Subject(s)
Fish Diseases , Veterinary Medicine , Animals , Fishes , France , History, 20th Century , History, 21st Century , Veterinary Medicine/historyABSTRACT
Health control is a major issue in animal breeding and a better knowledge of the genetic bases of resistance to diseases is needed in farm animals including fish. The detection of quantitative trait loci (QTL) will help uncovering the genetic architecture of important traits and understanding the mechanisms involved in resistance to pathogens. We report here the detection of QTL for resistance to Viral Haemorrhagic Septicaemia Virus (VHSV), a major threat for European aquaculture industry. Two induced mitogynogenetic doubled haploid F2 rainbow trout (Oncorhynchus mykiss) families were used. These families combined the genome of susceptible and resistant F0 breeders and contained only fully homozygous individuals. For phenotyping, fish survival after an immersion challenge with the virus was recorded, as well as in vitro virus replication on fin explants. A bidirectional selective genotyping strategy identified seven QTL associated to survival. One of those QTL was significant at the genome-wide level and largely explained both survival and viral replication in fin explants in the different families of the design (up to 65% and 49% of phenotypic variance explained respectively). These results evidence the key role of innate defence in resistance to the virus and pave the way for the identification of the gene(s) responsible for resistance. The identification of a major QTL also opens appealing perspectives for selective breeding of fish with improved resistance.
Subject(s)
Genome , Hemorrhagic Septicemia, Viral/genetics , Immunity, Innate/genetics , Novirhabdovirus/physiology , Oncorhynchus mykiss/genetics , Quantitative Trait Loci/immunology , Animals , Aquaculture , Chromosome Mapping , Female , Genotype , Hemorrhagic Septicemia, Viral/immunology , Hemorrhagic Septicemia, Viral/mortality , Hemorrhagic Septicemia, Viral/virology , Homozygote , Male , Oncorhynchus mykiss/immunology , Oncorhynchus mykiss/virology , Phenotype , Survival Rate , Tissue Culture Techniques , Virus ReplicationABSTRACT
The merit of a candidate criterion of resistance to viral haemorrhagic septicaemia virus (VHSV) was tested with the view of producing experimental trout progeny with a predictable level of resistance. The criterion, the measure of in vitro viral replication in excised fin tissue (VREFT) was previously developed. Three experiments were performed, using both ordinary and homozygous doubled-haploid breeders. A set of 48 progeny was tested. Breeders were individually scored for repeated measures of VREFT, and the progeny were tested against VHSV (strain 07-71, serotype 1) through a waterborne challenge (5 x 10(4) pfu ml(-1) during 2 h). Analysis of repeated measures of VREFT revealed the risk of identifying 'false' resistant individuals. The highest value should be considered the most predictive of the resistance status. Survival of progeny ranged from 0 to 100% according to the group and the experiment. The survival was correlated to the mean VREFT value of the breeders in Expts 1 and 2 (R = 0.96 and 0.61 respectively), but not in Expt 3 (R = 0.36, ns) where all tested progeny were highly susceptible. Results thus indicate that viral growth in fin tissue is genetically correlated to resistance to waterborne disease and may be used to produce selected progeny, at least at the experimental scale. Possible implications of the relationship between VREFT and resistance for the study of resistance mechanisms are discussed.
Subject(s)
Culture Techniques/veterinary , Genetic Predisposition to Disease , Hemorrhagic Septicemia, Viral/genetics , Novirhabdovirus/pathogenicity , Oncorhynchus mykiss/virology , Animals , Breeding , Extremities , Female , Hemorrhagic Septicemia, Viral/immunology , Hemorrhagic Septicemia, Viral/mortality , Male , Novirhabdovirus/immunology , Oncorhynchus mykiss/immunology , Statistics as Topic , Survival Analysis , Virus ReplicationABSTRACT
Inbred lines differentially susceptible to diseases are a powerful tool to get insights into the mechanisms of genetic resistance to pathogens. In fish, chromosome manipulation techniques allow a quick production of such homozygous lines. Using gynogenesis, we produced nine homozygous clones of rainbow trout from a domestic population (INRA Sy strain). We examined the variability between clones for resistance to two rhabdoviruses, the viral haemorrhagic septicaemia virus (VHSV) and the infectious haematopoietic necrosis virus (IHNV). Intraperitoneal injections and waterborne infections were performed in parallel for both viruses. No survival was recorded after intraperitoneal injection of VHSV or IHNV, indicating that fish from all clones were fully susceptible to both viruses by this route of infection. In contrast, the different clones showed a wide range of survival frequency after waterborne infection. The resistance levels to VHSV ranged from 0 to 99% and resistance was not abrogated when resistant and sensitive animals were mixed and subjected to waterborne infection. VHSV was recovered from 10% of resistant fish after waterborne infection, confirming that virus replication was possible in this context but effective only in a low proportion of the population. The different clones also exhibited a wide range of survival (0-68%) after a waterborne infection with IHNV. Although VHSV-resistant clones were not fully resistant to IHNV, the susceptibility to IHNV and VHSV tended to be correlated, suggesting that non-specific mechanisms common to both viruses were involved.