Volume 17, Number 7—July 2011
Adult Opisthorchis viverrini Flukes in Humans, Takeo, Cambodia
To the Editor: Opisthorchis viverrini and Clonorchis sinensis, the 2 major species of small liver flukes (family Opisthorchiidae), cause chronic inflammation in the bile duct, which leads to cholangitis and cirrhosis of the liver, and are a predisposing factor for cholangiocarcinoma (1). Human infections with O. viverrini flukes are found along riverside areas of Indochina (Thailand, Lao People’s Democratic Republic [PDR], and Vietnam) (2).
Small trematode eggs (length 20–32 μm) have been found in human fecal samples in Cambodia (1,3,4). During 1981–1982, two of 102 Cambodian refugees in the United States were found to be positive for C. sinensis (likely O. viverrini) eggs (3). Egg-positive cases were later detected in several provinces of Cambodia (4,5). Presence of O. viverrini flukes in Cambodia was verified by detection of metacercariae in freshwater fish in a lake on the border between Takeo and Kandal Provinces and by isolation of adult flukes in experimentally infected hamsters (6).
In May 2010, we analyzed fecal samples from 1,993 persons in 3 villages (Ang Svay Chek, Kaw Poang, and Trartang Ang) in the Prey Kabas District, Takeo Province, Cambodia, ≈45 km south of Phnom Penh, to confirm the presence of O. viverrini flukes among humans. We found an egg-positive rate of 32.4% for small trematode eggs. Because these eggs may be those of Haplorchis spp. flukes (H. taichui, H. pumilio, and H. yokogawai) and lecithodendriid flukes (Prosthodendrium molenkampi and Phaneropsolus bonnei) (1), we attempted to detect adult flukes that are responsible for these eggs.
Six of the small trematode egg–positive villagers, 1 man and 5 women (age range 16–72 years), who had occasional epigastric discomfort were selected for anthelmintic treatment, purgation, and recovery of adult worms. Fecal examination and anthelmintic treatment of villagers were approved by the Ministry of Health, Cambodia, under the agreement with the Korea–Cambodia International Collaboration on Intestinal Parasite Control in Cambodia (2006–2011). After obtaining informed consent, the villagers were treated with a single oral dose of praziquantel, 40 mg/kg (Shinpoong Pharmaceutical Co., Seoul, South Korea), and given a purgament (solution containing 30–40 g MgSO4). Feces was obtained 3 or 4 times in a 2–3-hour period after purgation, pooled individually, and processed as described (7). Worms obtained were fixed with 10% formalin, stained with acetocarmine, and identified by morphologic features.
A total of 34 O. viverrini adult worms were obtained from the 6 villagers (14, 9, 5, 3, 2, and 1 from each villager, respectively). No other species of trematodes were obtained. Five worms were lanceolate and had a mean length of 9.5 mm (range 6.5–12.0 mm), a mean width of 1.5 mm (range 1.2–1.7 mm), and 2 characteristic 4–5-lobulated testes (Figure, panel A). Ten eggs in uteri were 27 μm long (range 25–29 μm) and 15 μm wide (range 13–16 μm).
To detect the source of infection, 2 freshwater fish species, Puntioplites proctozysron (n = 5) and Cyclocheilichthys apagon (n = 10), were caught in nearby Ang Svay Chek village and examined for O. viverrini metacercariae by using a digestion technique (8). A total of 50 metacercariae (Figure, panel B) were obtained from 5 P. proctozysron fish and fed to a hamster. Six weeks later, 42 young O. viverrini flukes (Figure, panel C) were isolated from the biliary tract of the hamster.
