Stellantchasmus falcatus is one of the minute intestinal trematodes of fish-eating birds and mammals such as cats, dogs, and rats (
Onji and Nisho, 1924;
Takahashi, 1929). The second intermediate hosts, possible sources of human infections, are several kinds of brackish and freshwater fishes (
Chai and Sohn, 1988;
Waikagul, 1998). Natural human infections have been reported in the Philippines (
Africa and Garcia, 1935), Hawaii (
Alicata and Schattenburg, 1938), Japan (
Kagei, 1964), and Thailand (
Radomyos et al., 1990). Also, five human cases of
S. falcatus infection have been reported in Korea (
Seo et al., 1984;
Sohn et al., 1989;
Son et al., 1994).
From a 66-year-old Korean man who was living in Namhae-gun, Kyongsangnam-do, Korea, and was suffering from chronic viral hepatitis, unidentified helminth eggs were found during a routine stool examination. The unidentified egg, 39 µm by 22 µm in size, was elliptical and was light yellow in color. The shell surface was smooth and the operculum was inconspicuous. The man had a infrequent history of eating raw flesh of several kinds of brackish water fish. He experienced no subjective gastrointestinal troubles.
To collect and identifiy the worm producing the unidentified egg, the patient was treated with a single dose of 10 mg/kg praziquantel and purged with magnesium sulfate. Diarrheal stools were collected, washed, and sedimented with physiological saline. Through scrutinizing the fecal sediments under a dissecting microscope, one fluke was collected and was identified as
Stellantchasmus falcatus on the basis of morphological characteristics. The fluke was ovoid, 480 µm long and 322 µm wide. The whole surface of the body was covered with scale-like minute tegumental spines (
Fig. 1). The ventrogenital sac located in the midmedian of the body and contained the ventral sucker armed with minute spines. Seminal vesicles were bipartite into the proximal thin-walled and distal strongly thick-walled muscular (expulsor) parts. The expulsor was oblique and sinistral to the median line between the ventral sucker and ovary. The ovary was facing slightly towards the right. The shape of intra-uterine egg (26 µm by 15 µm) was ovoid and operculated.
Morphological findings of the fluke collected from this patient agreed well with respect to the previous report on
S. falcatus (
Seo et al., 1984) such as the presence of the expulsor, the location and constitution of the ventrogenital sac, and the relative location of the ovaries and testes. It is probable from the patient's episode that some brackish water fish may have been the source of infection (
Chai and Sohn, 1988;
Sohn et al., 1989).
The eggs of
S. falcatus, which are found in the uteri or in the fecal samples of the patients, are operculated with a range 23-27 µm in length and 10-14 µm in width (
Seo et al., 1984;
Sohn et al., 1989;
Radomyos et al., 1990). The unidentified egg found in the subjected patient was unoperculated and was larger in size than the reported
S. falcatus eggs; hence, the unidentified eggs were not of
S. falcatus. Since natural human infection by
S. falcatus have been reported from several cases by intestinal flukes, it was not easy to say specific symptoms provoked by
S. falcatus (
Seo et al., 1984;
Hong et al., 1986;
Sohn et al., 1989;
Son et al., 1994). Heterophyid flukes produce a small amount of eggs per day (
Chai and Lee, 1990). Therefore, with limited eggs available, it is difficult to assess possible infection through a routine stool examination, especially with light worm burden cases. Previous
S. falcatus cases reported in Korea were encountered by an unintentional collection of intestinal flukes from diarrheal stools after anthelminthic adminstrations. Therefore, it can be speculated that there would be many undetected cases of heterophyid infection other than
Metagonimus spp. in Korea, especially in towns and villages along the coast of the Korean peninsula.
References
- 1. Africa CM, Garcia EY. Heterophyid trematodes from man and dogs in the Philippines with description of three new species. Phil J Sci 1935;57:253-267.
- 2. Alicata JE, Schattenburg OL. A case of intestinal heterophyidiasis of man in Hawaii. J Am Med Ass 1938;110:1100-1101.
