There are no reported cases of pulmonary amebiasis in dolphins. A critically ill dolphin showed signs of vertical posturing, anorexia, elevated enzyme activities, marked azotemia, hyperbilirubinemia, persistent tachycardia, and a marked degenerative left shift. Thoracic sonography revealed a substantial pleural effusion in the right hemi­thorax. Four liters of a sero sanguinous exudate was removed via pleurocentesis.

Cytological examination of Papanicolaou stained cyto spins of pleural fluid showed acute inflammation. Large numbers of amebas were interspersed with polymorphonuclear leukocytes, monocytes and lymphocytes. The amebas ranged in size from 6 to 14 microns with a mean of 8 microns and had pale granular cytoplasm. Although most of the amebas possessed a single 2-3 micron eccentric mono lobated nucleus with a large centrally placed, dense nucleolus, many binucleate and few with multiple nuclei were also present. The size of the amebas and especially the presence of bi- and trinucleate forms suggested that it is a vahlkampfiid (Naegleria type) ameba.

Diff-Quick stains showed the organisms to have pink cytoplasm and a slightly darker pink nucleus. Periodic acid-Schiff (PAS) and Gomori Methenamine Silver (GMS) stains failed to demonstrate the organism. Infrequently ameba showed phagocytosis of material, but there were no red blood cells present within the cytoplasm of the organism and the cytoplasm appeared different than the cytoplasm of degenerating polymorphonuclear leukocytes.

Electron microscopic ultrathin sections demonstrated organisms that ranged in size from 8 - 12 microns. The cytoplasmic membrane was trilaminar with multiple vesicles consistent with pinocytotic vesicles. The nucleus was sharply outlined and contained a dense nucleolus surrounded by a thin nuclear membrane. The majority of organisms were in varying degrees of disintegration. Numerous polymorphonuclear leukocytes were also present in the ultrathin section.

A piece of lung specimen with pleura, refrigerated for about two weeks, was processed for culture on two non-nutrient agar plates pre-coated with Escherichia cold bacteria, at the Division of Parasitic Diseases CDC, for isolation and identification of the organism. Of the two agar plates one was incubated at 24°C and the other at 37°C. No amebic growth was seen even after two weeks of incubation though few amebic cysts were seen at the site of inoculation of the sample.

Histologic sections of the lung revealed amebic enmeshed with the host cells in the pleura. Indirect immunofluorescence assay was also performed on the paraffin sections using antisera made in rabbits against: Acanthamoeba castellanii, Naegleria fowleri, N. gruberi, Vahlkampfia avara, Willaertia sp., Hartmannella vermiformis, Dictyostelium discoideum and Balamuthia mandrillaris. No fluorescence was seen indicating that the amebas in these sections were antigenically dissimilar to the amebas against which the antisera were made. Although free-living amebas belonging to the genera Naegleria, Acanthamoeba and Balamuthia have been known to cause a central nervous system disease in humans and other animals, we believe this is the first report of an infection of a dolphin caused by a small free-living ameba.