Treatment breakthrough for guppy disease

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Scientists have identified a potential treatment for guppy disease - a condition which has significantly affected the ease of keeping this popular tropical freshwater aquarium fish.

Guppy disease, which is caused by a systemic infection of the protozoan parasite Tetrahymena, has become a serious global problem and has proved so difficult to treat that  some shops have switched fish suppliers or even stop selling the fish.

Now scientists from the The French Associates Institute for Agriculture and Biotechnology of Drylands at The Jacob Blaustein Institutes for Desert Research in Ben-Gurion University of the Negev, Israel, have come a step closer to developing a treatment for the disease.

Their findings, which are due to be published in the Journal of Fish Biology, show how they tested a number of orally administered chemicals fed to guppies and monitored the survival rate of Tetrahymena parasites exposed to the chemicals themselves.

The most effective chemicals added to the water were niclosamide, albendazole and chloraquine, which resulted in parasite survival rates of 23%, 35% and 60% respectively following two-hours exposure at 100ppm, with longer exposure rates killing more parasites.

Feeding guppies a diet containing the chemicals also killed off some of their parasites. The authors wrote: "Mortality rates were significantly lower in all treatment groups; in trial I, 30% and 33% mortality in 5 and 40 mg kg(-1) niclosamide-fed fish vs. 59% mortality in controls; in trial II, 35%, 13% and 10% in 50, 100 and 200 mg kg(-1) niclosamide-fed fish vs. 64% in controls.

"The effect of the cysteine protease inhibitor E64 was tested in tissue culture, by measuring histolytic activity of the parasite (Tet-NI) on a guppy-fin cell line, based on cell depletion.

"Tet-NI feeding activity was significantly reduced following pretreatment with E-64 relative to non-treated Tet-NI. E-64-pretreated Tet-NI was injected i.p. into guppies: recorded mortality rates were significantly lower (35%) than that in non-treated Tet-NI (60%), suggesting inhibition of the parasite's cysteine protease as a possible therapeutic approach."

For more information see the paper: Leibowitz MP, Chettri JK, Ofir R, Zilberg D. (2010) - Treatment development for systemic Tetrahymena sp. infection in guppies, Poecilia reticulata Peters. J Fish Dis. 2010 Mar 8. .