Presence of viral haemorrhagic septicaemia virus (VHSV) in the environment of virus-contaminated fish farms and processing plants.

After the first outbreak of viral haemorrhagic septicaemia virus (VHSV) in Finnish brackish water rainbow trout Oncorhynchus mykiss farms, infection spread rapidly between the farms. The infrastructure of fish farming did not take into account spreading of infectious fish diseases. To show the presence of VHSV in the environment, we tested seawater, sediment and wild blue mussels Mytilus edulis from VHSV-infected fish farms, and liquid waste from a processing plant that handled infected rainbow trout. Additionally, blue mussels were bath-challenged with VHSV (exposed to cultivated virus or naturally infected rainbow trout). To detect VHSV, virus isolation in cell culture and real-time reverse transcriptase polymerase chain reaction (qRT-PCR) were used. The virus or viral RNA was detected in sea water and in liquid waste from processing plants during wintertime when water temperature is close to 0°C and sunlight is sparse. VHSV did not appear to replicate in blue mussels in our study. Therefore, blue mussels were not considered relevant carriers of VHSV. However, traces of viral RNA were detected up to 29 d post challenge in mussels. Contact with water from processing plants handling VHSV-infected fish populations increases the risk of the disease spreading to susceptible fish populations, especially during cold and dark times of the year.

Wild fish are negligible transmitters of viral haemorrhagic septicaemia virus (VHSV) genotype Id in the VHS restriction zone in Finland.

Wild fish were suspected to be the source of reinfection by viral haemorrhagic septicaemia virus (VHSV) in Finnish brackish water rainbow trout farms located in a restriction zone regarding viral haemorrhagic septicaemia (VHS) comprising the entire Province of Åland, Baltic Sea, in the 2000s. Altogether, 1636 wild fish of 17 different species living in the vicinity of infected fish farms were screened for VHSV during the years 2005-2008. Additionally, 2 uninfected wild fish species as well as farmed whitefish were introduced into a VHS-positive fish farm to test whether they became infected by VHSV from the clinically diseased rainbow trout. Wild fish did not test positive for VHSV on any occasion. In contrast, whitefish introduced to a VHS-positive farm were infected with VHSV genotype Id and started to replicate the virus for a short time during the trial. Whitefish are farmed together with, or in the vicinity of, farmed rainbow trout in the study area and, according to this study, are a possible source of the recurring infection in the restriction area. A sprivivirus was isolated from all fish species in the infection trial without causing mortality in the test groups.

Viral haemorrhagic septicaemia virus (VHSV Id) infections are detected more consistently using syndromic vs. active surveillance.

The eradication of viral haemorrhagic septicaemia virus (VHSV Id) from Finnish brackish-water rainbow trout Oncorhynchus mykiss farms located in the restriction zone in the Province of Åland, Baltic Sea, failed several times in the 2000s. The official surveillance programme was often unable to find VHSV-positive populations, leading to the misbelief in the fish farming industry that virus eradication could be achieved. The ability of 3 other surveillance programmes to detect infected fish populations was compared with the official programme. One programme involved syndromic surveillance based on the observation of clinical disease signs by fish farmers, while 2 programmes comprised active surveillance similar to the official programme, but included increased sampling frequencies and 2 additional tests. The syndromic surveillance concentrated on sending in samples for analysis when any sign of a possible infectious disease at water temperatures below 15°C was noticed. This programme clearly outperformed active surveillance. A real-time reverse transcriptase-polymerase chain reaction method proved to be at least as sensitive as virus isolation in cell culture in detecting acute VHSV infections. An ELISA method was used to test fish serum for antibodies against VHSV. The ELISA method may be a useful tool in VHSV eradication for screening populations during the follow-up period, before declaring an area free of infection.

Infectious pancreatic necrosis virus (IPNV) strain with genetic properties associated with low pathogenicity at Finnish fish farms.

Infectious pancreatic necrosis (IPN) is a contagious viral disease of fish that causes economic losses in aquaculture worldwide. In Finland, IPN virus (IPNV) has been isolated since 1987 from adult fish showing no signs of clinical disease at fish farms located in the coastal areas of the Baltic Sea. The inland area of Finland, however, remained free of IPN until 2012, when fish on several rainbow trout farms were diagnosed IPNV-positive. The fish mortalities detected at the farms were low, but clinical signs and histopathological changes typical for IPNV infection were seen in juvenile salmonids. IPNV was isolated at high water temperatures up to 22°C. In 2013 and 2014, IPNV detections continued at inland farms, indicating that infections have spread. The aim of this study was to describe the epidemiology of the outbreak and to characterise the Finnish inland IPNV isolates using histopathological, immunohistochemical and genetic approaches. In order to determine the epidemiological origin of the inland IPNV infections, the partial viral capsid protein (VP2) gene sequences of the inland IPNV isolates were compared with the sequences of the isolates from the coastal farms. Based on the genetic analysis, the inland isolates belong to IPNV Genogroup 2 (Serotype A3/Ab), and the origin of the isolates appears to be one or several coastal fish farms.

