As part of Work Package 1 (Host-parasite Interactions), the Hungarian Academy of Sciences (MTA) and the Biology Centre of the Academy of Sciences of the Czech Republic (BCAS) together with Chinese researchers, studied the life cycle of Thelohanellus spp. parasitising common carp.
Thelohanellus nikolskii plasmodia containing
myxospores on the scales of a three-year-old common carp
Two species of Thelohanellus, T. nikolskii and T. hovorkai, were introduced into Central Europe in the 1970s from the Far East where they originally infected the eastern sub-species of common carp (Cyprinus carpio haematopterus). Until now T. nikolskii, a species destroying the fins of carp, has been regarded by fish farmers as the most pathogenic species.
Recently, a new species of Thelohanellus, T. kitauei, has emerged in Asia, causing severe symptoms of intestinal giant-cystic disease in the gut of infected carp.
MTA and BCAS studies of the T. kitauei presence in central Europe from pond water and from alternate oligochaete hosts (see picture on the left) and from the fish host, common carp, has revealed that the Hungarian T. kitauei samples are closely related to the Asian samples, but there is a difference in their pathogenicity; the myxozoan stage and the giant cyst symptoms have not been detected to date in the Hungarian samples. This is good news for Central European common carp fish farmers, as myxosporean-associated parasitosis is responsible for severe pathological changes and economic losses in cultured common carp.
Floating aurantiactinomyxon spore stages of T. kitauei in
water released by the invertebrate alternate host,
Branchiura sowerbyi. T. kitauei myxospores are the
causative agent of the giant cystic disease of common carp in Asia