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Interesting new research about Ich (whitespot disease)


Jennifer

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I was reading this in a journal today and thought I would share it in case some of you might be interested.

Georgia veterinary college leads that way in discovery of freshwater fish parasite

Dec 16, 2009 Athens, Ga. -- Through whole-genome sequencing, researchers at the University of Georgia College of Veterinary Medicine have uncovered new information about treating “Ich,” a single-celled protozoan parasite that attacks freshwater fish.

Researchers found that Ich (Ichthyophithirius multifiliis) contains two “apparently symbiotic intracellular bacteria” that represent a new species, according to the college.

It was the presence of Rickettsia, one of the two bacteria, DNA sequences in the initial genome data that showed gave scientists the indication that bacteria might live in side the Ich.

“Intracellular bacteria have been described in free-living ciliates such as Paramecium, but never in Ich, which is an obligate parasite,” the college says.

“It was unexpected; it was stunning to find bacteria in Ich,” says Harry Dickerson, who has been studying Ich in the veterinary college for more than 20 years and co-authored the study.

Ich, the cause of “white spot disease,” bores into the skin and gills of fish, where it eventually destroys tissue and kills its host by blocking the exchange of oxygen and carbon dioxide. There are no drugs to kill Ich in fish, only in the water. The new discovery will lead researchers to try and determine what role the two bacteria play in the physiology of Ich and whether Ich remains infective if the bacteria are removed, the college says. The results of that research could lead to new treatments of Ich.

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Am I correct in thinking that rickettsia are present in the gut of insects and assist in the digestion of cellulose? If so I wonder What they are doing in a whitespot.

I think rickettsia are usually pathogenic intracellular bacteria (unlike a lot of bacteria they cannot survive outside a host). Rickettsia are quite commonly transmitted by ticks (which is why a lot of ticks transmit disease caused by the rickettsia). I don't think the rickettsia typically have any benefit to the host - I think the relationship is mostly parasitic - which makes this case particularly unusual. I do wonder if there could be an underlying disease that the rickettsia would be causing - in fact, maybe the rickettsia is the organism that causes some of the disease symptoms...

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