Sero-epidemiological survey of gnathostomiasis in Lao PDR

While human gnathostomiasis cases have been reported sporadically in Lao PDR since 1975, little is known about the disease in this country. We aimed to investigate sero-prevalence of gnathostomiasis and Gnathostoma species in Lao PDR. One village each in the north, central and south regions of Lao PDR was selected as the study sites. Overall, 125 (29.8%) of 420 sera from the randomly selected participants were sero-positive by immunoblot technique, with anti-Gnathostoma IgG antibody against the 24 kDa fraction. The sero-prevalence was high in the central (47.1%) and south (38.6%), but low (3.6%) in the north. Risk factor analyses revealed that the consumption of raw/undercooked fish was significantly associated with Gnathostoma sero-positivity (95% CI 1.05–17.05, P = 0.042). The sero-positivity significantly increased with the age of the participants. Several fish, swamp eels, and frogs collected from central and southern Lao were infected with G. spinigerum advanced 3rd-stage larvae. Channa limbata (red-tailed snakehead fish) was identified as a natural second intermediate host of G. spinigerum. Eggs of G. spinigerum were found in dog feces collected in the south. Gnathostomiasis is endemic in central and southern Laos, so that preventive measures should be introduced for people living in these regions.     

Prevalence of Helminthic Infections among Inhabitants of Lao PDR

The prevalence of helminthic infections was surveyed on a total of 6,178 residents (males 2,549 and females 3,629) in 102 villages of 9 provinces in Lao PDR between 2007 and 2011 under the project of Korea-Laos Collaborative Project for Control of Foodborne Trematode Infections in Lao PDR. Fecal specimens were collected and examined by the Kato-Katz thick smear and Stoll''s egg counting techniques. The overall liver/intestinal helminth egg positive rate was 71.9% with a single or mixed infections with Opisthorchis viverrini and minute intestinal flukes (Ov/MIF), Ascaris lumbricoides, hookworms, Trichuris trichiura, Trichostrongylus sp., echinostomes, Taenia spp., and others. Ov/MIF revealed the highest prevalence (55.6%) followed by hookworms (27.8%) and T. trichiura (6.5%). The endemic regions with the highest prevalence of Ov/MIF were Savannakhet, Khammouane, Vientiane (Nam Ngum), Champasak (Khong Island), and Saravane Province. High prevalences of A. lumbricoides (33.8%), hookworms (47.8%), and T. trichiura (32.6%) were observed in Phongsaly, Luang Prabang, and Vientiane (Nam Ngum) areas, respectively. The results of this study highlight helminth parasites of current public health significance in different areas of Lao PDR.     

Fishborne Trematode Metacercariae in Luang Prabang,Khammouane, and Saravane Province,Lao PDR

Fishborne trematode (FBT) metacercariae were investigated in fish from 3 Provinces of Lao PDR. Total 242 freshwater fish of 40 species were collected in local markets of Luang Prabang (59 fish of 16 species), Khammouane (81 fish of 19 species), and Saravane (97 fish of 14 species), and each of them was examined by artificial digestion method. Four species of metacercariae (Opisthorchis viverrini, Haplorchis taichui, Haplorchis yokogawai, and Centrocestus formosanus) were detected. O. viverrini was detected in 35 fish (14.5%), and their density was 252 per infected fish (Luang Prabang, 88 metacercariae in 5 fish; Khammouane, 187 in 6 fish; Saravane, 303 in 24 fish). H. taichui was found in 102 fish (42.1%), and their density was 485 per infected fish (Luang Prabang, 260 metacercariae in 38 fish; Khammouane, 1,084 in 23 fish; Saravane, 359 in 41 fish). H. yokogawai was detected in 92 fish (38.0%), and their density was 222 per infected fish (Luang Prabang, 362 metacercariae in 17 fish; Khammouane, 126 in 20 fish; Saravane, 214 in 55 fish). Metacercariae of C. formosanus were found in 8 fish (3.3%), and their density was 3 per infected fish. In the present study, it has been confirmed that FBT metacercariae, in particular, H. taichui, H. yokogawai, and O. viverrini, are highly prevalent in fish from Luang Prabang, Khammouane, and Saravane Province, Lao PDR.     

