The aim of the study was to identify the genotype of Polish isolates of salmonid alphaviruses (SAV) and to find the origin of the virus. Samples for virus isolation included the kidneys, spleen, and liver pooled from 10 fish. A typical cytopathic effect was observed after inoculation of samples on cell lines. Total RNA was extracted from cell culture supernatant and submitted to RT-PCR with primers amplifying two informative regions of the genome: a conserved region in the E2 gene and a variable region in the nsP3 gene. The sequences revealed that the strain from Poland belonged to subtype SAV 2, indicating a very strong genetic identity with isolates from Italy and France.
Koi herpesvirus (KHV) has infected farmed common carp in Poland clinically and asymptomatically since 2004. The role of non-carp species as vectors of virus transmission is well known except for in the case of KHV. The aim was to better understand this virus’ infection and transmission pathways in common carp, looking at the potential vector role of fishes kept with them.
Material and Methods
Eight species were experimentally infected with KHV by immersion in a suspension at 20°C ±1 and transferred to a tank after 45 minutes. Specimens were euthanised at intervals up to 56 days post infection (dpi) and tissue was examined for KHV DNA. Surviving infected fishes were introduced at intervals, each time into a separate tank, to naïve common carp for experimental infection. These were observed daily for symptoms, sacrificed along with controls after three months, and dissected to provide tissue samples. Also fish from 14 species collected from a farm with a history of KHV were sampled from 3 to 22 months after disease was confirmed. Organ sections from single fish were collected in a single tube.
Viral DNA was detected in tench and roach samples up to 49 dpi, but in three-spined stickleback and stone maroko samples only up to 14 dpi. Transmission of KHV to naïve carp occurred after cohabitation. KHV DNA was detected in three fish species three months after the farm outbreak.
We confirmed that grass and Prussian carp, tench, roach, and brown bullhead can transfer the virus to naïve common carp.