What is Lymphocystis?
Lymphocystis is a chronic disease of freshwater and marine fishes caused by infection with an iridovirus known as Lymphocystivirus or Lymphocystis disease virus (LCDV), which is a member of the family Iridoviridae. The infection causes cells to become megaloblastic, thus forming small tumors (bumps or growths), often along the lateral line or the pedicle,where the fin meets the body. The tumors sometimes take on the appearance of tiny cauliflowers, thus the name. Although the disease has been seen worldwide in salmon and trout farms and in numerous species since its first description in 1874, its viral cause was not identified until late 1962. The lymphocystis viruses are considered much less pathogenic (disease-causing) than their iridoviral relatives, the ranaviruses and megalocytiviruses, which can cause severe, systemic disease with higher moralities. An interesting point is that LCDV is potentially heterogenous, containing sequences from a number of different variant viruses read more here https://www.ncbi.nlm.nih.gov/pmc/articles/PMC421667/. Some genome sequenced iridoviruses showed LCDV- C, LCDV-1, CIV, ISKNV, TFV, ATVall in the same sample.
Although lymphocystis disease normally does not cause significant moralities, it does cause unsightly growths on fish that reduce their marketability, and in some cases, severely infected fish may die.
Is my betta susceptible?
The short answer is yes,your betta is susceptible. Lymphocystis disease has been reported in over 125 different marine and freshwater fish species from 34 different families. It affects evolutionary- advanced orders of bony fishes (teleosts), including cichlids (Cichlidae), killifishes (Cyprinodontidae), gouramies (Osphronemidae), sunfishes (Centrarchidae), gobies (Gobiidae), butterflyfishes (Chaetodontidae), damselfish/clownfish (Pomacentridae), dottybacks (Pseudochromidae), snook(Centropomidae), drum (Sciaenidae), sea basses (Serranidae), and many others.
A very interesting point is that Lymphocystis does not affect wild bettas and does not affect less advanced orders, including catfish (Order Siluriformes), cyprinids (such asgoldfish, koi, barbs, or danios; Family Cyprinidae) or salmonids (Family Salmonidae).
What are typical signs of disease?
The most obvious sign is the appearance of small to moderate-sized, irregular, nodular, wart-like growths on the fins, skin, or gills that some say look like cauliflower. These may be cream- to gray-colored but can be other colors if they appear under pigmented areas. These may appear over the course of days and may last for weeks.
Pop-eye (exophthalmia; marked protrusion of the eye) has also been seen and results from lymphocystis masses in or behind the eye in bettas pushing the eyeball out.
Fish with Lymphocystis normally do not behave any differently from uninfected fish in the same group. However, if there are large numbers of nodules on the body or fins, or if they are covering a large portion of the gills, these may alter swimming or breathing patterns.It would be at this point you would need to consider euthanasia.
What are these nodules I am seeing?
What you are actually seeing is clustered groups of greatly enlarged, infected cells known as fibroblasts, which are part of the connective tissues in the betta fish. These infected cells are 50,000–100,000 x larger in volume than normal cells because they have become “virus factories,” using the infected cell’s machinery to create the defective copies to produce more virus, and thus are filled with virus particles. After these “virus factory cells” have completed their production of virus particles, the cells will burst and shed virus into the surrounding environment in order to live on.
Most normal fibroblasts are approximately one hundredth of a millimeter (0.01 mm) in diameter. The individual infected cells,on the other hand, can be from one tenth of a millimeter—0.1 mm—to over well over 2 mm. Every single infected cell is surrounded by a thick membrane. Fibroblasts are composed of simple connective tissue cells normally found throughout the fish’s body, and so Lymphocystis nodules may be seen internally as well as externally forming a lump before exiting the skin. However,fibroblasts are most often seen in the skin, fins, or gills and seem to be the more commonly affected areas on bettas.
How do I tell if my betta has lymphocystis and not hyperplasia?
Well this is a good question because in addition to seeing the wart-like growths on the fins, skin,or gills, a wet mount (fresh) slide biopsy of these growths (careful removal of one of these growths from the skin, fins, or gills) should be examined under the microscope. A strong tentative diagnosis of Lymphocystis can be made based on seeing round to oval, grape, or balloon like structures, often in clumps. Fish may also be infected with Lymphocystis without having obvious lesions that are visible with the naked eye. These fish may have smaller infected cells or may have one or more internal organs infected (e.g., inside the eye, spleen, or other organs). Lymphocystis, in these cases, may only be seen after microscopic examination of a wet mount (fresh) biopsy of suspected infected tissues, or by using more advanced techniques such as histopathology, electron microscopy, or molecular methods.
