Francisella sp., an emerging pathogen of tilapia, Oreochromis niloticus (L.), in Costa Rica

Esteban Soto Martinez, J. P. Hawke, D. Fernandez, J. A Morales

Research output: Contribution to journalArticlepeer-review

111 Scopus citations


Francisella sp. is an emergent bacterial pathogen that causes acute to chronic disease in warm and cold water cultured and wild fish species. During the past 3 years, the bacterium has been detected in tilapia, Oreochromis niloticus, cultured in Costa Rica. Infected fish presented non-specific clinical signs, such as erratic swimming, anorexia, anaemia, exophthalmia and high mortality. Upon macroscopic and microscopic examination, several internal organs (mainly spleen and kidney) were enlarged and contained white nodules. Histological examination revealed the presence of multifocal granulomatous lesions, with the presence of numerous small, pleomorphic, cocco-bacilli. The bacteria were isolated from infected tilapia on selective media and grown on several media with and without antibiotics. Specific PCR primers to the Francisella genus were used to confirm the preliminary diagnoses. In comparison with several bacterial 16S rRNA sequences, our isolate was found to share 99% identity with other Fransicella spp. isolated from fish, and more than 97% identity to the human pathogen Francisella tularensis. Koch's postulates were fulfilled after experimental intraperitoneal and gill exposure challenges.

Original languageEnglish (US)
Pages (from-to)713-722
Number of pages10
JournalJournal of Fish Diseases
Issue number8
StatePublished - Aug 2009
Externally publishedYes


  • Bacteria
  • Costa Rica
  • Emergent fish pathogen
  • Francisella
  • Granulomas
  • Tilapia

ASJC Scopus subject areas

  • Aquatic Science
  • veterinary (miscalleneous)


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