Discovery Could Lead To New Treatment Options For ‘Ich’ In Freshwater Fish, Scientists Say

A new discovery of “Ich” has given scientists hope of finding new ways of treating the fish infected with the parasite.

Ich intracellular bacteria

© 2009 The UGA College of Veterinary Medicine

A team of researchers reported on Dec.3 that they have discovered the presence of two bacteria in Ichthyophthirius multifiliis, or “Ich,” a single-celled parasite that commonly attacks freshwater fish. They hope the discovery could open up new avenues for treating fish infected with the parasite.

The discovery was made during an Ich genome mapping project conducted by five researchers from The University of Georgia College of Veterinary Medicine, two researchers from Cornell University College of Veterinary Medicine and one researcher from the J. Craig Venter Institute. While working to sequence the genome, they found that the parasite harbors two apparently symbiotic intracellular bacteria: Bacteroides and Rickettsia. The scientists say the two bacteria represent new species.

“It was unexpected; it was stunning to find bacteria in Ich.  And, it came about due to the genome sequencing,” said Harry Dickerson, a co-author of the study, which is published in the December issue of Applied and Environmental Microbiology.

Now, the scientists plan to determine if Ich remains infective if the bacteria are removed. They say it could bring them a step closer to developing better treatment for Ich, also known as white spot disease.

Ich bores into the skin and gills of fish where it destroys tissue, thus blocking the exchange of oxygen and carbon dioxide and leading to the fish’s death. There are currently no drugs or chemicals that kill Ich while it inhabits the fish, according to the University of Georgia. It can only be killed when the parasite is in the water. Therefore, all current therapies require a cyclic re-treatment program.

“Ich occurs world-wide and is one of the most common protozoon pathogens of freshwater fish,” Dickerson said. “It is easily recognized by most aquarists, and fish farmers often are confronted with massive epizootic outbreaks to devastating economic effect.”

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