Comparative Morphology of Minute Intestinal Fluke Eggs That Can Occur in Human Stools in the Republic of Korea

Abstract

The egg morphology of minute intestinal flukes (MIF) that can occur as human infections in the Republic of Korea, i.e., Metagonimus yokogawai, M. miyatai, M. takahashii, Heterophyes nocens, Heterophyopsis continua, Stellantchasmus falcatus, Stictodora fuscata, Pygidiopsis summa, and Gymnophalloides seoi, was studied in comparison with Clonorchis sinensis. The adult worms were obtained from residents of endemic areas, and their intrauterine eggs were studied and measured using light microscopy; the length, width, length-width ratio (LWR), and Faust-Meleney index (FMI). Several specimens were processed for scanning electron microscopy (SEM), and before gold-coating, the uterine portion of each fluke was etched with a sharp pin in order to expose the eggs. The MIF eggs were ovoid, pyriform, or elliptical with a size range of 21-35×12-21 µm. S. fuscata eggs revealed the highest FMI (largest in the area) and lowest LWR, whereas P. summa eggs showed the lowest FMI and medium LWR. SEM revealed that G. seoi and S. fuscata had remarkably clean shell surface lacking the muskmelon-like structure which is prominent in C. sinensis eggs. In Metagonimus spp., H. continua, H. nocens, and S. falcatus eggs, minute surface ridges were recognizable though less prominent compared with C. sinensis. On the surface of P. summa eggs, thread-like curly structures were characteristically seen. The results revealed that important differential keys for MIF eggs include the length, width, area (FMI), shape of the eggs, and the extent of the muskmelon-like structure or ridges on their shell surface and operculum.

Molecular confirmation of trematodes in the snail intermediate hosts from Ratchaburi Province, Thailand

“…Two species of heterophyid trematodes have been identified in this study, namely, H. taichui and H. pumilio, which are known to infect humans and other mammals, and are widely distributed in many provinces of Thailand such as Chiang Mai, Phitsanulok, Mae Hong Son, Kamphaeng Phet, and Tak [10,23,30], as well as in other close countries, like Lao PDR, Korea and Vietnam [2,5,7,16]. A recent study conducted in Lao PDR revealed that many patients were infected with H. taichui, with a 99.8% of the trematode specimens identified in patients [2].…”

“…Digenetic trematodes, particularly intestinal and liver flukes, are widely distributed in many Asian countries including Korea, Vietnam, Myanmar, Cambodia, Laos and Thailand, and remain a public health problem throughout the region [1][2][3][4][5][6][7]. The heterophyid trematode and some liver flukes can infect mammals and humans who eat raw or uncooked infected-fish species such as Haplorchis taichui (H. taichui) and Haplorchis pumilio (H. pumilio) [2,8,9].…”

“…Freshwater snails and fish typically serve as the intermediate host in most instances [1,6,14,15]. These trematodes are endemic throughout the Southeast Asian region, including Thailand, Lao PDR, Vietnam, Korea and the Philippines [1,2,5,7,10,15], with a high incidence of mixed infections involving small liver trematodes and other minute intestinal trematodes [16,17]. The distribution of trematodes requires specific suitable ecological conditions, typically involving certain water resources such as those located in agricultural areas as well as rivers and irrigation canals.…”

Heterophyid trematodes recovered from people residing along the Boseong River, South Korea

“…and C. sinensis are morphologically differentiated with difficulty by the shape and appearance of eggs within the size range of 28-36 m in length and 16-20 m in width (Chai and Lee, 2002;Lee et al, 2012). In this study, ovoid eggs with an attenuated anterior end and an apparent operculum equipped with shoulder rims were regarded as C. sinensis eggs, whereas elliptical eggs without an attenuated end and with an inconspicuous operculum without shoulders were considered as Metagonimus spp.…”

“…The endemic areas of C. sinensis are scattered along five major rivers, including Nakdong, Sumjin, Yeongsan, Gum, and Han Rivers (Seo et al, 1981). Unless adult flukes are recovered from people in endemic areas, it is difficult to diagnose each trematode infection because of morphologic similarities between the eggs of fish-borne trematodes (Chai and Lee, 2002;Lee et al, 2012).…”