Abstract
Infectious salmon anemia virus (ISAV) infection is currently detected by fish sampling for PCR and immunohistochemistry analysis. As an alternative to sampling fish, we evaluated two different membrane filters in combination with four buffers for elution, concentration, and detection of ISAV in seawater, during a bath challenge of Atlantic salmon (Salmo salar L.) post-smolts with high and low concentrations of ISAV. Transmission of ISAV in the bath challenge was confirmed by a high mortality, clinical signs associated with ISA disease, and detection of ISAV RNA in organ tissues and seawater samples. The electronegatively charged filter, combined with lysis buffer, gave significantly higher ISAV RNA detection by droplet digital PCR from seawater (5.6 × 104 ISAV RNA copies/L; p < 0.001). Viral shedding in seawater was first detected at two days post-challenge and peaked on day 11 post-challenge, one day before mortalities started in fish challenged with high dose ISAV, demonstrating that a large viral shedding event occurs before death. These data provide important information for ISAV shedding that is relevant for the development of improved surveillance tools based on water samples, transmission models, and management of ISA.
Highlights
Infectious salmon anemia virus (ISAV) is a water-borne virus that causes infectious salmon anemia (ISA) disease in Atlantic salmon (Salmo salar L.) [1,2,3,4]
That were used to monitor survival, fish mortality started at 12 days post challenge (DPC) in high dose group (HDg) ISAV exposed individuals and peaked at 21 DPC, with a cumulative mortality of 100%, as shown in
Initial signs of disease onset in HDg ISAV exposed individuals were observed at 9 DPC, including change in behavioral patterns, such as swimming near the surface of the tank, loss of balance, lethargy, and lack of response to stimuli
Summary
Infectious salmon anemia virus (ISAV) is a water-borne virus that causes infectious salmon anemia (ISA) disease in Atlantic salmon (Salmo salar L.) [1,2,3,4]. HPR0 ISAV does not give clinical disease, but causes a short, transient gill epithelial infection [13]. The HPR-deleted ISAV causes generalized and lethal disease which is characterized by anemia, circulatory disturbances, and bleedings in several organs of the fish [14], with cumulative mortality in infected marine fish populations varying from 0 to. Since the major ISA epidemic in Norway in the 1990s, ISAV remains a serious fish pathogen, probably because of asymptomatic infections in wild and farmed Atlantic salmon with HPR0, and the potential for emergence of new virulent strains [8]. In Norway, from one to 20 ISA outbreaks occur annually, with most of the outbreaks clustering in northern Norway during past years [16]
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