Our study identified only O. viverrini infections in humans in Cambodia. However, eggs of other hepatic and intestinal flukes also can be found in humans (1). In Thailand, Vietnam, and Lao PDR, opisthorchiids (O. viverrini and C. sinensis), heterophyids (Haplorchis spp., Centrocestus formosanus, and Stellantchasmus falcatus), and lecithodendriids have been found in humans (1,7,9). In several provinces in Lao PDR, mixed infections with O. viverrini and heterophyids or lecithodendriids were common (7,9), and the relative prevalence of each fluke species varied by locality. In Vientiane, Lao PDR, O. viverrini was the predominant species, whereas in Saravane Province, H. taichui predominated (7). In a mountainous area of Phongsaly Province, H. taichui and H. yokogawai worms were obtained from 10 villagers; however, no O. viverrini worms were detected (10). Thus, in Cambodia, the presence of human infections with intestinal flukes, including Haplorchis spp. and lecithodendriids, cannot be ruled out.
We thank the staff of the Centre for Parasitology, Entomology, and Malaria Control, Phnom Penh, Cambodia, and Dong-Min Lee, Yoon-Hee Lee, Ji-Hae Kang, Hyun-Ju Woo, and Jun-Yong Hong for assistance with Kato-Katz fecal examinations.
- Chai JY, Murrell KD, Lymbery AJ. Fish-borne parasitic zoonoses: status and issues. Int J Parasitol. 2005;35:1233–54.
- Andrews RH, Sithithaworn P, Petney TN. Opisthorchis viverrini: an underestimated parasite in world health. Trends Parasitol. 2008;24:497–501.
- Parish RA. Intestinal parasites in Southeast Asian refugee children. West J Med. 1985;143:47–9.
- Stich AH, Biays S, Odermatt P, Men C, Saem C, Sokha K, Foci of Schistosoma mekongi, northern Cambodia: II. Distribution of infection and morbidity. Trop Med Int Health. 1999;4:674–85.
- Lee KJ, Bae YT, Kim DH, Deung YK, Ryang YS, Kim HJ, Status of intestinal parasites infection among primary school children in Kampongcham, Cambodia. Korean J Parasitol. 2002;40:153–5.
- Touch S, Komalamisra C, Radomyos P, Waikagul J. Discovery of Opisthorchis viverrini metacercariae in freshwater fish in southern Cambodia. Acta Trop. 2009;111:108–13.
- Chai JY, Park JH, Han ET, Guk SM, Shin EH, Lin A, Mixed infections with Opisthorchis viverrini and intestinal flukes in residents of Vientiane Municipality and Saravane Province in Laos. J Helminthol. 2005;79:283–9.
- Rim HJ, Sohn WM, Yong TS, Eom KS, Chai JY, Min DY, Fishborne trematode metacercariae detected in freshwater fish from Vientiane Municipality and Savannakhet Province, Lao PDR. Korean J Parasitol. 2008;46:253–60.
- Chai JY, Han ET, Shin EH, Sohn WM, Yong TS, Eom KS, High prevalence of Haplorchis taichui, Prosthodendrium molenkampi, and other helminth infections among people in Khammouane Province, Lao PDR. Korean J Parasitol. 2009;47:243–7.
- Chai JY, Yong TS, Eom KS, Min DY, Shin EH, Banouvong V, Prevalence of the intestinal flukes Haplorchis taichui and H. yokogawai in a mountainous area of Phongsaly Province, Lao PDR. Korean J Parasitol. 2010;48:339–42.
Suggested citation for this article: Sohn W-M, Shin E-H, Yong T-S, Eom KS, Jeong H-G, Sinuon M, et al. Adult Opisthorchis viverrini flukes in humans, Takeo, Cambodia [letter]. Emerg Infect Dis [serial on the Internet]. 2011 Jul [date cited]. http://dx.doi.org/10.3201/eid1707.102071
1These authors contributed equally to this article.
Comments to the Authors
Comments to the EID Editors
Please contact the EID Editors via our Contact Form.
- Page created: August 18, 2011
- Page last updated: August 18, 2011
- Page last reviewed: August 18, 2011
- Centers for Disease Control and Prevention,
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
Office of the Director (OD)