Associated disease risk from the introduced generalist pathogen Sphaerothecum destruens: management and policy implications

Abstract

The rosette agent Sphaerothecum destruens is a novel pathogen, which is currently believed to have been introduced into Europe along with the introduction of the invasive fish topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel, 1846). Its close association with P. parva and its wide host species range and associated host mortalities, highlight this parasite as a potential source of disease emergence in European fish species. Here, using a meta-analysis of the reported S. destruens prevalence across all reported susceptible hosts species; we calculated host-specificity providing support that S. destruens is a true generalist. We have applied all the available information on S. destruens and host-range to an established framework for risk-assessing non-native parasites to evaluate the risks posed by S. destruens and discuss the next steps to manage and prevent disease emergence of this generalist parasite.

Keywords: Europe; Pseudorasbora parva; aquatic ecosystems; biodiversity threat; disease emergence; topmouth gudgeon.

Fig. 1.

Hierarchical taxonomic tree for all currently known hosts (n = 14) of Sphaerothecum destruens. A: Oncorhynchus tshawytscha (Chinook salmon), B: O. kisutch (Coho salmon), C: O. mykiss (rainbow trout), D: Salmo trutta (brown trout), and E: S. salar (Atlantic salmon) The Cyprinidae is represented by seven species belonging to seven genera; F: Cyprinus carpio (carp), G: Rutilus rutilus (roach), H: Abramis brama (bream), J: Leucaspius delineatus (sunbleak); K: Squalius fellowesii. In the calculation of host specificity, the species Pseudorabora parva (topmouth gudgeon; Family Cyprinidae), the species Oxynoemachelius sp. (Family Nemacheilidae) and Lepomis gibbosus (Family Centrachidae) were also included. The host specificity (STD) was calculated to be 3·82 with a variance of 0·49.

Fig. 2.

Risk assessment to determine whether management options to control the spread of Sphaerothecum destruens. The decision diagram has been adapted from Williams et al. (2013). The risk assessment follows the potential hazard assessment posed by the parasite. Refer to the section Results for the rationale supporting the decision made at each step and to Williams et al. (2013) for module 2.