First molecular identification and genetic diversity of Strongyloides stercoralis and Strongyloides fuelleborni in human communities having contact with long-tailed macaques in Thailand.

The parasitic nematodes, Strongyloides stercoralis and Strongyloides fuelleborni, can infect humans and non-human primates. We amplified and sequenced a portion of the 18S ribosomal RNA gene (rRNA) and of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene of Strongyloides from humans in the study area in Thailand, where people have frequent contact with long-tailed macaques. Fresh stool samples were obtained from 213 people and were examined using the agar plate culture method. The overall prevalence of Strongyloides infection was 8.92% (19/213). From a total of 19 worms (one per infected person), 18 adult males had 18S rRNA sequences identical with that of S. stercoralis and one adult female had a sequence almost identical with that of S. fuelleborni. A median-joining network of cox1 sequences revealed nine new haplotypes from S. stercoralis, and an overall haplotype diversity (Hd) of 0.9309. The single haplotype of S. fuelleborni was also new and contributed to an overall haplotype diversity for that species of 0.9842. This is the first molecular identification of S. stercoralis and S. fuelleborni in a human community having contact with long-tailed macaques in Thailand. It is also the first report of S. fuelleborni infecting a human in Thailand.

Thelazia callipaeda: a human case report.

We report a rare case of human thelaziasis. A 31-year-old man from Nakhon Pathom, Thailand presented to the hospital with a foreign body sensation in and excessive lacrimation from the right eye for one week. His visual acuity was normal. He gave a history of a fly flying around his face; he then rubbed it against his right eye. Five adult worms were collected from the right eye. Two were removed by the patients and three were removed on the ward, using a small cotton swab, from the conjunctival sac. All five worms were identified morphologically as Thelazia callipaeda. The patient became free of symptoms after the fifth worm was removed.

Discovery of Opisthorchis viverrini metacercariae in freshwater fish in southern Cambodia.

Small liver flukes, Clonorchis sinensis and Opisthorchis viverini, are fish-borne trematodes (FBTs) causing significant public health problems in Asia. While C. sinensis is distributing mainly in far east Asia, O. viverini is distributing in Indochina peninsula. Recently, however, the geographical distributions of those small liver flukes were proven to be far wider than expected. Nevertheless, little is known about the epidemiology of small liver flukes in Cambodia. The present study is, therefore, aimed at clarifying the status of small liver fluke infections in various species of freshwater fish in southern Cambodia. A total of 1479 freshwater fish, 1316 (89%) comprised of 20 different species of the cyprinoid family and 163 (11%) belonging to 8 families of non-cyprinoids, were collected during May 2007 and February 2008, and the presence of small liver fluke metacercariae was examined by the compression method. Small liver fluke metacercariae were found in 10 species of cyprinoids with the infection rate ranging 2.1-66.7% and the mean intensity of infection of 1.0-15.0 (range: 1-65). For the speciation, adult worms were obtained by experimental infection in hamsters. The small liver fluke found in this study were identified as Opisthorchis viverrini by the morphological features of adult worms, and this identification was confirmed by partial COI sequencing of the metacercariae.

Parasitological monitoring of helminth control program in Northern Thailand.

Nan Province, located in northern Thailand, is hyperendemic for parasite infections; the helminthic infection rate in 1,010 schoolchildren was 60.0% in 2001. Mass anthelmintic chemotherapy has been conducted with schoolchildren, and selective treatment has been given to people in the community, from 2002. The modified cellophane thick smear method was used to examine the prevalence and intensity of helminth infections in schoolchildren and community people once a year during the period 2002-2004. The prevalence of helminth infections decreased slowly from 60.0 to 40.3% in schoolchildren and from 70.8 to 60.0% in the older age population. Three parasite species were common: hookworm, Ascaris and Haplorchis, an intestinal trematode. Hookworm presented throughout the whole district. Ascaris infection occurred at high rates in some villages, while in some villages none was found. The villages where Ascaris infection was nil had high rates of Haplorchis infection, and vice versa. Most hookworm and Trichuris infections were of light intensity. Heavy intensity infection was found in 12.8-18.1% of Ascaris cases examined. Parasite infection rates in Chaloem Phra Kiat District can be classified as low prevalence.

The potential usefulness of the modified Kato thick smear technique in the detection of intestinal sarcocystosis during field surveys.

A total of 479 stool specimens were collected from rural communities of Ubon Ratchathani Province, Thailand and examined by two techniques: the modified Kato thick smear and the direct smear. The prevalence of Opisthorchis viverrini (14.8%), hookworm (10.2%), Sarcocystis spp (4.6%), Taenia spp (2.9%), Strongyloides stercoralis (2.1%), Giardia lamblia (1.2%), Echinostoma spp (0.6%), Ascaris lumbricoides (0.4%), Entamoeba histolytica (0.2%), Chilomastix mesnili (0.2%) and Endolimax nana (0.2%) were determined. The morphology of the Sarcocystis spp sporocysts examined by both procedures looked similar and was found to be easily recognizable. Among these specimens, 22 cases (4.6%) were positive for Sarcocystis infection detected by the modified Kato technique, whereas only one case (0.2%) was detected by both techniques. These differences were found to be statistically significant (p < 0.05), indicating that the modified Kato technique was decidedly more sensitive than the direct smear procedure in identifying Sarcocystis infection. An epidemiological survey was conducted in Khon Kaen Province involving 1124 stool samples using the modified Kato technique. The greatest frequency was Opisthorchis viverrini at 32.0% while the second highest was Sarcocystis spp at 8.0%. The prevalences of hookworm, Echinostoma spp, Taenia spp, Trichuris trichiura and Enterobius vermicularis were 2.7, 2.1, 1.0, 0.2 and 0.2%, respectively. Other than opisthorchiasis, northeastern Thailand may be an endemic area for sarcocystosis. This is the first report of the applicability and potential usefulness of the Kato thick smear technique for the diagnosis of Sarcocystis infection in a field survey.

Cyclospora cayetanensis: oocyst characteristics and excystation.

In Thailand in 1999-2000, Cyclospora oocysts from two HIV-infected patients and one patient with prolonged diarrhea were detected by formalin-ether concentration technique. Sporulation was performed by mixing stool samples in 2.5% potassium dichromate solution, sporulated oocysts were then treated with various solutions before mechanical rupturing in order to establish excystation, fewer than 10% of the sporulated oocysts could be excysted. Our techniques provided more details of the characteristic appearance of sporocysts and sporozoites within the oocysts (DMSO-modified acid-fast technique with our modification).