Gill disease associated with Paramoeba pemaquidensis Page 1970 (Sarcomastigophora: Paramoebidae) infestations was observed in coho salmon Oncorhynchus lasutch reared in sea water Fish reared in net pens in Washington and in land-based tanks in California were affected. Approximately 25 O/ O mortality was observed in the net pens in 1985, and the disease recurred in 1986 and 1987. Amoeba infesting the gill surfaces elicited prominent epithelia1 hyperplasia. Typical of Paramoeba spp., the parasite had a Feulgen positive parasome (Nebenkorper) adjacent to the nucleus and floatlng and transitional forms had digitiform pseudopodia. We have established cultures of the organism from coho gills; it grows rapidly on Malt-yeast extract sea water medium supplemented with Klebsiella bacteria. Ultrastructural characteristics and nuclear, parasome and overall size of the organism in study indicated it is most closely related to the free-living paramoeba P. pemaquidensis. The plasmalemma of the amoeba from coho gills has surface filaments. Measurements (in pm) of the amoeba under various conditions are as follows: transitional forms directly from gills 28 (24 to 30), locomotive forms from liquid culture 21 X 17 (15 to 35 X 11 to 25), and locomotive forms from agar culture 25 X 20 (15 to 38 X 15 to 25). Nuclei and parasomes from liquid cultures were 5 to 7 and 3 to 5 X 2 to 3, respectively. The disease was not induced by laboratory exposure of coho salmon to amoeba cultures, but the amoeba was consistently isolated from exposed fish and aquarium detritus for 4 wk after exposure. This suggests that the organism is an opportunistic pathogen which only proliferates on fish gills and causes disease under certain situations yet to be clearly defined. In vitro studies indicated that the optimal salinity for growth of the amoeba was between 15 and 20 ppt, while growth was greatly dminished below 10 ppt. This concurs with field observations where the amoeba was eradicated from fish held in sea water tanks following a reduction in salinity.

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Amebae belonging to the order Leptomyxida are regarded as innocuous soil organisms incapable of infecting mammals. We report here the isolation of a leptomyxid ameba from the brain of a pregnant baboon (Papio sphinx) that died of meningoencephalitis at the San Diego Zoo Wild Animal Park. By using rabbit anti-leptomyxid serum in the immunofluorescence assay, we have identified the leptomyxid ameba in the brain sections of a number of human encephalitic cases from around the world as well as a few cases of meningoencephalitis in animals in the United States, which suggests that the leptomyxid amebae are potential etiologic agents of fatal meningoencephalitis in humans and animals.

Cell adhesion receptors, referred to as integrins, are recognized as key regulators of cellular processes including growth and differentiation. Integrins communicate with growth factor receptors (GFRs) to control specific cellular responses to stimuli originating in the extracellular environment. In this article, we review the role of integrins as molecular switches that modulate GFR activation and specificity. We also examine the reciprocal modulation of integrin functions by GFRs and the mechanisms through which those actions are fine-tuned.

A free-living amoeba identified as Hartmannella vermiformis was isolated from a water sample obtained during an investigation of nosocomial legionellosis. Hartmannella vermiformis is known to support the intracellular multiplication of Legionella pneumophila. This strain of H. vermiformis, designated CDC-19, was cloned and established in axenic culture to develop a model for the study of the pathogenicity of legionellae. Isoenzyme patterns of axenically-cultivated strain CDC-19 were compared with two strains of H. vermiformis derived from the type strain, one axenic (ATCC 50236) and the other grown in the presence of bacteria (ATCC 30966). Enzyme patterns suggested that all three strains are assignable to the species H. vermiformis. Axenic H. vermiformis strain CDC-19 has been deposited with the American Type Culture Collection (ATCC 50237) and should prove useful in the study of protozoan-bacterial interaction.