Parasite	Thelohanellus hovorkai
Taxonomy	Myxozoa, Myxosporea, Bivalvulida
Host	Common carp (Cyprinus carpio)
Disease name	Haemorrhagic thelohanellosis
Infection site	Subcutaneous connective tissue
Clinical signs	Diseased fish are emaciated and anorexic followed by the death. The clinical signs of moribund fish are characterized by petechial, scattered haemorrages on the body surface (Fig. 1).
Parasitology	Many spores are observed in the skin mucus of diseased fish (Fig. 2). A spore (length 18.0-21.0 (average 20.1) mm; width 9.5-10.5 (10.2) mm) is ovoid in shape and has one subspherical polar capsule (length 7.5-10.5 (9.2) mm; width 6.5-9.5 (8.2) mm). A spore is surrounded by a loose membranous envelope, and the total length of a spore is ca. 24.4 mm (Yokoyama et al., 1998). Aurantiactinomyxon actinosporean develops in an oligochaete Branchiura sowerbyi, invades the fish and transforms to a myxospore of T. hovorkai (Yokoyama, 1997).
Pathology	T. hovorkai infects not only to the subcutaneous tissue but also to the connective tissue of the various organs. After maturation of the parasite, spores are dispersed into the neighboring tissues and cause extensive inflammation, haemorrhages, aedema and exfoliation of the epithelium (Yokoyama et al., 1998).
Health hazard	Since this parasite is not infectious to human, it is harmless in food hygiene.
Diagnosis	Check the spores by wet-mount of mucus in the lesion. Sample should be smeared and stained by Diff-Quik.
Other information	In the mid-1990s, a disease outbreak occurred in adult (2- and 3-year old) color carp at a culture pond in Niigata Prefecture (Yokoyama et al., 1998). This species is one of the most studied myxosporeans in Japan, since the life cycle was revealed and thus the experimental infection can be readily completed. The parasite can invade the host through both the gill and the gut. Massive ingestion of the oligochaetes is an important aetiological factor since the clinical disease is more easily achieved using the oral intubation of actinospores than by immersion in an actinospore suspension (Liyanage et al., 1998; 2003a). Some control methods for this disease was proposed. The oligochaetes can be removed by replacing muddy bottom to sandy bottom (Liyanage et al., 2003b) or using benthos-eating fishes (Yokoyama et al., 2002). Chemotherapy with fumagillin has been reported to be effective (Yokoyama et al., 1999).
References	Liyanage, Y. S., H. Yokoyama, H. Matoyama, H. Hosoya and H. Wakabayashi (1998): Experimentally induced hemorrhagic thelohanellosis of carp caused by Thelohanellus hovorkai (Myxosporea: Myxozoa). Fish Pathol., 33, 489-494. Liyanage, Y. S., H. Yokoyama and H. Wakabayashi (2003a): Dynamics of experimental production of Thelohanellus hovorkai (Myxozoa: Myxosporea) in fish and oligochaete alternate hosts. J. Fish Dis., 26, 575-582. Liyanage, Y. S., H. Yokoyama and H. Wakabayashi (2003b): Evaluation of a vector control strategy of haemorrhagic thelohanellosis in carp, caused by Thelohanellus hovorkai (Myxozoa). Dis. Aquat. Org., 55, 31-35. Yokoyama, H. (1997): Transmission of Thelohanellus hovorkai Achmerov, 1960 (Myxosporea: Myxozoa) to common carp Cyprinus carpio through the alternate oligochaete host. Syst. Parasitol., 36, 79-84. Yokoyama, H., Y. S. Liyanage, A. Sugai and H. Wakabayashi (1998): Hemorrhagic thelohanellosis of color carp caused by Thelohanellus hovorkai (Myxozoa: Myxosporea). Fish Pathol., 33, 85-89. Yokoyama, H., Y. S. Liyanage, A. Sugai and H. Wakabayashi (1999): Efficacy of fumagillin against haemorrhagic thelohanellosis caused by Thelohanellus hovorkai (Myxosporea: Myxozoa) in coloured carp, Cyprinus carpio L. J.Fish Dis., 22, 243-245. Yokoyama, H., Y. S. Liyanage and H. Wakabayashi (2002): A new strategy against myxosporean diseases: vector control in hemorrhagic thelohanellosis of cultured carp. Fish. Sci., 68 (Suppl. I), 825-828.