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Every year, brown trout die in rivers in central Europe. But now, researchers think they have found the causative agent. Georgina Mills reports., (British Veterinary Association.)

A cross-sectional survey of 215 Grass Carp Ctenopharyngodon idella ponds was conducted in southern China between May 2010 and November 2011. An in-depth questionnaire was developed to evaluate a series of biosecurity practices, environmental factors, and management factors at the farm level. Fish samples with clinical hemorrhagic signs were also collected from each pond to assess the clinical disease of Grass Carp reovirus by using reverse transcription (RT) PCR assay. The association between the incidence of Grass Carp hemorrhagic disease (GCHD) and risk factors was analyzed using logistic regression. Of the 215 ponds, 144 showed GCHD-positive responses to RT-PCR assay. In addition, survey results revealed that inferior environmental conditions occurred in most ponds with an incidence of GCHD; such conditions included a thick mud layer; no cleansing and restoration practices (CRPs) before culture; and poor water quality (i.e., high ammonia nitrogen and nitrite concentrations and low transparency). Logistic regression model results suggested that decreased risks were associated with fry vaccination, a safe water source, and deepening of the water level, whereas increased risk factors mainly included no CRPs, excessive rearing density, disease history, and inferior water quality. Presently, control efforts are restricted to immunization of Grass Carp as the best management option for farms. Deepening the water levels and improving water sources can also effectively reduce the incidence of GCHD by diluting the pond rearing densities.

Numerous cases of tenosynovitis appeared in France causing high morbidity in free-range and standard broilers. The main clinical findings were lameness, stunting and non-uniform bodyweights. Although the natural mortality was low, the economic losses due to birds that had to be removed from the flock prematurely, downgrading of carcases and lower average weights at slaughter were substantial. Postmortem examinations, bacteriological, virological and serological examination confirmed the aetiology of avian orthoreovirus (ARV)-induced tenosynovitis. The isolated ARVs were analysed serologically and genetically. Sequencing of σC RT-PCR products and phylogenetic analysis revealed a new type of ARV. The virus was not neutralised in serum neutralisation test using monovalent sera from vaccinated chickens. Together with the flock data, epidemiology of these recent reovirus outbreaks in France was reconstructed. It is concluded that these reovirus isolates differ serologically and genetically from the well described reovirus isolates used in commercial vaccines which were not capable of preventing the disease. The outbreaks resulted in substantial losses in broilers from vaccinated breeders.

The ranavirus, epizootic hematopoietic necrosis virus (EHNV), is endemic to southern Australia with natural outbreaks resulting in mass mortality events in wild Redfin Perch Perca fluviatilis (also known as Eurasian Perch) and less severe disease in farmed Rainbow Trout Oncorhynchus mykiss. To further investigate the host range for EHNV, 12 ecologically or economically important freshwater fish species from southeastern Australia were exposed experimentally to the virus. A bath-challenge model at 18 ± 3°C was employed with limited use of intraperitoneal inoculation to determine if a species was likely to be susceptible to EHNV. Of the species tested, Murray-Darling Rainbowfish Melanotaenia fluviatilis and Dewfish Tandanus tandanus (also known as Freshwater Catfish) were considered to be potentially susceptible species. EHNV was isolated from approximately 7% of surviving Eastern Mosquitofish Gambusia holbrooki, indicating this widespread alien fish species is a potential carrier. The infection of Silver Perch Bidyanus bidyanus and Macquarie Perch Macquaria australasica and the lack of infection in Murray Cod Maccullochella peelii peelii and Golden Perch Macquaria ambigua ambigua after exposure to EHNV via water confirmed earlier data from Langdon (1989). Five other species of native fish were potentially not susceptible to the virus or the fish were able to recover during the standard 35-d postchallenge observation period. Overall, it appeared that EHNV was less virulent in the present experimental model than in previous studies, but the reasons for this were not identified. Received May 21, 2012; accepted November 1, 2012.

The present study constructed a spatial-temporal statistical model to identify the risk and protective factors for haemorrhagic disease (HD) in white-tailed deer in the five states of Alabama, Georgia, South Carolina, North Carolina and Tennessee. The response variable was binary, indicating the presence or absence of HD in an individual county, measured annually from 1983 to 2000. Predictor variables included climatic factors of temperature, rainfall, wind speed and dew point, remotely sensed data of normalised difference vegetation index (NDVI) and land surface temperature derived from archived remotely sensed advanced very-high-resolution radiometer (AVHRR) satellite data, elevation, a spatial autocorrelation (SA) term and a temporal autocorrelation term. This study first applied principal component factor analysis to reduce the volume of climatic data and remotely sensed data. Then, a generalised linear mixed model framework (GLMM) was used to develop a spatial-temporal statistical model. The results showed that the area under receiver operating characteristic curve (ROC) was 0.728, indicating a good overall fit of the model. The total prediction accuracy over the 18 year period with optimal cut-off probability was 67 per cent. The prediction accuracy for individual years ranged from 48 to 75 per cent.

The American grass carp reovirus (AGCRV) Aquareovirus G is not strongly associated with disease in fish, but it is often detected by cell culture during routine inspections of healthy fish. The cytopathic effect of AGCRV does not involve the typical syncytia associated with most aquareoviruses. Instead, the AGCRV produces a pattern of cell rounding that is very similar to that produced by rhabdoviruses, including those that are highly regulated. We have developed a quantitative polymerase chain reaction assay that can be used to identify AGCRV in cell cultures or directly on fish tissues. The assay detects as few as two copies of the plasmid template, has a coefficient of variation of 15% among assays performed on different days, and does not cross-react with any other aquareoviruses tested. Assays performed on tissues of cultured golden shiners Notemigonus crysoleucas and fathead minnow Pimephales promelas revealed a high prevalence of infection among healthy fish but no association with disease.

In February 1991 a severe haemorrhagic disease affected exotic deer aged over six months in the Al-Hofuf area of the eastern region of Saudi Arabia. The morbidity rate was 40 per cent and the case fatality rate was 60 per cent. The clinical signs were high temperature (up to 41.5 degrees C), nasal discharge, slight salivation and lacrimation, congestion of the conjunctivae, torticollis, tremors when trying to stand, recumbency and coma leading to death. Post mortem examination revealed a severe haemorrhagic disease. A virus, serologically related to the bluetongue serogroup, was isolated from the deer. Sheep and goats kept on the same farm did not show any clinical signs. The epidemiology of the outbreak is discussed.

Calf diarrhoea is an important cause of economic loss. The aetiology of the disease is considered with particular reference to the role of viruses. Although many microbial organisms have been associated with the disease, there is doubt concerning their true role as causative agents. Two viruses, neonatal calf diarrhoea reovirus-life agent and calf coronavirus, have been discovered recently which appear to play an important role in many cases of diarrhoea and the evidence for considering them to be primary causes of the disease is discussed.