positive staining with a cellular tropism simil ar to GAB. This suggests that brevetoxicosis may initiate apoptosis an d/or the release of inflammatory mediators that culminate in fatal tox ic shock.