Symptoms: While infected, the fish may become slowed or weakened, or more visible, and thus be more prone to predation or attack. If there are mouth lesions, the fish may have difficulty in feeding or may not be able to feed. The low mortality rate some attribute to lymphocystis is mostly due to secondary bacterial or fungal infections
Causes: Lymphocystis does show some host-specificity, i.e., each strain (or species) of lymphocystis can infect only its primary host fish, or some additional closely related, fish.
DNA studies have showed that there are different species of the virus. This has been suspected for some time because the viral particles from different fishes vary in size plus the virus from a fish usually will infect only that species of fish or a few other species closely related to the primary host.
The virus enters through broken skin or injured tissue (usually skin or fin). If the virus gets into the blood (usually via gill infections) then various internal organs can be infected. In l974 I showed that the spleen, tissues behind the eye, eye, and many other internal organs can be infected via systemic infection. One can easily infect fish by putting them into a bucket of water, introducing the virus, then injuring fish by vigorously swirling a stiff bottle brush in the bucket. One can also run a sharp probe on the skin or tail (see warmouth picture below) and expose the fish to the virus to infect them.
Incubation times (until lesions are visible to eye) range from about 10 days at 25 C to longer, depending on species involved, temperature, and other variables.
Important or valuable affected fish should be isolated and monitored for secondary bacterial or fungal infections that should be treated with appropriate drugs.
In 1979 I discovered that goggle-eye (warmouth), when subjected to heavy rains and sediment loads, came down with lymphocystis. It is unknown, in this case, whether stress or physical injury led to the lymphocystis infections. Stress to the fish, in this case, could be from exposure to sediments in the water leading to breathing problems, from getting tired trying to maintain their position in the swift water, from being exposed to toxins swept in by the water, etc. There is also the possibility that sediment or debris particles hitting the fish in the swiftly moving water caused injury that led to the infections (similar to injuring fish in a bucket by swirling a brush).
Treatment:
Control There is no way to cure a viral disease in any organism yet, no matter what some of the fish medications claim. Some virus diseases in various organisms can be prevented by vaccination, or slowed down by medications. There is no vaccine for lymphocystis yet.
Some medications claim to cure lymphocystis in several days to a week. However, depending on the stage of the disease, many enlarged cells will burst and disappear on their own (without using the "cure"), making some think their chemical has cured the disease. One can also excise the enlarged cells, affecting an apparent "cure," but, in reality, just removing most of the infected cells (which then can no longer be seen). Lymphocystis cannot be "cured."
