The myxosporean parasite, Myxobolus cerebralis, affects salmonoid fishes such as trout and salmon. This parasite causes a whirling disease in farmed trout and salmon, as well as in wild fish populations. It was first scientifically described from a rainbow trout specimen from Germany over 100 years ago, but this has unfortunately spread around the world to other places in Europe, North America, South Africa, and more.
During the 1980’s, researchers found that the Myxobolus cerebralis required a segmented worm called a tubificid oligochaete in order to complete its life cycle. This parasite basically infects the host fish with its cell by piercing them with polar filaments which is ejected from their nematocyst-like capsules.
The effect of this whirling disease mainly affects juvenile fish like fry and fingerlings. This is because it results in a deformed skeleton and also causes neurological damage. It is evident that a fish has whirling disease because the fish will whirl forwards in an awkward corkscrew-like pattern instead of how fish normally swim. They will also find feeding difficult and are more vulnerable to predators. The mortality rate is high for fingerlings. Those who do survive the whirling disease will be deformed as Myxobolus cerebralis will reside in their bones and cartilage. This is because the cartilage and bones will act like a reservoir which is released into the water after the fish has died. As a result, it is one of the most economically important myxozoans in fish and one of the most pathogenic. Fortunately, this parasite is not transmissible to humans.
Biologists are currently working out how to disarm the triactinomyxon spores by making them fire prematurely. Lab results have found that extreme basicity, acidity, electrical currents, and a moderate to high salt concentration will allow them to discharge prematurely. However, trout mucous, cnidaran chemosensitizers, and neurochemicals are fairly ineffective. It is unclear whether any of these methods would translate well into the wild.
The good news is that there are strains of salmonoids that are more resistant to Myxobolus cerebralis than others. This includes avoiding earthen ponds to raise young fish. Instead, smooth-faced concrete or plastic-lined raceways that are kept clean regularly and are free of any contaminated water will keep aquaculture facilities free of whirling disease.
There are some drugs which have shown to impede spore development and therefore will reduce infection rates. These include clamoxyquine, proguanil, fumagillin, benomyl, furoxone, and furazolidone. However, this is unsuitable for wild trout populations.
Sports and recreational anglers can help to prevent the spread of Myxobolus cerebralis in several ways. This includes cleaning fishing equipment between fishing trips, not transporting a fish between different body of waters to avoid cross-contamination of water ways, and not disposing of any fish entrails or bones in the waterways. In addition, salmonoids should never be used as bait.