Lymphocystis Disease of Fishes, by Dr. Adrian Lawler

Lymphocystis Disease of Fishes

Adrian Lawler, Ph.D.
(retired) Aquarium Supervisor (l984-l998) J. L. Scott Aquarium Biloxi, Ms 39530
Original to Aquarticles

Description
Lymphocystis is an infectious viral disease of freshwater and saltwater fishes that causes cell enlargement (many more times than normal cell size), also called hypertrophy, usually on the skin and fins. The enlarged cell nodules may each reach 0.3 mm to greater than 2.0 mm in diameter, each becoming a virus factory. Lymphocystis is the most common viral infection of aquarium fish, and has been reported in over 125 species of freshwater and marine fishes.

The disease usually runs its course in 4 or more weeks (depending on species involved, water temperature, and other variables) and then the enlarged cells rupture or slough off and release the viral particles into the water. 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. I have worked with many thousands of fishes of various freshwater and salt water species and do not recall a single death being directly due to a lymphocystis infection.

After lymphocystis lesions are lost, the host tissue heals up. Adhesions and scarring can occur during healing. If the gills are affected, the fish can have difficulty breathing, especially if gill surface areas are destroyed (no longer present), or adhesions or scarring occur and gill surfaces are thus reduced in surface area or functional quality for oxygen uptake.

The viral particles in the water can go on to infect another fish of the same or closely related species. I suspect the virus can also become dormant and remain viable in sediments for years. The virus may be stored for years (for future research) by either freezing or freeze-drying the separated viral particles, infected tissues, or infected whole fish.

The disease poses no known health hazard to humans. To decrease spreading this disease to other fishes, infected fish should be buried or burned, and not thrown back into the water.

The viral agent of lymphocystis disease is an iridovirus (of the family Iridoviridae) called Lymphocystivirus (genus name). Iridoviruses range from 120-300 nm (nanometer = one billionth of a meter) in diameter. Iridoviruses have an icosohedral or 20-sided shape, and a DNA core.

I have worked on the disease in silver perch (Bairdiella chrysura), white-tailed damselfish (Dascyllus aruanus), black-tailed humbug (Dascyllus melanurus), copper banded angelfish (Chelmon rostratus), Koran angelfish (Pomacanthus semicirculatus), Moorish idol (Zanclus canescens), foureye butterflyfish (Chaetodon capistratus), orbiculate bat fish (Platax orbicularis), queen angelfish (Holacanthus ciliaris), and warmouth or goggle-eye (Lepomis gulosus).

LymphoWarmouthBig.jpg (114993 bytes)

Infection
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).

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."

Lymphocystis, once acquired, must run its course. There are some ways to decrease the chance of fish getting the disease:
…Handle fish carefully to reduce injury to skin and fins and slime coat.
…Reduce or prevent stress on the fish. Stress would include overcrowding, starvation, overfeeding, sudden environmental changes (temperature, salinity, pH, DO, strong currents carrying debris, etc), toxins (pesticides used nearby; high ammonia, nitrite, or nitrate), or anything else that could affect the immune system or cause physical injury. Lymphocystis frequently appears on the tail due to nipping by other fish, usually a result from overcrowding.

While I was working on this disease in silver perch, I suddenly had numerous warts appear on my hands. I handled many experimentally infected fish. I could get no doctor to excise a wart and compare the wart virus with the lymphocystis virus I was working on, so I leave the answer to this question to those in the future. Several months later, shortly after I worked in concrete (a basic pH medium) building a concrete pond, the warts just as mysteriously disappeared, and remain gone over 30 years later.

Did I find that lymphocystis can infect humans? And that warts can be cured by abrasion and/or a basic solution? Only the future work of others will tell.

References
Dukes, T. W., and A. R. Lawler. 1975. The ocular lesions of naturally occurring lymphocystis in fish. Canadian Journal of Comparative Medicine, 39 (4): 406-410.

Howse, H. D., A. R. Lawler, W. E. Hawkins, and C. A. Foster. 1977. Ultrastructure of lymphocystis in the heart of the silver perch, Bairdiella chrysura (Lacepede), including observations on normal heart structure. Gulf Research Reports, 6 (1): 39-57.

Lawler, A. R., H. D. Howse, and D. W. Cook. 1974. Silver perch, Bairdiella chrysura: New host for lymphocystis. Copeia, 1974 (1): 266-269.

Lawler, A. R., J. T. Ogle, and C. Donnes. 1977. Dascyllus spp: New hosts for lymphocystis, and a list of recent hosts. Journal of Wildlife Diseases 13 (July, 1977): 307-312.

Lawler, A. R., J. T. Ogle, and C. Donnes. 1978. New hosts for lymphocystis. Gulf Research Reports 6 (2): 183-184.