RESUMO
Rickettsial organisms are well-known fish pathogens in both natural and culture environments. This study reports an outbreak of disease in red tilapia larvae caused by piscirickettsia-like organisms (PLOs), which lasted from June until October 2009. Severe mortality was recorded almost exclusively in larvae and postlarvae aged 1-22 days old. Although clinical or gross findings were not evident in diseased fish, histopathology revealed severe necrosis of the epidermis and gill epithelium, with concomitant changes in the underlying skeletal muscle as being the most relevant microscopic lesions. Although PLOs were visible with the routine hematoxylin eosin technique, they were better observed with Giemsa and toluidine blue stains. Transmission electron microscopy revealed that the bacterium was located within the cytoplasm and phagolysosoma-like structures of epithelial cells from the gills and the skin. The bacteria measured 0.9 ± 0.2 µm × 2.1 ± 0.6 µm and had a double cell membrane (the outer one having undulating projections), with variable electron-dense and electron-lucent areas. Ultrastructurally, abundant myelin figures surrounded the microorganisms within host cell cytoplasm. Results indicated that Piscirickettsia-like organisms can cause massive epithelial cell damage associated with concomitant alteration of the electrolyte balance.
Assuntos
Surtos de Doenças/veterinária , Doenças dos Peixes/microbiologia , Piscirickettsia/imunologia , Infecções por Piscirickettsiaceae/microbiologia , Tilápia , Animais , Aquicultura , Colômbia/epidemiologia , Doenças dos Peixes/epidemiologia , Doenças dos Peixes/patologia , Brânquias/microbiologia , Brânquias/patologia , Brânquias/ultraestrutura , Histocitoquímica/veterinária , Microscopia Eletrônica de Transmissão/veterinária , Piscirickettsia/ultraestrutura , Infecções por Piscirickettsiaceae/epidemiologia , Infecções por Piscirickettsiaceae/patologiaRESUMO
We report a novel genetically different small infective variant of the fish pathogen Piscirickettsia salmonis (sP.s). sP.s variants were recovered both from ageing post-infected CHSE-214 culture cells as well as from naturally infected fish. The ITS region of sP.s variants, although sharing a common core sequence, is different from the ITS of the prototype strain LF-89 from which they originate. Thus, sP.s can be selectively amplified with sequence-specific discriminatory set of PCR primers. Transcriptionally, sP.s are fully active as shown by reverse transcription PCR analysis. Immunologically, sP.s is specifically recognized by antibodies against standard P. salmonis. Structurally, atomic force microscopy shows that sP.s. is well below (<0.2microm) the standard range size described for this pathogen (0.5-1.5microm). Functionally, although sP.s is infective their in vitro progeny is a hundred percent identical to the LF-89 prototype strain. In summary sP.s, represent selectable infective variants of the LF-89 strain and not new strains, probably resulting from a survival strategy of the bacteria in response to limiting growth conditions. In this frame, sP.s could be responsible of horizontal infection of fish in the field.