An outbreak of disease caused by Francisella sp. in Nile tilapia Oreochromis niloticus at a recirculation fish farm in the UK

Abstract

This study details the first diagnosis of Francisella sp. in tilapia in the United Kingdom. Losses of tilapia fry at a recirculation fish farm in England were investigated, giving a presumptive positive diagnosis of infection with Francisella sp. by histopathological examination. Most fish sampled showed moderate to marked pathology of the major organs, with lesions being present in most tissues. The most obvious host response was granuloma formulation. A subsequent follow-up visit provided further evidence for the presence of a Francisella species. PCR amplicons were obtained using Francisella spp.-specific primers that shared 100% sequence identity with the 16S rRNA gene of the type strain of the species F. asiatica previously described as the cause of disease in tilapia in Southeast Asia and Central America. This outbreak and the subsequent investigation emphasise the importance of strict biosecurity at fish farms and the care that needs to be taken when using a new supplier of fish.

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

“…Our results are consistent with those of previous studies, which showed that Nile tilapia fingerlings are the life stage most susceptible to FNO infection (Jeffery et al, 2010;Soto et al, 2011Soto et al, , 2013. In addition, the occurrence of disease in young adult tilapia (>100g) was confirmed.…”

“…The diseased fish presented with anorexia, melanosis, exophthalmia, erratic swimming, skin ulcers, and gill pallor. These clinical signs were similar to previously described outbreaks of FNO-related francisellosis in tilapia in Central America (Mauel et al, 2007;Soto et al, 2009), Taiwan (Chen et al, 1994), Indonesia (Ottem et al, 2009), the UK (Jeffery et al, 2010), and the USA (Soto et al, 2011). Our findings represent the first report of outbreaks of FNO-related francisellosis in South America.…”

“…At some of the farms, mortality reached 60% of the total fish stocks. Previous reports of outbreaks at tilapia farms in other regions of the world did not present data for total mortality based on verified cases (Soto et al, 2009(Soto et al, , 2011Jeffery et al, 2010). Mortality rates of up to 40% in Atlantic cod have been reported for francisellosis caused by F. noatunensis subsp noatunensis (Colquhoun and Duodu, 2011), which is lower than that caused by FNO.…”

“…Cases of francisellosis caused by FNO in farm-raised tilapia have been reported in Taiwan (Chen et al, 1994), Costa Rica (Soto et al, 2009), Indonesia (Ottem et al, 2009), the UK (Jeffery et al, 2010), and the USA (Soto et al, 2011). However, data regarding FNO infections at fish farms in South America are scant.…”

The Development of Sustainable Saltwater-Based Food Production Systems: A Review of Established and Novel Concepts

“…RASs improve conditions for cultured fish by having greater control over environmental and water quality parameters and enhancement of feeding efficiency. Subsequently, RASs can allow for higher stocking densities than most aquacultural systems [91,100,[104][105][106][107][108][109][110] by sterilizing the water prior to (re)entry to the fish tanks, pathogens and contaminants are removed, reducing the risk of disease outbreaks and contaminant uptake by the fish [18,104,111]. Due to the on-land and recirculatory nature of RASs, the potential for fish escapes is greatly reduced [2,104].…”