In order to investigate the epidemiological situation of intestinal parasite infections in Laos, parasitological surveys were carried out on a national scale including 17 provinces and the Vientiane Municipality. A total of 29,846 stool specimens were collected from primary schoolchildren from May 2000 to June 2002 and examined once with the cellophane thick smear technique. The cumulative egg positive rate for intestinal helminths was 61.9%. By species, the rate for Ascaris lumbricoides was 34.9%, hookworm 19.1%, Trichuris trichiura 25.8%, Opisthorchis viverrini 10.9%, Taenia spp. 0.6% and Hymenolepis spp. 0.2%. The northern mountainous regions such as Phongsaly, Huaphan or Saysomboune Province showed a higher prevalence (over 70%) of soil- transmitted helminths. The regions along the Mekong River such as Khammuane, Saravane or Savannakhet Province showed a higher prevalence (over 20%) of fish-borne parasites. On the other hand, Schistosoma mansoni eggs were detected in 1.7% of schoolchildren only in Champassak Province, a previously endemic area. The highest prevalence was noted in Phongsaly Province (96.0%) and the lowest in Bolikhamxay Province (27.5%). An additional small-scale survey by cellophane anal swab detected Enterobius vermicularis eggs in 35.7% of 451 schoolchildren aged 6-8 years in Khammuane, Vientiane, Champassak Province and the Vientiane Municipality. Meanwhile, the mean blood haemoglobin level of hookworm-infected children was not lower than that of children not infected with hookworm, suggesting that nutritional factors are more important than parasite infection per se. Nevertheless, the above results indicate that a nationwide parasite control project is necessary to reduce possible morbidity due to parasitic diseases in the country.

Faecal examinations for helminth eggs were performed on 1869 people from two riverside localities, Vientiane Municipality and Saravane Province, along the Mekong River, Laos. To obtain adult flukes, 42 people positive for small trematode eggs (Opisthorchis viverrini, heterophyid, or lecithodendriid eggs) were treated with a 20-30 mg kg 21 single dose of praziquantel and purged. Diarrhoeic stools were then collected from 36 people (18 in each area) and searched for helminth parasites using stereomicroscopes.

The extracellular tissue penetrating protozoan parasite Entamoeba histolytica has been known to induce host cell apoptosis. However, the intracellular signaling mechanism used by the parasite to trigger apoptosis is poorly understood. In this study, we investigated the roles of reactive oxygen species (ROS), and of MAPKs in the Entamoeba-induced apoptosis of human neutrophils. The neutrophils incubated with live trophozoites of E. histolytica revealed a marked increase of receptor shedding of CD16 as well as phosphatidylserine (PS) externalization on the cell surface. The Entamoeba-induced apoptosis was effectively blocked by pretreatment of cells with diphenyleneiodonium chloride (DPI), a flavoprotein inhibitor of NADPH oxidase. A large amount of intracellular ROS was detected after exposure to viable trophozoites, and the treatment with DPI strongly inhibited the Entamoeba-induced ROS generation. However, a mitochondrial inhibitor rotenone did not attenuate the Entamoeba-induced ROS generation and apoptosis. Although E. histolytica strongly induced activation of ERK1/2 and p38 MAPK in neutrophils, the activation of ERK1/2 was closely associated with ROS-mediated apoptosis. Pretreatment of neutrophils with MEK1 inhibitor PD98059, but not p38 MAPK inhibitor SB202190, prevented Entamoeba-induced apoptosis. Moreover, DPI almost completely inhibited Entamoeba-induced phosphorylation of ERK1/2, but not phosphorylation of p38 MAPK. These results strongly suggest that NADPH oxidase-derived ROS-mediated activation of ERK1/2 is required for the Entamoeba-induced neutrophil apoptosis.

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Eosinophilic leukocytes function in host protection against parasitic worms. In turn, helminthic parasites harbor specific molecules to evade or paralyze eosinophil-associated host immune responses; these molecules facilitate the migration and survival of parasitic helminths in vivo. This competition between eosinophil and worm leads to stable equilibria between them. An understanding of such dynamic host-eosinophil interactions will help us to uncover mechanisms of cross talk between host and parasite in helminth infection. In this review, we examine recent findings regarding the innate immune responses of eosinophils to helminthic parasites, and discuss the implications of these findings in terms of eosinophil-mediated tissue inflammation in helminth infection.