Ich (which causes "white spot disease") is a ciliated protozoan parasite that bores into the skin and gills of fish where it feeds, destroying tissue and thereby blocking exchange of oxygen and carbon dioxide, usually leading to death of the host. Each parasite grows on the fish from roughly 40 microns, which cannot be seen by the naked eye, to approximately one millimeter in diameter, which can easily be seen as a white spot. The parasites leave the fish in about 5-6 days (a ciliate with its typical large nucleus is shown in the image). Each cell then divides multiple times to produce up to 1000 more infective organisms. The entire life cycle takes about 6-7 days. With subsequent rounds of infection the number of parasites continues to increase, and each wave of re-infection becomes more deadly than the last. By the second or third re-infection the fish population is usually overwhelmed and fish begin to die. Fish that survive mild infections can develop immunity.
There are currently no drugs or chemicals that kill Ich while it resides in the fish skin or gills; they can only kill Ich when the parasite is in the water, and therefore all current therapies require a cyclical re-treatment program.
The first major outbreak of Ich in North America was recorded in 1898 at the Chicago World Fair. Ich is a well-known problem for aqua-culturists, aquarium owners, pond owners, hobbyists and retailers of freshwater fish. People and birds can also carry the parasite, unknowingly, from pond to pond.
"Work to sequence the genome of this parasitic protozoan unexpectedly revealed that bacterial DNA sequences were also present," noted Craig Findly, one of the College's researchers on the project. "Following up this discovery led to our demonstration that two new species of intracellular bacteria use Ich as their host. We now need to determine if these intracellular ba
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University of Georgia