Effect of cadmium on the susceptibility of Tubifex tubifex to Myxobolus cerebralis (Myxozoa), the causative agent of whirling disease

Abstract

Environmental pollutants alter a wide range of host-parasite interactions in various ways. In some cases, pollution leads to a significant increase in parasite abundance, causing epidemics of parasitic diseases. In other cases, toxicants restrict the transmission success of parasites, resulting in reduction of their abundance. However, very little is known regarding whether and to what extent aquatic pollution affects myxozoan obligate parasites commonly found in fish. We investigated the effect of cadmium (Cd) on the aquatic oligochaete Tubifex tubifex infected with the myxozoan Myxobolus cerebralis. The oligochaetes were experimentally exposed to M. cerebralis myxospores and kept in various concentrations of Cd for 4 mo. Neither survival nor reproduction of the worms was affected by the metal, but infection prevalence and numbers of triactinosmyxon spores produced by individual worms were higher in the Cd-exposed group than the unexposed control. A comparative assay of a lethal Cd concentration (LC50) on infected and non-infected T. tubifex revealed that infected worms are more resistant to the acute toxicity of Cd, probably because uptake of Cd was reduced by the infection. These results suggest that the abundance of M. cerebralis likely increases in polluted waters and escalates the risk of whirling disease in the respective area.