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The Influence of Infective Dose on the Virulence of a Generalist Pathogen in Rainbow Trout (Oncorhynchus mykiss) and Zebra Fish (Danio rerio).

Kinnula H, Mappes J, Valkonen JK, Sundberg LR - PLoS ONE (2015)

Bottom Line: We studied how an infective dose in an environmentally transmitted opportunistic fish pathogen, Flavobacterium columnare, affects its virulence both in rainbow trout, which are frequently infected at fish farms, and in zebra fish, a host that is not naturally infected by F. columnare.Infection success (measured as host morbidity) correlated positively with dose when the hosts were exposed to the high-virulence strain, but no response for the dose increase was found when the hosts were exposed to the low-virulence strain.We suggest that as an increase in dose can lead to increased host morbidity, both the interstrain interactions and differences in infectivity in different hosts may influence the severity and consequently the evolution of disease.

View Article: PubMed Central - PubMed

Affiliation: Centre of Excellence in Biological Interactions, Department of Biological and Environmental Science, University of Jyvaskyla, Finland.

ABSTRACT
Pathogen density and genetic diversity fluctuate in the outside-host environment during and between epidemics, affecting disease emergence and the severity and probability of infections. Although the importance of these factors for pathogen virulence and infection probability has been acknowledged, their interactive effects are not well understood. We studied how an infective dose in an environmentally transmitted opportunistic fish pathogen, Flavobacterium columnare, affects its virulence both in rainbow trout, which are frequently infected at fish farms, and in zebra fish, a host that is not naturally infected by F. columnare. We used previously isolated strains of confirmed high and low virulence in a single infection and in a co-infection. Infection success (measured as host morbidity) correlated positively with dose when the hosts were exposed to the high-virulence strain, but no response for the dose increase was found when the hosts were exposed to the low-virulence strain. Interestingly, the co-infection resulted in poorer infection success than the single infection with the high-virulence strain. The rainbow trout were more susceptible to the infection than the zebra fish but, in both species, the effects of the doses and the strains were qualitatively similar. We suggest that as an increase in dose can lead to increased host morbidity, both the interstrain interactions and differences in infectivity in different hosts may influence the severity and consequently the evolution of disease. Our results also confirm that the zebra fish is a good laboratory model to study F. columnare infection.

No MeSH data available.


Related in: MedlinePlus

Estimated mortality risk per hour of A) zebra fish (Danio rerio), and B) rainbow trout (Oncorhynchus mykiss) infected with a high-virulence (continuous line) and a low-virulence (dotted line) strain of F. columnare, and their mixture, i.e. co-infection (dashed line).
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pone.0139378.g001: Estimated mortality risk per hour of A) zebra fish (Danio rerio), and B) rainbow trout (Oncorhynchus mykiss) infected with a high-virulence (continuous line) and a low-virulence (dotted line) strain of F. columnare, and their mixture, i.e. co-infection (dashed line).

Mentions: The risk of fatal infection of the host was significantly influenced by the dose, the treatment (high-virulence strain, low-virulence strain or co-infection) and the host species (Fig 1, Tables 2 and 3). We found that 1) the increase in the dose correlates positively with the host morbidity risk when the hosts are exposed to the high-virulence strain or the mixture; 2) the infection success in the co-infected hosts is approximately an average of that of hosts infected with the high-virulence and the low-virulence strains (Fig 1), indicating that only the high-virulence strain is responsible for the host morbidity; and 3) the rainbow trout is more susceptible to the columnaris infection than the zebra fish (Fig 1), but both hosts respond to the bacterial doses and strains qualitatively similarly. All the moribund hosts were found positive for F. columnare in bacterial culture taken from fish gills, whereas the unexposed hosts and hosts surviving the infection were found negative.


The Influence of Infective Dose on the Virulence of a Generalist Pathogen in Rainbow Trout (Oncorhynchus mykiss) and Zebra Fish (Danio rerio).

Kinnula H, Mappes J, Valkonen JK, Sundberg LR - PLoS ONE (2015)

Estimated mortality risk per hour of A) zebra fish (Danio rerio), and B) rainbow trout (Oncorhynchus mykiss) infected with a high-virulence (continuous line) and a low-virulence (dotted line) strain of F. columnare, and their mixture, i.e. co-infection (dashed line).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4589314&req=5

pone.0139378.g001: Estimated mortality risk per hour of A) zebra fish (Danio rerio), and B) rainbow trout (Oncorhynchus mykiss) infected with a high-virulence (continuous line) and a low-virulence (dotted line) strain of F. columnare, and their mixture, i.e. co-infection (dashed line).
Mentions: The risk of fatal infection of the host was significantly influenced by the dose, the treatment (high-virulence strain, low-virulence strain or co-infection) and the host species (Fig 1, Tables 2 and 3). We found that 1) the increase in the dose correlates positively with the host morbidity risk when the hosts are exposed to the high-virulence strain or the mixture; 2) the infection success in the co-infected hosts is approximately an average of that of hosts infected with the high-virulence and the low-virulence strains (Fig 1), indicating that only the high-virulence strain is responsible for the host morbidity; and 3) the rainbow trout is more susceptible to the columnaris infection than the zebra fish (Fig 1), but both hosts respond to the bacterial doses and strains qualitatively similarly. All the moribund hosts were found positive for F. columnare in bacterial culture taken from fish gills, whereas the unexposed hosts and hosts surviving the infection were found negative.

Bottom Line: We studied how an infective dose in an environmentally transmitted opportunistic fish pathogen, Flavobacterium columnare, affects its virulence both in rainbow trout, which are frequently infected at fish farms, and in zebra fish, a host that is not naturally infected by F. columnare.Infection success (measured as host morbidity) correlated positively with dose when the hosts were exposed to the high-virulence strain, but no response for the dose increase was found when the hosts were exposed to the low-virulence strain.We suggest that as an increase in dose can lead to increased host morbidity, both the interstrain interactions and differences in infectivity in different hosts may influence the severity and consequently the evolution of disease.

View Article: PubMed Central - PubMed

Affiliation: Centre of Excellence in Biological Interactions, Department of Biological and Environmental Science, University of Jyvaskyla, Finland.

ABSTRACT
Pathogen density and genetic diversity fluctuate in the outside-host environment during and between epidemics, affecting disease emergence and the severity and probability of infections. Although the importance of these factors for pathogen virulence and infection probability has been acknowledged, their interactive effects are not well understood. We studied how an infective dose in an environmentally transmitted opportunistic fish pathogen, Flavobacterium columnare, affects its virulence both in rainbow trout, which are frequently infected at fish farms, and in zebra fish, a host that is not naturally infected by F. columnare. We used previously isolated strains of confirmed high and low virulence in a single infection and in a co-infection. Infection success (measured as host morbidity) correlated positively with dose when the hosts were exposed to the high-virulence strain, but no response for the dose increase was found when the hosts were exposed to the low-virulence strain. Interestingly, the co-infection resulted in poorer infection success than the single infection with the high-virulence strain. The rainbow trout were more susceptible to the infection than the zebra fish but, in both species, the effects of the doses and the strains were qualitatively similar. We suggest that as an increase in dose can lead to increased host morbidity, both the interstrain interactions and differences in infectivity in different hosts may influence the severity and consequently the evolution of disease. Our results also confirm that the zebra fish is a good laboratory model to study F. columnare infection.

No MeSH data available.


Related in: MedlinePlus