title: First identification of Francisella noatunensis subsp. orientalis causing mortality in Mexican tilapia Oreochromis spp.
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.
authors: Centro 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.
authors: Cesar
authors: C
authors: Ortega
authors: Gerardo
authors: G
authors: Mancera
authors: Ricardo
authors: R
authors: Enríquez
authors: Augusto
authors: A
authors: Vargas
authors: Simón
authors: S
authors: Martínez
authors: Raúl
authors: R
authors: Fajardo
authors: Ruben
authors: R
authors: Avendaño-Herrera
authors: María José
authors: MJ
authors: Navarrete
authors: Alex
authors: A
authors: Romero
mesh_terms: D000818:Animals; D017756:Aquaculture; D004269:DNA, Bacterial / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D005393:Fish Diseases / Q000453:epidemiology / Q000382:microbiology*; D005603:Francisella / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D016905:Gram-Negative Bacterial Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D008800:Mexico / Q000453:epidemiology; D010802:Phylogeny; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017210:Tilapia
chemical_list: D004269:DNA, Bacterial; D021903:DNA, Ribosomal Spacer; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S