Characterization of Francisella noatunensis subsp. orientalis isolated from Nile tilapia Oreochromis niloticus farmed in Lake Yojoa, Honduras

Francisella noatunensis subsp. orientalis (Fno) is a Gram-negative, pleomorphic, facultative intracellular bacterial pathogen affecting a variety of cultured and wild fish species. Outbreaks of piscine francisellosis in warmwater fish have been documented worldwide; however, reports of Fno from Central America have been limited to a single documented outbreak in cultured tilapia in Costa Rica in 2007. From 2015 to 2017, Fno was consistently recovered from disease outbreaks in Nile tilapia Oreochromis niloticus cultivated in floating cages in Lake Yojoa, Honduras. Mortality rates during these outbreaks ranged from 50 to 85%. Fno was isolated by aerobic culture on selective media and identity confirmed by Fno-specific PCR. Repetitive extragenic palindromic PCR analysis revealed that the case isolates were genetically homogeneous with archived strains recovered from epizootics in cultured tilapia from Costa Rica and Mexico, suggesting the same strain of Fno was responsible for these otherwise unrelated fish kills. The current study provides only the second report of Fno in Central America and characterizes the first Fno outbreak in cultured fish in Honduras.