Carp Pox is not a parasite, it is a herpes virus but NOT the deadly KHV virus. Carp pox usually worsens in the winter and can resolve when water temps rise. There is no cure and is not harmful to the fish unless it affects eating or gill movement.
The Carp pox virus is very common and the lesions come and go according to water parameters- similar to cold sores in humans. Once a fish has the carp pox virus they will always have it, even if the fish does not show any signs of the lesions.
The carp pox virus will take advantage of a fish with a weaken immune system. Especially in the winter and spring when the fish’s immune system is at its lowest.
Some fish can show no signs of lesions (carp pox) but can still be carriers. Unless the fish shows the lesions you never know if the fish you buy have the carp pox virus. Carp pox is mildly contagious.
Carp pox cannot live without a host, within 24 hours after the ALL fish are removed from the pond the carp pox is gone. A fish less pond cannot support the carp pox virus.