Vaccinating parent flocks against colibacillosis reduces broiler mortality - A retrospective observational study from 2016 to 2019 in Finland.

Colibacillosis is one of the most important infectious diseases in modern poultry production. The complex nature of colibacillosis has made it challenging to produce an effective vaccine. As a control measure for colibacillosis outbreak in Finland, a vaccination program with a commercial colibacillosis vaccine and later also an autogenous vaccine was started for parent flocks in 2017. In this retrospective observational study from years 2016-2019, we evaluated first week and total mortality of broiler flocks (n= 6969) originating from parents with different colibacillosis vaccination status. Broiler flocks were divided into three groups according to vaccination status of their parent flocks. First group were flocks from parents with no colibacillosis vaccines; second group was flocks from parents vaccinated with commercial vaccine only; and third group was flocks from parents with both commercial and autogenous vaccine. Bayesian modelling was used to predict posterior distributions of first week mortality and total mortality of the broiler flocks. Results of the modelling revealed that broiler flocks from unvaccinated parents had the highest mortality rates (mean first week mortality 1.40 % and mean total mortality 4.33 %, respectively) whereas flocks from parents with a combination of commercial and autogenous vaccinations had the lowest mortality rates (mean first week mortality 0,91 % and mean total mortality 3,14 %). The mortalities from broilers flocks from parents with only commercial vaccine fell in between these groups. Also, standard deviations of mortality rates were lower in broilers from parents with commercial or both vaccines. This demonstrates that in addition to lowering the mean mortality rates, the vaccinations made high mortality broiler flocks less common. Best performance was obtained when autogenous vaccine was combined to the commercial vaccine. The autogenous vaccine consists of the same type of Escherichia coli strain that was causing most colibacillosis cases during the study period in Finland. This study adds to the evidence of benefits of colibacillosis vaccines during outbreaks. It also demonstrates the importance of the knowledge of the types of APEC strains causing outbreaks to produce effective autogenous vaccines.

Mapping of QTL affecting incidence of blood and meat inclusions in egg layers.

BACKGROUND: Occurrence of blood and meat inclusions is an internal egg quality defect. Mass candling reveals most of the spots, but because brown eggshell hampers selection in brown chicken lines it has not been possible to eliminate the defect by selection. Estimated frequency of blood and meat inclusions in brown layers is about 18% whereas it is 0.5% in white egg layers. Several factors are known to increase the incidence of this fault: genetic background, low level of vitamin A and/or D, stress or infections, for instance. To study the genetic background of the defect, a mapping population of 1599 F2 hens from a cross of White Rock and Rhode Island Red lines was set up. RESULTS: Our histopathological analyses show that blood spots consist of mainly erythrocytes and that meat spots are accumulations of necrotic material. Linkage analysis of 27 chromosomes with 162 microsatellite markers revealed one significant quantitative trait locus (QTL) affecting blood spot and meat spot frequency. We sequenced a fragment of a candidate gene within the region, ZO-2, coding for a tight junction protein. Nine polymorphisms were detected and two of them were included in fine-mapping and association analysis. Fine-mapping defined the QTL result. To further verify the QTL, association analyses were carried out in two independent commercial breeding lines with the marker MCW241 and surrounding SNPs. Association was found mainly in a 0.8 Mb-wide chromosomal area on GGAZ. CONCLUSIONS: There was good agreement between the location of the QTL region on chromosome Z and the association results in the commercial breeds analyzed. Variations found in tight junction protein ZO-2 and microRNA gga-mir-1556 may predispose egg layers to blood and meat spot defects. This paper describes the first results of detailed QTL analyses of the blood and meat spots trait(s) in chickens.

Prevalence of a single fish-pathogenic Saprolegnia sp. clone in Finland and Sweden.

Thirty-one isolates of Saprolegnia sp., most originating from infected salmon or trout, were characterised genetically and physiologically. The majority (6 of 31) of the isolates from several widely separated geographical locations was found to be genetically almost identical as assessed by RAPD-PCR. The remaining isolates belonged to 3 different groups with 1 to 3 representatives each. It is suggested that the first group of isolates represents a virulent form of the organism that has been widely spread by clonal propagation. The ability to repeated zoospore emergence, as an alternative to direct germination, seems to characterise specific Saprolegnia genotypes that may have adapted to certain hosts.