- 3. Chai JY, Lee SH. Intestinal trematodes of humans in Korea: Metagonimus, heterophyids and echinostomes. Korean J Parasitol 1990;28:103-122.
- 4. Chai JY, Sohn WM. Identification of Stellantchasmus falcatus metacercariae encysted in mullets in Korea. Korean J Parasitol 1988;26:65-68.
- 5. Hong ST, Chai JY, Lee SH. Ten human cases of Fibricola seoulensis infection and mixed one with Stellantchasmus falcatus and Metagonimus. Korean J Parasitol 1986;24:95-97.
- 6. Kagei N, Oshima T, Ishikawa K, Kihata M. Two cases of human infection with Stellantchasmus falcatus Onji et Nisho, 1915 (Heterophyidae) in Kochi Prefecture. Jpn J Parasitol 1964;13:472-478. (in Japanese).
- 7. Onji Y, Nisho T. A monograph of intestinal trematodes. Chiba Igakkai Zasshi 1924;2:113-161. (in Japanese).
- 8. Radomyos P, Charoenlarp P, Radomyos B, Tungtrongchitr A. Two human cases of Stellantchasmus falcatus (Trematoda, Heterophyidae) infection in northern Thailand. Jpn J Parasitol 1990;39:7-11.
- 9. Seo BS, Lee SH, Chai JY, Hong SJ. Studies on intestinal trematodes in Korea XII. Two cases of human infection by Stellantchasmus falcatus. Korean J Parasitol 1984;22:43-50.
- 10. Sohn WM, Chai JY, Lee SH. A human case of Stellantchasmus falcatus infection. Korean J Parasitol 1989;27:277-279.
- 11. Son WY, Huh S, Lee SU, Woo HC, Hong SJ. Intestinal trematode infections in the villagers in Koje-myon, Kochang-gun, Kyongsangnam-do, Korea. Korean J Parasitol 1994;32:149-155.
- 12. Takahashi S. On the eggs of several kinds of intestinal trematodes, which resemble that of Clonorchis sinensis, especially the eggs of Stellantchasmus falcatus and Pygidiopsis summus found in human stools with a supplement on the examination of the helminthic parasites of the dogs and cats in Okayama prefecture. Okayama Igakkai Zasshi 1929;41:1502-1513. (in Japanese).
- 13. Waikagul J. Opisthorchis viverrinii metacercaria in Thai freshwater fish. Southeast Asian J Trop Med Public Health 1998;29:324-326.
Fig. 1
Stellantchasmus falcatus adult worm (unstained) showing a muscular expulsor (EP) collected from the patient. Bar=100 µm.
Citations
Citations to this article as recorded by
- Digestive tract trematodiases caused by members of the Heterophyidae
S. B. Chuelov, A. L. Rossina
CHILDREN INFECTIONS.2021; 20(1): 39. CrossRef - Epidemiological situation and molecular identification of cercarial stage in freshwater snails in Chao-Phraya Basin, Central Thailand
Sothorn Anucherngchai, Thanawan Tejangkura, Thapana Chontananarth
Asian Pacific Journal of Tropical Biomedicine.2016; 6(6): 539. CrossRef - Stellantchasmus falcatus (Digenea: Heterophyidae) in Cambodia: Discovery of Metacercariae in Mullets and Recovery of Adult Flukes in an Experimental Hamster
Jong-Yil Chai, Woon-Mok Sohn, Byoung-Kuk Na, Hoo-Gn Jeoung, Muth Sinuon, Duong Socheat
The Korean Journal of Parasitology.2016; 54(4): 537. CrossRef - Digenean metacercariae of fishes from the lagoon flats of Palmyra Atoll, Eastern Indo-Pacific
V.M. Vidal-Martínez, M.L. Aguirre-Macedo, J.P. McLaughlin, R.F. Hechinger, A.G. Jaramillo, J.C. Shaw, A.K. James, A.M. Kuris, K.D. Lafferty
Journal of Helminthology.2012; 86(4): 493. CrossRef
