An outbreak of granulomatous inflammation associated with Francisella noatunensis subsp orientalis in farmed tilapia (Oreochromis niloticus x O-aureus) in China

In 2013, a novel disease was detected in tilapia (Oreochromis niloticus x O. aureus) in Guangzhou, South China. To identify the causative pathogen, we conducted histological examination, bacteria isolation, and purification, and sequenced the 16S rRNA gene of isolates. Infected fish had a large number of white granulomas in the kidney, liver, heart, and spleen. The head kidney and spleen were markedly swollen. A bacterium strain designated as gz201301 was recovered from the spleen of infected tilapia. The 16S rRNA sequence of gz201301 revealed that it was highly similar to F. noatunensis subsp. orientalis. This is the first report of a Francisella-like infection in farmed tilapia in China.