Whirling Disease: Reviews and Current Topics

<em>ABSTRACT. </em>The ability of several compounds to discharge the polar filaments of polar capsules of the triactinomyxon stage of <em>Myxobolus cerebralis </em>was tested. Premature polar filament discharge may provide a means for preventing the infective stage of myxozoan parasites from attaching to fish hosts. The discharge regimes evaluated included high and low pH, chloride and phosphate salts, calcium chelators, direct current, mucus, tricaine methanesulfonate anesthetic, neurochemicals, and chemosensitizing agents that are effective discharge agents for members of the phylum Cnidaria. Polar filament discharge, in response to HCl or NaOH, did not differ from controls until pH levels dropped to 1.1 or increased to 11.7. Among the chloride salts tested (NaCl, KCl, CaCl₂, NH₄Cl, MgCl₂), discharge increased at concentrations ranging from 3.1 to 100‰. Discharge varied among the salts tested, peaking at 71% for 100‰ KCl; however, the phosphate salts K⁺and Na⁺did not differ in discharge ability. Comparison among KCl, KI, and KPO₄indicated that Cl^-was significantly more effective at both 6.2‰ (45.6% discharge) and 12.5‰ (57.8%) than the other anions. The calcium chelators sodium citrate and EGTA did not induce any significant increase in discharge, nor did the neurochemicals angiotensin, bradykinin, and acetylcholine chloride. Compounds, such as N-acetyl neuraminic acid, proline, and glutathione, that have been reported as chemosensitizers for cnidae discharge among cnidarians, were ineffective discharge agents for triactinomyxon polar capsules. Mucus from rainbow trout or bovine submaxillary gland failed to significantly increase discharge. Attempts to combine mucus with force (stirring rod) or a 0.45 Gauss magnetic field did not increase discharge rates. However, using an electroporator to administer direct current, the discharge rate increased with pulse length (up to 99 µsec) and the number of pulses (0–25). Maximum discharge (98%) and mortality (100%) was observed after 25 99-µsec pulses of 3 kV. Results with electricity indicate a potential for using direct current as a means of disinfection. The data suggest some similarities and differences with similar research on Cnidaria that is discussed.