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I originally posted this about two years ago in response to Bruce Moomaw's woes with respect to Neon Tetra Disease and Whirling Disease in Characins. While the original TFH article quoted below may be in some respects out of date, I have yet to see any updated information that conflicts with what will appear below. In the light of Malaikah's recent bad experiences with a Diamond Tetra, I'll repost the original in full below, including my brief intro written for Bruce.


Bruce, I found the issue of TFH in question again - March 1977. Article entitled Incurable Microsporidian Diseases, pp 45-48, by Dr Mark P. Dulin. In case you can't get hold of the issue, I'll reproduce the article below.

Incurable Micrisporidian Diseases

Just as there are still many human diseases which cannot be successfully treated, there are a variety of incurable fish diseases. Some of these diseases remain sub-clinical, and infected fish lead a relatively normal life, while others can be very severe and even fatal. One group of protozoan parasites, the microsporidia, is the subject of this month's column. I thought this might be an appropriate time to discuss this group, since the parrotfish involved in last month's column was affected with a microsporidian disease. (Post-Mortem Examination by Dr Mark. P. Dulin, February 1977, pp 52-57).

Diseases caused by these obligate intracellular parasites are more common than you might think. Microsporidians also infect more than fishes alone: they have also been reported in invertebrates, reptiles, amphibians and birds.

Most aquarists have probably heard of the so-called "Neon Tetra Disease", this is a microsporidian disease caused by Plistophora hyphessobryconis. This parasite has apparent histolytic capabilities which can cause extensive disintegration of the muscles [1], not only in tetras but also in many other fishes as well. Characins affected with this disease develop whitish areas which shine through the skin. Later in the course of the disease there is a complete discolouration of the normal skin pigmentation. Other signs of this disease include spinal curvature, equilibrium dysfunction, loss of weight, muscular paralysis, bizarre swimming behaviour and fin degeneration. Some of these signs of disease can also occur in other chronic diseases sich as piscine tuberculosis, so care must be taken to avoid a mis-diagnosis.

Other species of Plistophora can have equally devastating effects on a variety of freshwater and marine fishes, but some species produce effects so minor that they go undetected. A more benign microsporidian is Plisotphora ovariae. Although it can cause considerable damage to the gonadal tissue of Golden Shiners, visible manifestations of the disease in living fish are usually not apparent. Considerable evidence suggests that this parasite is passed from one generation to another via infected eggs [2], making effective control rather difficult.

Some of the other common microsporidians are in the genus Nosema (syn. Glugea). Various species have caused extensive damage to abdominal organs, viscera, musculature, gills and even the brain of both marine and freshwater fishes. The clinical signs of disease may vary upon the particular tissues under attack. If death does occur (and it often does) it is a result of either organ dysfunction or secondary bacterial and fungal invasions.

Life Cycle

The generalised microsporidian life cycle is assumed to be as follows: spores are ingested either as they are released from infected fishes or as infected tissues are eaten. Once a spore reaches the gut, the polar filament is extruded to presumably anchor the spore while the sporoplasm penetrates the intestinal mucosa. After the sporoplasm enters the circulatory system it is carried to suitable tissues for further development. After the infective unit enters a host cell, asexual reproduction (schizogony) then takes place. During this division, autoinfection may further spread the parasite through the host. Sexual reproduction (sporogony) eventually occurs, producing the cysts or destroyed musculature by which the disease is often recognised. Mature spores are released to the outside, allowing water to act as a vehicle for fish-to-fish transmission.

Diagnosis

Although a tentative diagnosis can often be made upon the appearance of grossly visible lesions, a microscopic examination of affected tissues is required for a definitive diagnosis. Spore-filled pansporoblasts can be readily seen on both tissue imprints and stained tissue sections. The genera are separated based upon the number of spores produced in each sporont. For example, Nosema have two while Plistophora produce sixteen or more.

Control

Because infected fishes serve as a reservoir of infection to other fishes, they should be removed from the exhibtion aquarium. It then becomes a judgement decision whether these fishes should be destroyed or given a chance to recover. Mildly infected aquarium fishes may survive some of the microsporidian diseases without apparent discomfort, while other diseases must certainly be excruciatingly painful. If affected fishes are havily infected and are suffering, they should be destroyed. Do not flush the dead fishes down the toilet or grind them in a garbage disposal - this could lead to contamination of natural waterways. Infected fishes should either be burned or buried away from water drainages.

