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

Abstract

ABSTRACT. Francisella noatunensis subsp orientalis (FNO) is an emerging pathogen of warm water tilapia in a number of different countries. The disease caused by this bacterium in fish is characterized by a systemic granulomatous infection that causes high mortality rates during outbreaks. FNO has been previously described in Asia, Europe, and Central and North America. Its occurrence in South America has never been described. Since 2012, outbreaks of a granulomatous disease have been recorded in cage farms of Nile tilapia (Oreochromis niloticus L.) in Brazil. The current study aimed to identify the etiologic agent of recent francisellosis outbreaks at Brazilian tilapia farms, and to characterize the genetic diversity of the pathogen from farms with distinct geographic origins and without epidemiological connections. Bacteriological analysis Francisellosis in cage-raised Nile tilapia of 44 diseased Nile tilapia collected from five cage farms in Brazil was performed during 2012 and 2013. The farms were in different locations and had no recent history of animal or biological material transport between each other. Sixty-two FNO isolates were identified on the basis of FNO-specific qPCR. The main predisposing factors for the occurrence of outbreaks on Brazilian farms were lower water temperature (<22°C) and life stage of fish, affecting mainly fry, fingerlings and young adults (live weight <100 g). The genetic diversity of the Brazilian FNO isolates was evaluated using repetitive extragenic palindromic-PCR. The isolates from different origins were shown to be clonally related. This is the first report of the occurrence and genetic diversity of FNO in South America.

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

“…Since 2012, piscine francisellosis has been associated with high mortality in Southeast and South regions of Brazilian tilapia aquaculture farms, particularly during the winter (Leal, Tavares & Figueiredo ; Assis et al . ; Jatobá, Klipp & Hoppe ).…”

Naturally concurrent infections of bacterial and viral pathogens in disease outbreaks in cultured Nile tilapia (Oreochromis niloticus) farms

“…Previously, some important pathogens devastating tilapia within intensively produced systems were reported, such as Streptococcus agalactiae (Olivares-Fuster et al, 2008;Kayansamruaj et al, 2014a;Kayansamruaj et al, 2014b), Flavobacterium columnare (Figueiredo et al 2005; press-a,b), Francisella sp. (Soto et al, 2009;Jeffery et al, 2010;Leal et al, 2014), Edwardsiella spp. (Iregui et al, 2012;Soto et al, 2012), Aeromonas spp.…”

Susceptibility of common carp and sunfish to a strain of Francisella noatunensis subsp. orientalis in a challenge experiment

“…Previous work has shown that for tilapia mortality rates can be 100% in less than 48 to 72 h (Soto et al 2009a), 86.7 ± 23% in 5 d p.i. (Nguyen et al 2016), or 90% between 20 h and 8 d (Leal et al 2014). In our study, mortality did not correlate with the infection dose.…”

“…In general, the disease follows a chronic progression characterized by the formation of multifocal white nodules in the spleen and other organs (Soto et al 2009a(Soto et al , 2012a. Mortalities can be high (Chen et al 1994, Leal et al 2014.…”