Effects of temperature and salt concentration on Francisella noatunensis subsp. orientalis infections in Nile tilapia Oreochromis niloticus

Abstract

Little is known about the environmental conditions that allow Francisella noatunensis subsp. orientalis, a worldwide emergent bacterial fish pathogen, to colonize and infect wild and cultured fish. We evaluated the effect of temperature and salinity on the infectivity of F. noatunensis subsp. orientalis in Nile tilapia Oreochromis niloticus (L). Immersion challenges of tilapia with F. noatunensis subsp. orientalis at water temperatures of 25 and 30°C in both sea and fresh water were conducted for 14 d. Morbidity and mortality were recorded daily, and at the completion of the study, a quantitative assessment of the splenic bacterial burden was performed in surviving fish. Fish maintained at 25°C developed francisellosis and had considerably higher mortality and splenic bacterial concentrations compared to control fish and fish maintained at 30°C. Moreover, increasing the water temperature from 25 to 30°C prevented the development of clinical signs and mortality in Francisella-challenged fish. In conclusion, temperature significantly influenced the development of francisellosis in tilapia, whereas salinity had no effect. Our findings may be useful in the establishment of improved prophylactic practices and in the management of outbreaks of francisellosis in the aquaculture industry. KEY WORDS: Francisellosis · Aquaculture · Environment · Pathogenesis Resale or republication not permitted without written consent of the publisherDis Aquat Org 101: [217][218][219][220][221][222][223] 2012 vention and treatment of piscine francisellosis makes it an important economic and health concern amongst aquaculturists.The combination of a pathogen in the water, a susceptible host, and an unfavorable environment defines the pathogenesis of many fish infectious diseases (Snieszko 1973, Plumb & Hanson 2011. Fish are completely dependent upon water to breathe, feed, excrete wastes, maintain osmolality, and reproduce. In this sense, the physical and chemical qualities of the aquatic environment in general, and the water in particular, are critical to understanding the pathogenesis of fish diseases and to developing efficacious preventative practices and successful therapies. Due to the emergent nature of francisellosis in warm-and coldwater fish, little is known of the ecology of this bacterium in water. Moreover, to develop an in-depth understanding of the pathogenesis of Francisella noa tunensis subsp. orientalis infection, one must understand the environmental conditions that optimize the survival, infectivity, and pathogenicity of this bacterium in the fish host. Our objectives were to evaluate the capability of F. noatunensis subsp. orientalis to infect tilapia at different temperatures and sali nities, and to evaluate the survivability of la tently infected tilapia under different environmental conditions. MATERIALS AND METHODS Bacterial strains and growth conditionsFrancisella noatunensis subsp. orientalis LADL 07-285A was isolated from cultured tilapia (Oreochromis sp.) as described previously (Soto et al. 2009b...

Outbreaks and genetic diversity of Francisella noatunensis subsp orientalis isolated from farm-raised Nile tilapia (Oreochromis niloticus) in Brazil

“…In a previous study, fish reared at a water temperature of 25°C developed francisellosis that resulted in considerably higher mortality than that observed in those reared at 30°C (Soto et al, 2012c). Mauel et al (2003) also reported higher mortality among tilapia reared at an average water temperature of 24.45°C, compared with that observed among fish reared at 26.96°C.…”

PRIMEIRO RELATO DE Francisella noatunensis SUBESPÉCIE ORIENTALIS NO SUL DO BRASIL – RELATO DE CASO

“…Essa casuística corrobora com Soto et al (2012) que ao elevar a temperatura de 25 a 30°C preveniu o desenvolvimento de sinais clínicos e mortalidade nos peixes desafiados com F. noatunensis. Segundo esse agente patogênico têm a capacidade de produzir biofilme, além de sobreviver a diferentes salinidades (0 a 35 ‰), que dificulta o desenvolvimento de estratégias de prevenção, tratamento e erradicação desse patógeno emergente.…”

Molecular detection of Francisella noatunensis subsp. orientalis in cultured Nile tilapia (Oreochromis niloticus L.) in three Brazilian states

“…). At the time of this report, the status of Fno in Brazil was unknown and because of its fastidious nature may have been mistakenly unreported (Soto, Abrams & Revan ).…”