Echinostome Flukes Receovered from Humans in Khammouane Province, Lao PDR

Echinostome eggs were detected in 22 (1.1%) of 2,074 people residing in riparian villages along the Mekong River in Khammouane Province, Lao PDR. In order to recover the adult flukes, 9 persons were treated with praziquantel and purged with magnesium salts. A total of 55 echinostome specimens (4 species) were recovered from the 9 persons. Echinostoma revolutum (8 specimens) was recovered from 3 persons, Artyfechinostomum malayanum (8 specimens) was from 2 persons, Echinochasmus japonicus (33 specimens) was from 7 persons, and Euparyphium sp. (6 specimens) was from 1 person. In Lao PDR, only human infections with E. japonicus were previously known. Therefore, the present study describes human infections with E. revolutum, A. malayanum, and Euparyphium sp. for the first time in Lao PDR. These results indicate that the surveyed villages of Khammouane Province, Lao PDR are low-grade endemic foci of echinostomiasis.     

Malaria education from school to community in Oudomxay province, Lao PDR

School-based malaria education has been shown to be effective for improving the knowledge, attitudes, and practices of school children toward malaria control. However, little has been reported about the effect of such education on communities in developing countries. To evaluate the influence of school-based malaria education on the knowledge, attitudes, and practices of people in the community toward malaria, we conducted a school-based intervention in Oudomxay province, Lao PDR, and compared scores obtained before and after the intervention. Participants were 130 school children in grades 3-5 at two primary schools, 103 guardians of these children, and 130 married women who did not have children in the target grades. The intervention included presentation of a flipchart at home and a 1-day campaign conducted by the school children and aimed at the community. The flipchart presentation was conducted at villages where school children of both primary schools resided. The 1-day campaign was, however, conducted only at one village. Before and after the intervention, we conducted a questionnaire-based survey of community women that pertained to malaria. Our main finding was that, in married women without children in the target grades, particularly those who were presented with the flipchart and participated in the campaign, the scores of the mean knowledge, attitudes and practices were significantly increased 1 month after the intervention. In conclusion, our results suggest that school children can act as health information messengers from schools to communities for malaria control in Lao PDR.     

High prevalence of liver and intestinal fluke infections among residents of Savannakhet Province in Laos

The prevalence of liver and intestinal fluke infections was surveyed on residents of Savannakhet Province, Laos. Fecal specimens were collected from a total of 981 residents in 4 Mekong riverside villages and examined by the Kato-Katz thick smear technique. The results revealed that the overall helminth egg positive rate was 84.2%, and the positive rate for small trematode eggs, including Opisthorchis viverrini, heterophyids, or lecithodendriids, was 67.1%. To obtain adult flukes, 38 small trematode egg positive cases were treated with a 20-30 mg/kg single dose of praziquantel and purged. Diarrheic stools were then collected from 29 people and searched for helminth parasites using stereomicroscopes. Mixed infections with O. viverrini and 6 kinds of intestinal flukes were found, namely, Haplorchis taichui, Haplorchis pumilio, Haplorchis yokogawai, Prosthodendrium molenkampi, Phaneropsolus bonnei, and echinostomes. The total number of flukes collected was 7,693 specimens (av. no. per treated person; 265.3). The most common species was O. viverrini, followed by H. taichui, P. molenkampi, echinostomes, H. pumilio, P. bonnei, and H. yokogawai. The results indicate that foodborne liver and intestinal fluke infections are prevalent among residents of Savannakhet Province, Laos.     

Current Status of Human Taeniasis in Lao People's Democratic Republic

Human taeniasis was investigated in Lao People''s Democratic Republic (Lao PDR) between 2000 and 2011 as part of the nation''s helminthiasis survey. A total of 55,038 inhabitants, including 29,846 school children, were examined using the Kato-Katz and scotch-tape anal swab method, and morphological observation of adult worms. Molecular identification of Taenia tapeworms was performed by multiplex PCR or DNA sequence analysis of the mitochondrial cox1 gene. Taenia eggs were present at a rate of 1.5% (845/55,038) in the subject population. Adult tapeworms were identified as T. solium or T. saginata by analyzing the collectable stool specimens (n=126). Three specimens identified as T. solium were found in Luang Prabang, while the remaining 123 specimens, which were T. saginata, were found in Bokeo, Bolikhamxay, Champasak, Houaphan, Khammouane, Luang Namta, Luang Prabang, Oudomxay, Phongsaly, Saysomboune, Saravane, Savannakhet, Xayaboury, Xekong, Xieng Khouang Province, and Vientiane Municipality.     

