Piscirickettsia-Like Organisms as a Cause of Acute Necrotic Lesions in Colombian Tilapia Larvae

Abstract

Abstract. 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 6 0.2 mm 3 2.1 6 0.6 mm 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.

Molecular characterization and pathogenicity of Francisella noatunensis subsp. orientalis isolated from cultured tilapia (Oreochromis sp.) in Taiwan

“…Tilapia francisellosis is a systemic visceral granulomatous disease that causes high mortality and huge economic losses in tilapia farming worldwide, including in Taiwan (Hsieh, Tung, Tu, Chang, & Tsai, ), USA (Birkbeck, Feist, & Verner‐Jeffreys, ; Colquhoun & Duodu, ; Mauel et al, ; Soto, Baumgartner, Wiles, & Hawke, ), Brazil (Leal, Tavares, & Figueiredo, ), Columbia (Iregui, Vasquez, Rey, & Verjan, ), Costa Rica (Soto, Hawke, Fernandez, & Morales, ), UK (Jeffery, Stone, Feist, & Verner‐Jeffreys, ; Ramírez‐Paredes et al, ; Shahin et al, ), Mexico (Ortega et al, ), China (Lin et al, ) and Thailand (Jantrakajorn & Wongtavatchai, ; Nguyen, Dong, Senapin, Pirarat, & Rodkhum, ). The aetiologic agent of tilapia francisellosis is a Gram‐negative facultative intracellular bacterium belonging to F. noatunensis subsp.…”

Francisella Infection in Cultured Tilapia in Thailand and the Inflammatory Cytokine Response

“…orientalis have been recognized in piscine francisellosis (Kamaishi et al 2005;Nylund et al 2006;Olsen et al 2006;Birkbeck et al 2007). In tilapia Oreochromis species, outbreaks of a systemic granulomatous condition with intracellular micro-organisms in cultured fish were first reported in Taiwan (Chern and Chao 1994), and a similar disorder was later found affecting cultured fish in Hawaii and the continental USA (Mauel et al 2003(Mauel et al , 2005, Costa Rica (Soto et al 2009), the United Kingdom (Jeffery et al 2010), Colombia (Iregui et al 2011), Brazil (Leal et al 2014), and Thailand (Nguyen et al, in press).…”

Rickettsia‐like organisms from cultured aquatic organisms, with emphasis on necrotizing hepatopancreatitis bacterium affecting penaeid shrimp: an overview on an emergent concern

“…Rickettsia‐like organisms can affect fish at their larvae, juvenile and adult phases (Iregui et al . ).…”

“…Modified from Fryer and Lannan (1994) and Mauel and Miller (2002) Host organism family (Wang & Gu 2002). Rickettsia-like organisms can affect fish at their larvae, juvenile and adult phases (Iregui et al 2011).…”