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Prophylactic and therapeutic studies on intestinal giant-cystic disease of the Israel carp caused by Thelohanellus kitauei. I. Course of formation and vanishment of the cyst
J K Rhee,J O Kim,P G Kim and B K Park
Department of Parasitology, School of Veterinary Medicine, Chonbuk National University, Cheonju 560-756, Korea.
Abstract
In an attempt to develop prophylactic and therapeutic measures of the intestinal giant-cystic disease caused by Thelohanellus kitauei in the Israel carp, Cyprinus carpio nudus, pathological observations were conducted upon the carps which were hatched in May 1988 and raised in a net cage fish farm at the Soyang lake, managed by Horim Fisheries for the period of 21 months with 1-2 months interval. After a gross inspection of the carps, necropsy was carried out periodically in order to clarify the pathological changes in various internal organs and muscular tissues. Also, the prevalence of the disease was checked during the period from 1988 to 1990.
Gross inspections revealed that the infected carps showed some degree of fading in body and gill color, back-emaciation symptoms, reddish anus accompanying erosion and relaxation and pot-belly, as well as discharge of yellowish white mucoid material from the anus. However, most carps died eventually of intestinal obstruction. Other significant necropsy findings included cyst formation of various size in the intestinal mucosa, ascites, anemic condition through internal organs and muscular tissues, hyperemia and dilation of intestines with decreased tension, thinness and fragility, and full contents of semi-fluid or yellowish white mucoid material in the intestinal canals.
Based on the morphological characteristics of the spores found in the cysts, parasitic location in the intestines, macro- and microscopic findings of the lesions, the parasites were identified as Thelohanellus kitauei Egusa et Nakajima, 1981. Although monthly changes of water temperature were distinct, the extrusion rates of the polar filaments of the spores stayed constant throughout the year with an exception of a lower rate in July. The lesions initiated from mucosa and submucosa in early July became large swellings and then complete mature forms following the peracute course. From late August the upper cysts were gradually opened and most of the spores were dispersed from anus into the surrounding water through December but only a few lasted until next April. The cysts were completely recovered until next September.
Comparing the incidence and prevalence of the disease by year tremendous infection and death rates were checked in the first prevalent year, 1988, but the rates were significantly decreased in the second year, and showed an almost normal status in the third year, 1990. As the above summarized results showed, the disease entity might come to an end in three years after the first prevalent year, however, the spores must be strictly prevented because they could be infective in the water for one year.
Figures
Figs. 1-6 Fig. 1. A small yellowish-white lesion over the intestinal mucosa of a healthy 14-month-old Israel carp in July 6, 1989.
Fig. 2. A section of an initial lesion caused by a winding tubular vegetative form. A large number of cross sections of immature vegetative form are observed in lamina propria and submucosa of the intestine of a 14-month-old Israel carp in July 6, 1989. ×40.
Fig. 3. Live spores of Thelohanellus kitauei are found in water. ×400.
Fig. 4. The youngest plasmodium of T. kitauei is surrounded by granular wandering cells and lymphocytes, and a large number of small or large nuclei stained deeply by hematoxylin are observed in the plasmodium of a section from a small visible lesion under the mucosa of a 14-month-old Israel carp in July 6, 1989. ×400.
Fig. 5. The thick encapsulation(arrow) is composed of new or old connective tissues accompanied by various inflammatory cells and intestinal columnar epithelia in a 14-month-old Israel carp in July 26, 1989. ×40.
Fig. 6. A cross section of a mature single tubular vegetative form is surrounded by tortuous newly formed sinusoidal capillaries filled with erythrocytes in a 15-month-old Israel carp in August 2, 1989. ×200.
*Figures 2,4,5&6; H-E or Giemsa stained.
Figs. 7-12 Fig. 7. A part of the section of a giant swelling (41×58 mm in size) is filled up with a mature single tubular vegetative form and numerous spores fill all parts of the cross section in a 16-month-old Israel carp in September 7, 1989. ×100.
Fig. 8. The cross sections of some atrophic cysts (3×7 mm in size) show collapsed connection of newly formed loose connective tissue, a few solitary mature spores, and diffuse infiltration of a few lymphocytes and numerous granular wandering cells in a 18-month-old Israel carp in November 15, 1989. ×100.
Fig. 9. Typical small swelling(cysts) are developed on the mucosa in a 16-month-old Israel carp in September 7, 1989.
Fig. 10. A giant swelling (41×58 mm in size) is formed in the mucosa in a 16-month-old Israel carp in September 7, 1989.
Fig. 11. Newly formed capillaries are filled up with lymphocytes and erythrocytes and free spores are found from broken part of the swelling in a 16-month-old Israel carp in September 7, 1989. ×100.
Fig. 12. Some cross sections of highly degenerated tubular vegetative form are replaced with massive hyperplastic connective tissue, meanwhile decreased number of mature spores and a number of lymphocytes are found over intra- and extra-cross sections in a broken swelling (21×15mm in size) in a 18-month-old Israel carp in November 15, 1989. ×40.
*Figures 7, 8, 11 & 12: H-E or Giemsa stained.
Figs. 13-18 Fig. 13. A number of cross sections, which are filled up with the spores, of a mature tubular vegetative form are observed, and the cross sections are surrounded by an abnormally developed mucosal tissue of the intestine in combination with proliferated connective tissues in a 19-month-old Israel carp in December 1, 1989. ×40.
Fig. 14. A number of small vacuoles and some spores are observed in extra- or intra-trace of the cross sections in a 20-month-old Israel carp in January 25, 1990. ×100.
Fig. 15. Connective tissue shows moderate proliferation where some spores and their debris are recognized in a cross section in a weak 21-month-old Israel carp in February 20, 1990. ×100.
Fig. 16. Infiltration of lymphocytes and some spores freed from the cross sections are recognized in broken part of the cyst after bursting in a weak 21-month-old Isreal carp in February 20, 1990. ×200.
Fig. 17. A number of lymphocytes with a few erythrocytes and spores are found from a confluent cross section in a weak 23-month-old Israel carp in April 28, 1990. ×100.
Fig. 18. A number of degenerated spores which are scarcely staind with H-E stain are distributed throughout the cyst and fibroblasts are proliferated around the spores in a weak 23-month-old Israel carp in August 2, 1990. ×400.
*Figures 13-18: H-E or Giemsa stained.
Tables
Table 1 Effects of various concentrations of KOH on extrusion rates of polar filaments of Thelohanellus kitauei spores
Table 2 Effects of seasons on extrusion rates of polar filaments of T. kitauei spores
Table 3 prevalence of T. kitauei in Cyprinus carpio nudus in net cage fish farm at the Soyang lake managed by Horim Fisheries
References
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Egusa S, et al. Fish Pathol 1981;15(3/4):213–218.
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Molnar K. Biology and histopathology of Thelohanellus nikolskii Achmerov, 1955 (Myxosporea, Myxozoa), a protozoan parasite of the common carp (Cyprinus carpio). Z Parasitenkd 1982;68(3):269–277.
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Molnar K, et al. Parasit Hung 1981&1982;14:51–54.
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Molnar K, Kovacs-Gayer E. Biology and histopathology of Thelohanellus hovorkai Achmerov, 1960 (Myxosporea, Myxozoa), a protozoan parasite of the common carp (Cyprinus carpio). Acta Vet Hung 1986;34(1-2):67–72.
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