[9] Infected oligochaete worms were first discovered in Hungary and raised concerns of the introduction of T. kitauei into European carp culture ponds, since it was believed to be endemic to Asia.

Branchiura sowerbyi (Oligochaeta, Naididae, Branchiurinae) is the definitive host, in which actinosporean spores of the aurantiactinomyxon type are formed and released from the intestinal tract of the worms.

A qPCR detection assay was developed by Seo et al.,[11] but its specificity requires confirmation as closely related species show only minor 18S rDNA sequence divergence.

Most research on this parasite is performed in Japan, China and Korea, where IGCD affects a large number of carp stocks.

Within the EU-funded Horizon 2020 Project ParaFishControl the invertebrate host of T. kitauei was elucidated in Hungary, though this country is thought to be an IGCD-free carp culture area.

Ongoing studies within this project investigate the presence of T. kitauei in environmental samples in carp culture ponds in different countries in Europe and focus on detecting a potentially different infection site in fish, as large scale screening of intestines did not reveal T. kitauei infections, even at sites where the parasite was detected in environmental samples.