Hyperplasia (increase in cell number) can be confused for lymphocystis (increase in cell size), and various bacterial or fungal infections. Lymphocystis usually appears whitish in color, and distinct clusters of enlarged cells can be easily seen which have a visibly enlarged blood supply system supporting the rapidly expanding lymphocystis cells. Sometimes lymphocystis infected areas appear to have reddish-colored areas, which are from the enlarged blood system. The descriptive term for lymphocystis is hypertrophy, or increase in individual cell size.
Hyperplasia is usually the same color as the surrounding cells as it is an extension or new growth (just new cells growing outward) of those cells, and there is no noticed cell enlargement. If the hyperplasia arises from unpigmented cell tissue, then that hyperplastic growth will be white, or non-pigmented. In cases where lymphocystis and hyperplasia are found on the same fish, hyperplastic tissue(if occurring later) can grow over the already established lymphocystis tissue,then giving the same external color to the lymphocystis area as the tissue from which the hyperplasia originated, and thus giving an abnormal false color appearance to the original lymphocystis infection.
For an accurate diagnosis, work with a fish health professional or fish disease diagnostic laboratory if you suspect your fish have lymphocystis.
Can lymphocystis be confused with any other diseases?
Yes. In early stages of the disease, the nodules may be relatively small and may be confused with the parasites Ichthyophthirius multifiliis(Ich, freshwater white spotdisease), Cryptocaryon irritans (marine white spot disease),digenean trematodes (“grubs”), or heavy infection with Epistylis (astalked, ciliated, protistan parasite). Lymphocystis nodules may also be confused with epitheliocystis (an intracellular bacterial disease), clumps of fungus, or mucus tags. Some skin neoplasias (cancers) may also be confused with lymphocystis and Hyperplasia can also be had to distinguish from Lympocystis.
Because of the potential confusion with other disease agents, diagnosis of lymphocystis should be accomplished by a qualified fish health professional to rule out these other potential causes.
What factors contribute to development and spread of lymphocystis disease?
Lymphocystis is spread by fish-to-fish contact or contact with infected tissues. External trauma from spawning, aggression, parasites, or handling can facilitate infection and spread. In addition, crowding, shipping, and other stressors appear to trigger disease outbreaks. Lymphocystis does not appear to be spread by vertical transmission (i.e., from parents to offspring via infection of eggs or sperm in bettas). But if the male has it and is left to care for the fry it can be passed easily.
Although all the contributing factors are not known well known in bettas, there do appear to be different genetic variants or possibly “species” of Lymphocystivirus. Each of these affects a different group of fish. Because the virus that causes lymphocystis has been difficult to work with, experts have only officially assigned one Lymphocysti virus species, Lymphocystis disease virus 1 (LCDV-1 from Asia). Several other variants have been suggested and may be determined to be separate species (including LCDV-2, LCDV-C), but these have not yet been officially accepted by all virus expert sand some have suggested that it is also a heterogeneous virus containing sequences from a number of different variant viruses.
Based on clinical observations of mixed species groups and other anecdotal evidence, there may be additional strain variations and/or differences in individual fish species sensitivity to infection. In mixed natural or aquarium populations of fish,typically only one or two species will be infected. However, in experimental settings, multiple species can be infected by direct exposure to infected tissues. Although we were not able to infect wild bettas.
What happens to infected fish?
Lymphocystis is usually self-limiting disease, meaning that, in some cases, the lesions will clear up after a few weeks or months in most warm water fish species and the fish could be sold or bred adding to the issues of controlling this virus in bettas. However, because of the unsightly growths, fish normally cannot be sold during this time. Betta mills are one of the main causes of the spread of this virusin bettas. If a fish has numerous lesions and/or lymphocystis nodules cover a large portion of important organs (e.g., the gills), there may be some impairment and greater chance of secondary infections by bacteria, parasites,or fungi that can now more easily infect the fish and help contribute to moralities.
Can fish with lymphocystis be treated?
