Evaluation of a vector-control strategy ofhaemorrhagic thelohanellosis in carp, causedby Thelohanellus hovorkai (Myxozoa)

[摘要] ABSTRACT: The life cycle of Thelohanellus hovorkai (Myxozoa), the causative agent of haemorrhagic thelohanellosis of carp Cyprinus carpio, involves the alternate oligochaete host Branchiura sowerbyi, which plays the role of vector inthe parasite¹s transmission. Field investigations in carp farms suggested that oligochaete fauna were closely associated with the substrate type of the pond. The pond bottom in the enzootic farm consisted of clay soil and soft sediments comprised oforganic mud, in which B. sowerbyi dominated in high densities, with a maximum of 5.6 ind. kg^-1 soil. In another case, in a carp farm with no previous history of the disease, the pond bottom was sandy soil, in which small-sizedoligochaetes, composed mainly of Limnodrilus socialis, dominated. Laboratory studies on the substrate preference of oligochaetes proved that B. sowerbyi prefers mud to sand, whereas L. socialis has no tendency to substratetropism. The delicate body surface of B. sowerbyi was subject to damage by rugged-edged sand particles, which inflicted severe injuries to the worms. Transmission experiments showed that L. socialis, which are non-susceptible to T.hovorkai, suppressed the production of T. hovorkai actinospores in B. sowerbyi in a mixed assemblage of oligochaetes. Field and experimental evidence in this study imply that substrate replacement in culture ponds might regulatethe benthic oligochaete communities, resulting in minimization of the impact of haemorrhagic thelohanellosis. We propose that ecological control of oligochaete fauna by environmental management is a promising strategy against myxozoan diseases.

[学科分类] 生物科学（综合）

[关键词] Thelohanellus hovorkai;Common carp;Cyprinus carpio;Branchiura sowerbyi;Vector control;Myxosporean;Actinosporean