Because there is no cure for any of these microsporidian diseases, about the best an aquarist can do is to be able to recognise them for what they are and take steps to prevent other fishes from contracting the disease. Should an epizootic occur i your aquarium, completely disinfect the tank with a household bleach (Chlorox or its equivalent) before restocking it with healthy fishes. Signs of the developing disease may not be present at the time of purchase and during quarantine: therefore, the introduction of microsporidian-infected fishes is a definite possibility. You can reduce the likelihood of mocrisporidian problems by providing your fishes with optimal living conditions and being careful not to feed them infected tissues from diseased fishes.

References

1. Rogers. W.A. & J.L. Gaines, 1975, "Lesions of Protozoan Diseases In Fish", pg.130, in The Pathology Of Fishes, ed. W.E. Ribelin & G. Migaki, University of Wisconsin Press, Madison, Wis.

2. Summerfelt, R.C. & M.C. Warner, 1970, "Incidence and Intensity of Plistophora ovariae, a Microsporidian Parasite of the Golden Shiner Notemigonus chrysoleucas", pp. 142-160, in A Symposium on Diseases of Fishes and Shellfishes, ed. S.F. Snieszko, American Fish Society Specialist Publication No. 5, Wash. D.C.

An additional note of my own - the photographs illustrate both NTD and Nosema. One of these photographs shows lesions that look like White Spot, but which are more regular in size, larger and fewer in number (exact identity not given, but presumably Nosema). Comparison of this photograph with a photograph from the January 1977 issue of TFH (Ich by Dr Mark. P. Dulin, January 1977, pp 57-60) is instructive - this latter photograph shows a Stickleback infected with Ich, and the difference in the appearance of the lesions is readily apparent.. The other photographs show the more familiar whitish tissue disintegration (including a classic illustration of severe Plistophora in the Neon Tetra, an excellent illustration which I have yet to see bettered in any other source text).

Another article of interest concerns the Japanese Fish Hospital (TFH, May 1975, pp 19-29, with B&W illustrations). This is the hospital attached to the Toba Municipal Aquarium in Toba City, Mie Prefecture, Central Japan. It might be interesting to perform a Google search to find out more about this institution, and see if similar institutions have arisen elsewhere since the article was published. They may be able to answer enquiries about the microsporidians cited in the above 1977 article, as it is reasonable to assume that such organisms are a focus for research by the staff.

While I have been fortunate and never encountered microsporidians myself, and note the difficulties encountered by others with respect to these insidious parasites, some thoughts have crossed my mind. While Methylene Blue is an effective protozoicide against White Spot, it seems to be discounted as an effective treatment for microsporidians, presumably because the freely motile infective agents of the latter are encysted. Likewise, Metronidazole (a treatment for Hexamita, the cause of Hole In The Head Disease) seems to have received little or no mention as a possibility for treating microsporidians (although the May 1977 issue of TFH, pg 60, covers its success against Hexamita in some detail). An unrelated article (April 1977, pp 60-64, on Camallanus worms) mentions an organophosphorus compound called Trichlorfon which might prove interesting to try in experiments against microsporidia too, although like ALL organophosphorus compounds, it is VERY toxic (including to Man) - remember that organophosphorus compounds include chemical weapons such as Sarin! However, since trichlorfon was developed as an insecticide, its use against microsporidia would probably be a desperate last resort, and very much in the realms of "well, the fish will die anyway if I do nothing ...".

Finally, on a more up to date note, I have a bottle of "Protozin" among my fish medications, which contains within the blurb on the packet a claim that it is a treatment for NTD. "Protozin" is made by the same company that makes the more familiar "Cuprazin" and "Myxazin" used in marine aquaria. The accompanying literature says "PROTOZIN is used for the control of all protozoan and fungal infections e.g., Whitespot, Fungus, Neon Tetra Disease, Velvet, Costiasis and Trichodoniasis. Do not use when Mormyrids (e.g. Elephant Nose) or Rays are present. For fresh water usage only". If anyone has had ANY success using this, then this will be a VERY welcome development, not least for Bruce, who has apparently experienced complete wipeouts because of NTD!



Last edited by Calilasseia at 03-Mar-2005 00:15

Panda Catfish fan and keeper/breeder since Christmas 2002