Currently, there is no good treatment that will speed up recovery from this disease. Most often, the disease must run its course in an affected fish. Fortunately, most cases of lymphocystis in warm water fish will resolve on their own after some time, as long as husbandry is good (good water quality/chemistry, good nutrition,correct population densities, optimal social groups) and as long as other stressors have been eliminated. Although it is not an ideal solution, at present, the best option is removing the fish from your line and any contact with other fish.
Because lymphocystis disease in bettas tends to develop in parts of tissues that are less exposed to the immune system (e.g., at the periphery, away from blood vessels that carry immune cells) and in tissues with a thick hyaline membrane that may”hide” these cells, an immune response normally does not develop until after cells have burst and released virus. There is some evidence that fish infected with lymphocystis will develop less pronounced lesions if they are re-infected or if lesions recur.
Culling (removing) infected fish from a population may help reduce overall loads of virus in the system as well as infection rate for farms or breeders, but it is difficult to cull all affected fish because some infections may not be visible with the naked eye,and many less severely infected fish may remain in the population to potentially infect other fish. Culling, therefore, may not be as effective a measure for aquaculture populations as for hobbyists or display aquarium. Culled fish can be isolated until their lesions resolve, but lesions may recur. If they do, they will most likely be less severe.
What can I do to prevent or reduce the likelihood of lymphocystis infection in my betta population?
Quarantining all new fish coming into your facility for at least 3-4 weeks and daily observation of these fish during this time will help alert you to any potential outbreaks of lymphocystis caused by shipping or acclimation stressors, and will also help increase the fish’s immunity. A full round of anti-parasite and bacteria and fungus meds should also be used during this time. Removal and/or isolation of affected fish may help reduce spread or severity. However, it is likely that other fish in the group are also infected, so removal and/or isolation of grossly affected fish will help reduce the number of active”shedders” and carriers of the virus.
As with other diseases,making sure water quality and your husbandry practices as a whole are optimal,being careful with handling, avoiding overcrowding, and reducing or eliminating unnecessary stress (including parasites) that may result in physical trauma will all help reduce the potential for infection and spread.
Use clean water (a protected water source that has not been exposed to the virus or other potential disease-causing organisms): if your water source contains other fish with lymphocystis, this will increase your risk as well.
Be sure to check your own fish carefully and work with a fish health professional if you suspect you may have a lymphocystis outbreak or the fish population has a history of the disease. Remember that cyprinids (members of the carp family, including goldfish, koi, barbs, rasboras, danios, and rainbow and redtail black sharks),catfishes, and salmonids do not get lymphocystis but they do get herpes or carp pox.
Look for small to medium-sized nodules or warts on the fins, skin, or gills of your fish.Although other organs may be infected, growths on the fins, skin, and gills are more common. Because lymphocystis lesions may not always be visible to the naked eye, fish tissues may still need to be examined microscopically. Biopsies of the skin, fins, and gills, especially from areas that appear to have some subtle abnormalities, should be examined under the microscope for evidence of enlarged cells typical of lymphocystis (see Figures 3 and 4). If any nodules are seen, these should be biopsied and examined.
How to disinfect equipment after handling fish with lymphocystis?
Experimental studies have shown that iridoviruses can be inactivated with any of the following compounds, after 15 minutes at 77°F (25°C): potassium permanganate (100 mg/L or higher), formalin (2000 mg/L or higher), or sodium hypochlorite (liquid bleach—various formulations) at 200 mg/L or higher. Be sure to use proper precautions (adequate ventilation and personal protective equipment, e.g.,gloves, goggles, respirator) when handling these chemicals. In addition, iridoviruses may also be inactivated by raising the pH to 11 or greater for a minimum of 30 minutes or with high temperatures (122°F [50°C] or greater for 30 min).
References and Recommended Reading
Noga, E. J. 2010. Problem 40. Lymphocystis. In Fish disease: diagnosis and treatment. 2nd edition. Wiley-Blackwell. Ames, Iowa. Pp. 171–173.
Wolf, K. 1988. Chapter 22. Lymphocystis disease. In Fish Viruses and Fish Viral Diseases. Cornell University Press. Ithaca, NY. Pp. 268–291.
ICTV (International Committee on Taxonomy of Viruses) online.
J Virol. 2004 Jul; 78(13): 6982–6994.