Abstract

Infectious salmon anemia (ISA) is a severe disease that affects farmed Atlantic salmon (Salmo salar), causing outbreaks in sea water in most salmon-producing countries worldwide and with particular aggressiveness in southern Chile. The etiological agent of the disease is a virus belonging to the Orthomyxoviridae family, named the Infectious Salmon Anemia Virus (ISAV). Although it has been suggested that the virus can be vertically transmitted, even in fresh water, there is a lack of compelling experimental evidence to confirm this. Here we demonstrate that two brood stock female adult specimens that harbored the virus systemically, though without clinical signs, significant levels of putative viral loads in their ovarian fluid as well as in the eggs. The target virus corresponded to an HPR-3 variant, which is known to be virulent in seawater and responsible for recent and past outbreaks of the disease in Chile. Additionally, the virus recovered from the fluid as well as from the interior of the eggs, was fully infective to a susceptible fish cell line. To our knowledge, this is the first robust evidence demonstrating on the one hand, mother-to-offspring vertical transmission of the infective virus; and on the other, the asymptomatic transmission of a virulent form of the virus in freshwater fish.