DAO 120:205-215 (2016)  -  DOI: https://doi.org/10.3354/dao02999

First identification of Francisella noatunensis subsp. orientalis causing mortality in Mexican tilapia Oreochromis spp.

Cesar Ortega1,*, Gerardo Mancera1, Ricardo Enríquez2, Augusto Vargas2,3, Simón Martínez1, Raúl Fajardo1, Ruben Avendaño-Herrera3,4,5, María José Navarrete2, Alex Romero2,3 

1Centro de Investigación y Estudios Avanzados en Salud Animal (CIESA), Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma del Estado de México, Carretera Toluca-Atlacomulco Km. 15.5, Toluca 50200, Mexico
2Laboratorio de Biotecnología y Patología Acuática, Instituto de Patología Animal, Facultad de Ciencias Veterinarias, Campus Isla Teja, Universidad Austral de Chile, Independencia 641, Valdivia 5090000, Chile
3Centro FONDAP, Interdisciplinary Center for Aquaculture Research (INCAR), PO Box 160-C, Concepción 4030000, Chile
4Laboratorio de Patología de Organismos Acuáticos y Biotecnología Acuícola, Facultad de Ciencias Biológicas, Universidad Andrés Bello, 2520000 Viña del Mar, Chile
5Centro de Investigación Marina Quintay (CIMARQ), Universidad Andres Bello, Quintay, Chile
*Corresponding author:

ABSTRACT: Francisellosis, an emerging disease in tilapia Oreochromis spp., is caused by the facultative, intracellular bacterium Francisella noatunensis subsp. orientalis, which is present in various countries where tilapia farming is commercially important. We confirmed the presence of francisellosis in Mexican tilapia cultures in association with an outbreak during the second semester of 2012. Broodstock fish presented a mortality rate of approximately 40%, and disease was characterized by histologically classified granulomas, or whitish nodules, in different organs, mainly the spleen and kidney. Through DNA obtained from infected tissue and pure cultures in a cysteine heart medium supplemented with hemoglobin, F. noatunensis subsp. orientalis was initially confirmed through the amplification and analysis of the 16S rRNA gene and the internal transcribed spacer region. Phylogenetic analysis of these genes demonstrated close similarity with previously reported F. noatunensis subsp. orientalis sequences obtained from infected tilapia from various countries. The identification of this subspecies as the causative agent of the outbreak was confirmed using the iglC gene as a target sequence, which showed 99.5% identity to 2 F. noatunensis subsp. orientalis strains (Ethime-1 and Toba04). These findings represent the first documented occurrence of francisellosis in Mexican tilapia cultures, which highlights the importance of establishing preventative measures to minimize the spread of this disease within the Mexican aquaculture industry.

KEY WORDS: Francisellosis · Freshwater aquaculture · Mexico · Tilapia

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Cite this article as: Ortega C, Mancera G, Enríquez R, Vargas A and others (2016) First identification of Francisella noatunensis subsp. orientalis causing mortality in Mexican tilapia Oreochromis spp.. Dis Aquat Org 120:205-215. https://doi.org/10.3354/dao02999

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