Efficacy and safety of an inactivated vaccine against Salmonid alphavirus (family Togaviridae).

Pancreas disease (PD) in salmonid fish is caused by an infection with Salmonid alphavirus (SAV) and remains as one of the major health problems in the European fish farming industry. Sequence studies have revealed a genetic diversity among viral strains. A subtype of SAV (SAV3) is causing an epizootic in farmed salmonids in Norway. Here we evaluate efficacy and safety of an inactivated virus vaccine based on ALV405, a strain of SAV3 that was isolated from Norwegian salmon. The vaccine provided an average relative percent survival (RPS) of 98.5 in an intraperitoneal challenge model, and induced nearly total protection against PD in a cohabitant challenge model. It provided significant protection against SAV-induced mortality also in a field trial under industrial conditions. Local reactions seen as melanization and adhesions in the visceral cavity were less severe than those induced by two commercial vaccines. Finally, we demonstrated that the protection is not impaired when the ALV405 antigen is combined with other viral or bacterial antigens in a polyvalent vaccine. The results confirm that efficient and safe protection against SAV infection and development of PD is possible using an inactivated virus vaccine, both alone and as a component in a polyvalent vaccine.

Atlantic salmon reovirus infection causes a CD8 T cell myocarditis in Atlantic salmon (Salmo salar L.).

Heart and skeletal inflammation (HSMI) of farmed Atlantic salmon (Salmo salar L.) is a disease characterized by a chronic myocarditis involving the epicardium and the compact and spongious part of the heart ventricle. Chronic myositis of the red skeletal muscle is also a typical finding of HSMI. Piscine reovirus (PRV) has been detected by real-time PCR from farmed and wild salmon with and without typical changes of HSMI and thus the causal relationship between presence of virus and the disease has not been fully determined. In this study we show that the Atlantic salmon reovirus (ASRV), identical to PRV, can be passaged in GF-1 cells and experimental challenge of naïve Atlantic salmon with cell culture passaged reovirus results in cardiac and skeletal muscle pathology typical of HSMI with onset of pathology from 6 weeks, peaking by 9 weeks post challenge. ASRV replicates in heart tissue and the peak level of virus replication coincides with peak of heart lesions. We further demonstrate mRNA transcript assessment and in situ characterization that challenged fish develop a CD8+ T cell myocarditis.

Persistence of antibodies in blood and body fluids in decaying fox carcasses, as exemplified by antibodies against Microsporum canis.

To assist in evaluating serological test results from dead animals, 10 silver foxes (Vulpes vulpes) and 10 blue foxes (Alopex lagopus), 6 of each species previously vaccinated against and all challenged with Microsporum canis, were blood sampled and euthanased. Fox carcasses were stored at +10 degrees C, and autopsy was performed on Days 0, 2, 4, 7, and 11 post mortem during which samples from blood and/or body fluid from the thoracic cavity were collected. Antibodies against M. canis were measured in an enzyme-linked immunosorbent assay (ELISA) as absorbance values (optical density; OD). To assess the degradation of antibodies, the ratio between post mortem and ante mortem absorbance was calculated. The mean absorbance from samples collected during autopsy was generally lower than from samples from live animals. In blood samples, this difference increased significantly with time (P = 0.04), while in body fluid samples the difference decreased (not significant; P = 0.18). We suggest that a positive serological result from testing blood or body fluid of a dead animal may be regarded as valuable, although specific prevalences obtained by screening populations based on this type of material may represent an under-estimation of the true antibody prevalence. Negative serological test results based on material from carcasses may be less conclusive, taken into account the general degradation processes in decaying carcasses, also involving immunoglobulin proteins.