Prevalence of the intestinal flukes Haplorchis taichui and H. yokogawai in a mountainous area of Phongsaly Province, Lao PDR

Phongsaly Province, located in the northernmost area of Lao PDR, was previously suggested to be endemic for the liver fluke Opisthorchis viverrini infection. To confirm, or rule out, this suggestion, the Phonxay village in the Khoua District, Phongsaly Province, was selected for a survey. Ten volunteers (8 men and 2 women aged 31-57 years) who consumed raw freshwater fish and had gastrointestinal troubles were treated with a single dose of praziquantel (40 mg/kg) and pyrantel pamoate (10 mg/kg) and purged with magnesium sulfate to recover any worm parasites. Eight of the 10 volunteers expelled 1 or more species of trematodes, nematodes, or cestodes (worm positive rate; 80%). The worms were morphologically identified as H. taichui (861 worms from 8 people), H. yokogawai (59 from 6 people), Phaneropsolus bonnei (1 from 1 person), Trichostrongylus sp. (2 from 2 people), Ascaris lumbricoides (2 from 1 person), Enterobius vermicularis (11 from 3 people), and Taenia saginata (1 strobila with scolex from 1 person). The results indicate that the mountainous area of Phongsaly Province, Lao PDR, is not endemic for the liver fluke but endemic for intestinal flukes, in particular, Haplorchis taichui and H. yokogawai.     

Infection Status of Zoonotic Trematode Metacercariae in Fishes from Vientiane Municipality and Champasak Province in Lao PDR

The infection status of fishborne zoonotic trematode (FZT) metacercariae was investigated in fishes from 2 localities of Lao PDR. Total 157 freshwater fishes (17 species) were collected in local markets of Vientiane Municipality and Champasak Province in December 2010 and July 2011, and each fish was examined by the artificial digestion method. Total 6 species of FZT metacercariae, i.e., Opisthorchis viverrini, Haplorchis taichui, Haplorchis yokogawai, Haplorchis pumilio, Centrocestus formosanus, and Procerovum varium, were detected in fishes from Vientiane Municipality. The metacercariae of O. viverrini were detected in 50 (49.5%) out of 101 fishes (6 species), and their average number was 154 per fish infected. The remaining 5 species of heterophyid metacercariae were detected in 36.8%, 65.8%, 9.4%, 23.9%, and 5.1% fishes examined, and their average densities were 12, 1,038, 4, 15, and 13 per infected fish, respectively. In fishes from Champasak Province, 3 species of FZT metacercariae, i.e., O. viverrini, H. taichui, and H. yokogawai, were detected. Only 2 O. viverrini metacercariae were found in only 1 Barbonymus schwanefeldi. The metacercariae of H. taichui and H. yokogawai were detected in 60.0% and 50.0% of fishes examined, and their average densities were 47 and 28 per fish infected. By the present study, it has been confirmed that several species of FZT metacercariae are prevalent in fishes from Vientiane Municipality, with P. varium being a new member of FZT in Lao PDR. In comparison, FZT metacercariae are less prevalent in fishes from Champasak Province.     

Discovery of Opisthorchis lobatus (Trematoda: Opisthorchiidae): a new record of small liver flukes in the Greater Mekong Sub-region

Metacercariae, morphologically similar to those of small liver flukes, were found to parasitize red-tailed snakehead fish, Channa limbata, collected from the city of Vientiane, Lao People's Democratic Republic. Adult worms that were recovered from experimentally-infected hamsters showed characteristics distinctly different from Opisthorchis viverrini, but closely similar to Opisthorchis lobatus, which was first reported in poultry (Anas sp.) from Pakistan. The present study aimed to redescribe O. lobatus based on the adult worms recovered from experimentally-infected hamsters. Additionally, it aimed to document the genetic relationships among O. lobatus and other opisthorchiid liver flukes using the mitochondrial cytochrome c oxidase subunit 1 (COI) gene and the internal transcribed spacer 2 (ITS2) region. DNA alignment of the O. lobatus and O. viverrini COI partial sequences (330 bp) showed 3.03% fixed differences (2.72% of amino acids changed) while the ITS2 region (350 bp) indicated a 0.86% difference for nucleotides. Species boundaries between the 2 parasites were determined by neighbor-joining analysis using the molecular sequence data. The phenogram confirmed that O. lobatus was distinctly different from O. viverrini, representing the first reported instance of O. lobatus in the Greater Mekong Sub-region (GMS) and the first record of C. limbata as the second intermediate host of a small liver fluke. Questions regarding human infection and the extent of the geographic distribution of these species should be investigated further.