Studying the life cycles of Thelohanellus spp.


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 pic

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.

Thelohanellus spp. 2

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



Improved Control of Parasitic Worms

Good news for European consumers of farmed fish! A ParaFishControl recent study, carried out by Work Package 7 (Fish Product Safety), demonstrated the absence of zoonotic parasitic worms in European farmed fish, specifically in gilthead sea bream, European sea bass, turbot, Atlantic salmon, rainbow trout and common carp at a confidence level of 95-99%. From spring 2016 to winter 2017, more than 7,000 fish were analysed from commercial aquaculture farms throughout Europe, including Croatia, Denmark, Greece, Hungary, Italy, Norway, Spain, and Turkey.

In addition, with the aim of greater control of the presence of Anisakis parasites in marine farmed fish species, AZTI has developed the Rapid Kit for the Identification of Anisakis. For the very first time it is possible to identify Anisakis simplex (excluding DNA isolation) within 15 minutes! This cheap, portable, and user-friendly kit could become a valuable tool in the future to certify that fish farmed in the EU is grown in an environment free of Anisakis.

Rapid Kit

Workshop on “Sustainable Fish Health Control”

The DAFINET workshop on Sustainable fish health control was organized in collaboration with Parafishcontrol and BANGFISH on October 23, 2018. In connection to the workshop the University of Copenhagen hosted a five day workshop on fish diseases. The 40 workshop participants comprised PFC partners and colleagues from various countries (Norway, Bangladesh, India, China, Indonesia, Italy, Denmark). The scientific fields touched upon ranged from PFC parasites (salmon lice, white spot disease parasite Ichthyophthirius multifiliis, zoonotic nematode Contracaecum osculatum), and environmental issues (arsenic substances and antibiotics in fish ponds), pigments in fish flesh, bacterial and viral infections of rainbow trout. The host species discussed ranged from Atlantic salmon and rainbow trout to tilapia and Asian catfish. Sonal Patel from Norway and Morten Limborg from Denmark presented new results and ideas from novel types of approaches in fish disease research – the holistic view on both host, microbiome and the environment. The connected fish disease course over five days focused on both basic classical techniques and more advanced methodologies such as ELISA, immunohistochemistry, histology, PCR, qPCR and DNA sequencing. The course addressed parasitic, bacterial and viral diseases in wild and farmed fish. The photo shows seven course participants from Bangladesh with professor Kurt Buchmann (KU) in the lab.


NEW ParaFishControl article "Hints on T cell responses in a fish-parasite model: Enteromyxum leei induces differential expression of T cell signature molecules depending on the organ and the infection status"

Hints on T cell responses in a fish-parasite model: Enteromyxum leei induces differential expression of T cell signature molecules depending on the organ and the infection status. Parasites & Vectors 11:443.

Enteromyxum leei is a myxozoan parasite that produces a slow-progressing intestinal disease. This parasite invades the paracellular space of the intestinal epithelium and progresses from the posterior to the anterior intestine. The aim of the present study was to gain insights into fish T cell responses in the gilthead sea bream-E. leei infection model using a PCR-array with 30 signature molecules for different leukocyte responses in head kidney, spleen, anterior and posterior intestine.
The PCR-array results suggest that E. leei induced migration of T cells from head kidney to intestines where TH1, CTL and TH17 profiles were activated and kept in balance by the upregulation of regulatory cytokines. These results were partially validated by the use of cross-reacting antibodies and BrdU immunostaining to monitor proliferation. Zap70 immunostaining supported the increased number of T cells in the anterior intestine detected by gene expression, but double staining with BrdU did not show active proliferation of this cell type at a local level, supporting the migration from lymphohaematopoietic tissues to the site of infection. Global analyses of the expression profiles revealed a clear separation between infected and exposed, but non-infected fish, more evident in the target organ. Exposed, non-infected animals showed an intermediate phenotype closer to the control fish.
These results evidence a clear modulation of the T cell response of gilthead sea bream upon E. leei infection. The effects occurred both at local and systemic levels, but the response was stronger and more specific at the site of infection, the intestine. Altogether, this research poses a promising basis to understand the response against this important parasite and establish effective preventive or palliative measures.


Check out all ParaFishControl publications here

NEW ParaFishControl article on Dysregulation of B Cell Activity During Proliferative Kidney Disease in Rainbow Trout

Dysregulation of B Cell Activity During Proliferative Kidney Disease in Rainbow Trout. Frontiers in Immunology.

Proliferative kidney disease (PKD) is a widespread disease caused by the endoparasite Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea). Clinical disease, provoked by the proliferation of extrasporogonic parasite stages, is characterized by a chronic kidney pathology with underlying transcriptional changes indicative of altered B cell responses and dysregulated T-helper cell-like activities. Despite the relevance of PKD to European and North American salmonid aquaculture, no studies, to date, have focused on further characterizing the B cell response during the course of this disease. Thus, in this work, we have studied the behavior of diverse B cell populations in rainbow trout (Oncorhynchus mykiss) naturally infected with T. bryosalmonae at different stages of preclinical and clinical disease. Our results show a clear upregulation of all trout immunoglobulins (Igs) (IgM, IgD, and IgT) demonstrated by immunohistochemistry and Western blot analysis, suggesting the alteration of diverse B cell populations that coexist in the infected kidney. Substantial changes in IgM, IgD, and IgT repertoires were also identified throughout the course of the disease further pointing to the involvement of the three Igs in PKD through what appear to be independently regulated mechanisms. Thus, our results provide strong evidence of the involvement of IgD in the humoral response to a specific pathogen for the first time in teleosts. Nevertheless, it was IgT, a fish-specific Ig isotype thought to be specialized in mucosal immunity, which seemed to play a prevailing role in the kidney response to T. bryosalmonae. We found that IgT was the main Ig coating extrasporogonic parasite stages, IgT+ B cells were the main B cell subset that proliferated in the kidney with increasing kidney pathology, and IgT was the Ig for which more significant changes in repertoire were detected. Hence, although our results demonstrate a profound dysregulation of different B cell subsets during PKD, they point to a major involvement of IgT in the immune response to the parasite. These results provide further insights into the pathology of PKD that may facilitate the future development of control strategies.

Check out all ParaFishControl publications here