Molecular identification of Ascaris lumbricoides and Ascaris suum recovered from humans and pigs in Thailand,Lao PDR,and Myanmar

Parasitology Research - Ascaris lumbricoides is the largest roundworm known from the human intestine while Ascaris suum is an internal parasite of pigs. Ascariasis, caused by Ascaris lumbricoides,...     

Current Status of Human Hookworm Infections,Ascariasis, Trichuriasis,Schistosomiasis Mekongi and Other Trematodiases in Lao People's Democratic Republic

Soil-transmitted helminth (STH) infections, and schistosomiasis and other trematodiases often have a high prevalence in developing countries. Here, we present updated information on the prevalence of these parasites in the Lao People''s Democratic Republic (Lao PDR) in 2012, arising from the annual national helminthiasis survey. Fecal specimens were collected from 8,610 inhabitants of 12 provinces and one municipality (Bokeo, Houaphan, Luang Namtha, Luang Prabang, Oudomxay, and Phongsaly Provinces from northern Lao PDR; Bolikhamxay and Xieng Khouang Provinces and Vientiane Municipality from the central part of the country; and Attapeu, Champasak, Saravan, and Sekong Provinces from southern Lao PDR). The overall prevalence of three major STHs, Ascaris lumbricoides, Trichuris trichiura, and hookworms (Necator americanus and Ancylostoma duodenale) were 11.6%, 8.5%, and 25.0%, respectively. Prevalence of Schistosoma mekongi infection was 0.1%, and of miscellaneous trematodiases (including opisthorchiasis) was 14.0%. Clearly, the nationwide parasite control project is still necessary to reduce morbidity caused by helminthic diseases.Three major soil-transmitted helminths (STHs), i.e., roundworms (Ascaris lumbricoides), whipworms (Trichuris trichiura), and hookworms (Necator americanus and Ancylostoma duodenale) are important public health problems, mostly impacting the health of children in several countries of the Americas, sub-Saharan Africa, China, and East and Southeast Asia, including Lao People''s Democratic Republic (Lao PDR).^1–3 Ascaris lumbricoides is estimated to infect 1.221 billion people globally, T. trichiura 795 million, and hookworms, 740 million globally.¹ The blood fluke, Schistosoma mekongi, occurs in communities along the Mekong River in Cambodia and Lao PDR,⁴ causing intestinal and hepatosplenic disease.^5,6 Many other trematode species can also infect people in Lao PDR. These include the highly pathogenic liver fluke, Opisthorchis viverrini, heterophyids such as Haplorchis taichui, and lecithodendriids such as Phaneropsolus bonnei, and Prosthodendrium molenkampi.⁷ To help planning for improvement of control strategies and evaluation of existing control activities, there was a need to update information on the prevalence and distributions of STHs and schistosomiasis and other trematodes. The information is presented here.During parasitological surveys in 2012, fecal specimens were collected from 8,610 inhabitants located in 12 provinces and one municipality (Bokeo [N = 537], Houaphan [N = 780], Luang Namtha [N = 440], Luang Prabang [N = 157], Oudomxay N = 969], and Phongsaly Provinces [N = 688] from northern Lao PDR; Bolikhamxay [N = 611]and Xieng Khouang [N = 1,143] Provinces and Vientiane Municipality [N = 243] from the central part of the country and Attapeu [N = 645], Champasak [N = 1,076], Saravan [N = 624], and Sekong Provinces [N = 697] from southern Lao PDR) (Figure 1). Sample size calculation was performed by using simple random sampling based on estimated preliminary prevalence data for STHs (Laymanivong and others, unpublished data). A total of 58 villages from 29 districts were randomly selected (2 or 3 districts per province and 2–3 villages per district). Approximately 300 inhabitants, with equal sex ratio, were randomly selected per village. The study was approved by the Ministry of Public Health, Lao PDR. Oral informed consent was obtained from all human adult participants and from parents or legal guardians of minors.Open in a separate windowFigure 1.Percentage prevalence of Ascaris lumbricoides (As), Trichuris trichiura (Tt), hookworm (Hw), Schistosoma mekongi (Sm), and miscellaneous trematodes (including Opisthorchis viverrini) (Mt) in Lao People''s Democratic Republic (PDR) in year 2012.Fecal specimens were examined twice for helminth eggs using the Kato-Katz thick smear technique. Parasitic infections were recorded; numbers of eggs for each helminth species were counted, and intensity of infection was calculated and expressed as eggs per gram of feces (epg). The overall prevalence of A. lumbricoides, T. trichiura, and hookworms were 11.6%, 8.5%, and 25.0%, respectively. The proportion of individuals infected with S. mekongi was 0.1%. Because it is difficult to differentiate eggs of the other trematode species from each other using the Kato-Katz thick smear technique,⁷ such eggs were recorded as miscellaneous trematode eggs. The overall prevalence of flukes producing such eggs was 14.0%. The individual prevalence of parasites in 12 provinces and one municipality are shown in Figure 1. Infections were categorized as light, moderate, or heavy, following previous criteria⁸ and are presented in Supplemental Table. The majority of infections were light. Before the implementation of a 5-year project⁹ supported by Loa PDR-Korea and the World Health Organization (WHO) Regional Office for the Western Pacific on the control of intestinal parasitic diseases for primary school in Lao PDR was commenced in 2000, the baseline data on the high prevalence of intestinal parasitic infections in Lao PDR were 34.9% for A. lumbricoides, 19.1% for hookworm, and 25.8% for T. trichiura.⁹ This study revealed that the prevalence of A. lumbricoides and T. trichiura infections decreased about 70% and parasite loads are also low. This reason could be a result of the good effective approach of a nationwide parasite control project.⁹

Table 1

Prevalences and intensities of Ascaris lumbricoides, Trichuris trichiura, hook worm, Schistosoma mekongi, and miscellaneous trematode infections in LAO PDR in year 2012

Field application and evaluation of a rapid immunochromatographic test for detection of Plasmodium falciparum infection among the inhabitants of Lao PDR

Field application and evaluation of a rapid immunochromatographic test (ICT) for detection of Plasmodium falciparum infection were performed in 13 villages in a southern province of Lao PDR in 1999. More than 2,000 inhabitants, accounting for 61.8% of the total estimated population, were examined. Malaria infection was confirmed in all villages surveyed by ICT and microscopic diagnosis. The positive rates of P. falciparum malaria by microscopy ranged from 9.7% to 59.2% (mean 27.2%), whereas by ICT they were from 11.6% to 64.5% (mean 29.8%). The positive rates by ICT were generally higher in 8 out of 13 villages. However, a significant difference between the positive rates by microscopy and ICT was not observed in all villages. Plasmodium falciparum infection was actually confirmed by microscopy in 84.1% of specimens that tested positive by ICT. The results by ICT were consistent with those of the microscopic diagnosis, the discrepancy of the results was less than 10% (141/2,066). The ICT was falsely-positive in 4.7% and falsely-negative in 2.1% of the test cases. These results showed the efficacy of ICT not only in the diagnosis of the respective cases, but also in the mass-examination in the field.