<it>Francisella </it>infections in farmed and wild aquatic organisms

• Main Authors: Colquhoun Duncan J, Duodu Samuel
• Format: Article
• Language: English
• Published: BMC 2011-03-01
• Series: Veterinary Research
• Online Access: http://www.veterinaryresearch.org/content/42/1/47

<p>Abstract</p> <p>Over the last 10 years or so, infections caused by bacteria belonging to a particular branch of the genus <it>Francisella </it>have become increasingly recognised in farmed fish and molluscs worldwide. While the increasing incidence of diagnoses may in part be due to the development and widespread availability of molecular detection techniques, the domestication of new organisms has undoubtedly instigated emergence of clinical disease in some species. Francisellosis in fish develops in a similar fashion independent of host species and is commonly characterised by the presence of multi-organ granuloma and high morbidity, with varying associated mortality levels. A number of fish species are affected including Atlantic cod, <it>Gadus morhua</it>; tilapia, <it>Oreochromis </it>sp.; Atlantic salmon, <it>Salmo salar</it>; hybrid striped bass, <it>Morone chrysops </it>× <it>M. saxatilis </it>and three-lined grunt, <it>Parapristipoma trilinineatum</it>. The disease is highly infectious and often prevalent in affected stocks. Most, if not all strains isolated from teleost fish belong to either <it>F. noatunensis subsp. orientalis </it>in warm water fish species or <it>Francisella noatunensis </it>subsp. <it>noatunensis </it>in coldwater fish species. The disease is quite readily diagnosed following histological examination and identification of the aetiological bacterium by culture on cysteine rich media or PCR. The available evidence may indicate a degree of host specificity for the various <it>Francisella </it>strains, although this area requires further study. No effective vaccine is currently available. Investigation of the virulence mechanisms and host response shows similarity to those known from <it>Francisella tularensis </it>infection in mammals. However, no evidence exists for zoonotic potential amongst the fish pathogenic <it>Francisella</it>.</p>