The optimal temperature for viral propagation in KF-1 cells is 15–25 C; at
30 Cthese cells do not produce virus [26]. The virus induces
typical plaques in 3–4 days after inoculation in the cultured
cells along with the formation of syncytia and increase in
cytoplasmic vacuoles. Later, the cells become round and
detach from the substrate [65]. KHV infected cells with
deformed morphology can be converted to normal following
shifting up of the temperature and can again deform after
transfer to the permissive temperature. This is because viral
propagation and viral gene transcription is turned on and off
by shifting cells to the permissive and non-permissive temperatures.
This suggests that virions persist for long periods
in the fish body, enabling a new burst of infection upon a shift
to a permissive temperature [18].