Multiple-locus, variable number of tandem repeat analysis (MLVA) of the fish-pathogen Francisella noatunensis

<p>Abstract</p> <p>Background</p> <p>Since <it>Francisella noatunensis </it>was first isolated from cultured Atlantic cod in 2004, it has emerged as a global fish pathogen causing disease in both warm and cold water species. Outbreaks of francisellosis occur in several important cultured fish species making a correct management of this disease a matter of major importance. Currently there are no vaccines or treatments available. A strain typing system for use in studies of <it>F. noatunensis </it>epizootics would be an important tool for disease management. However, the high genetic similarity within the <it>Francisella </it>spp. makes strain typing difficult, but such typing of the related human pathogen <it>Francisella tullarensis </it>has been performed successfully by targeting loci with higher genetic variation than the traditional signature sequences. These loci are known as Variable Numbers of Tandem Repeat (VNTR). The aim of this study is to identify possible useful VNTRs in the genome of <it>F. noatunensis</it>.</p> <p>Results</p> <p>Seven polymorphic VNTR loci were identified in the preliminary genome sequence of <it>F. noatunensis </it>ssp. <it>noatunensis </it>GM2212 isolate. These VNTR-loci were sequenced in <it>F. noatunensis </it>isolates collected from Atlantic cod (<it>Gadus morhua</it>) from Norway (n = 21), Three-line grunt (<it>Parapristipoma trilineatum</it>) from Japan (n = 1), Tilapia (<it>Oreochromis </it>spp.) from Indonesia (n = 3) and Atlantic salmon (<it>Salmo salar</it>) from Chile (n = 1). The Norwegian isolates presented in this study show both nine allelic profiles and clades, and that the majority of the farmed isolates belong in two clades only, while the allelic profiles from wild cod are unique.</p> <p>Conclusions</p> <p>VNTRs can be used to separate isolates belonging to both subspecies of <it>F. noatunensis</it>. Low allelic diversity in <it>F. noatunensis </it>isolates from outbreaks in cod culture compared to isolates wild cod, indicate that transmission of these isolates may be a result of human activity. The sequence based MLVA system presented in this study should provide a good starting point for further development of a genotyping system that can be used in studies of epizootics and disease management of francisellosis.</p

Comédie Française. , Melle Favart, rôle d'Hiras dans Cléopâtre : [photographie] / J. V. de Villeneuve

Abstract Background The myxosporean parasite Parvicapsula pseudobranchicola commonly infects farmed Atlantic salmon in northern Norway. Heavy infections are associated with pseudobranch lesions, runting and mortality in the salmon populations. The life-cycle of the parasite is unknown, preventing controlled challenge experiments. The infection dynamics, duration of sporogony, tissue tropism and ability to develop immunity to the parasite in farmed Atlantic salmon is poorly known. We conducted a field experiment, aiming at examining these aspects. Methods Infections in a group of Atlantic salmon were followed from before sea-transfer to the end of the production (604 days). Samples from a range of tissues/sites were analysed using real-time RT-PCR and histology, including in situ hybridization. Results All salmon in the studied population rapidly became infected with P. pseudobranchicola after sea-transfer medio August. Parasite densities in the pseudobranchs peaked in winter (November-January), and decreased markedly to March. Densities thereafter decreased further. Parasite densities in other tissues were low. Parasite stages were initially found to be intravascular in the pseudobranch, but occurred extravascular in the pseudobranch tissue at 3 months post-sea-transfer. Mature spores appeared in the pseudobranchs in the period with high parasite densities in the winter (late November-January), and were released (i.e. disappeared from the fish) in the period January-March. Clinical signs of parvicapsulosis (December-early February) were associated with high parasite densities and inflammation in the pseudobranchs. No evidence for reinfection was seen the second autumn in sea. Conclusions The main site of the parasite in Atlantic salmon is the pseudobranchs. Blood stages occur, but parasite proliferation is primarily associated with extravascular stages in the pseudobranchs. Disease and mortality (parvicapsulosis) coincide with the completion of sporogony. Atlantic salmon appears to develop immunity to P. pseudobranchicola. Further studies should focus on the unknown life-cycle of the parasite, and the pathophysiological effects of the pseudobranch infection that also could affect the eyes and vision