Documented data regarding human taeniasis and cysticercosis, as well as porcine cysticercosis, in Lao PDR, are quite limited. As far as the literature is concerned, human neurocysticercosis cases in Lao PDR have not been clearly demonstrated except for a few anecdotal cases. However, outside of Lao PDR, there had been some neurocysticercosis cases which were considered as the ones acquired in Lao PDR and then immigrated to Australia [6,7]. Another case of human cysticercosis found in the United States which had some possibility related to Lao PDR was a 14-year-old girl with cysticercosis in the eyelid [8]. Before visiting a clinic, she spent 2 years (1971 and 1972) in Vietnam and Laos and showed no evidence of neurocysticercosis except for a metacestode exhibited from the eyelid [8].

As is well recognized, porcine cysticercosis is endemic to Vietnam and Cambodia [1,4]. Quite a number of human taeniasis in Lao PDR has been reported in Vientiane, Khammouane, and Champasak Province between 1989 and 2002 [9-12] via a nationwide survey from 2000 to 2002 [13] and a study of 814 subjects in Saravane Province [14]. The literature background on human taeniases consisted of 9 reports on intestinal helminth infections in Lao PDR since 1989, inclduing the most recent one [15]. The helminth infections reported were ascariasis, trichuriasis, hookworm infections, strongyloidiasis, enterobiasis, opisthorchiasis, schistosomiasis, minute intestinal trematode infections, and taeniasis. However, very little is known about the distribution and prevalence of human cysticercosis and T. solium taeniasis inside Lao PDR. The present study aimed to provide an evidence of the presence of the life cycle of T. solium and also human cysticercosis case(s) in Oudomxay Province, Lao PDR.

For molecular typing of T. solium metacestodes collected from a pig in the same locality of Oudomxay Province (Fig. 1), PCR-amplified fragments of cox1 were directly sequenced. The primer-walking method was employed to obtain the direct sequences for each of the amplified fragments. Cyclic sequencing from both ends of the fragments was performed using the Big-Dye Terminator sequencing kit (Applied Biosystems, Carlsbad, California, USA) and the reaction products were electrophoresed on an automated DNA sequencer (model 3730KL) (Applied Biosystems). The sequences were assembled and aligned using the BioEdit program (version 5.0.6, BIOSOFT) (Ferguson, Missouri, USA). BLAST searches were used to identify the sequenced regions through comparison with Taenia sequences that had been deposited in the GenBank database. Specifically, we identified Taenia tapeworm specimens by comparison with cox1 nucleotide sequences of T. solium (GenBank no. AB086256), T. saginata (GenBank no. AY684274), and T. asiatica (GenBank no. AF445798). PCR was performed for all specimens as described previously [16].

A male patient with neurocysticercosis was identified in Montai Village, Xay District, Oudomxay Province, Lao PDR while the author's group was visiting the place for a helminthological survey in February 2004. He visited our survey team and gave a history of diagnosis by CT scan in Thailand after an onset of epileptic seizure in 1993 (Fig. 2A). After treatment with albendazole (15 mg/kg, 3 times per day for 7 days, with prednisolone), he was followed up by CT scan 3 years later in Lao PDR and minimized calcified lesions were found. Three of his family members and relatives had the same or similar symptoms, such as headache. One of their favorite foods was chopped pork wrapped with banana leaf (Sommou). Serological diagnosis of cysticercosis was conducted on his family members (n=8) using ELISA. The serum antibody levels in patients with Taenia tapeworm infections were quantified by micro-ELISA. T. solium metacestode antibodies were detected in sera collected from patients, with relative antibody levels in mean absorbance and SD of 0.20±0.04 or higher. Serum samples from 5 people (0.08±0.1) and 3 people (0.25±0.03) displayed significant levels of reactivity with T. solium metacestode antigen. All of them were subjected to coprological examinations by the Kato-Katz method for Taenia eggs but turned out to be negative in all. Further CT scan study was not implemented and subcutaneous nodules were all negative.

A pig was found by our team infected with T. solium metacestodes showing rostellar hooklets (more than 2,000 cysticerci in the whole body) upon slaughter in February 2004, in the same locality of the patient (Fig. 2B). According to the data from the government veterinarian of the Oudomxay Office of Agriculture, Forestry, Livestock, and Fisheries in Xay District, the prevalence of cysticerci-infected animals between February 2003 to October 2004 was 0.6% (46/7,826) in pigs and 3.1% (44/1,437) in cattle (Table 1). The most prevalent areas for cysticerci infection in pigs were Beng (Thameun, Namet, Napa), Namo (Nathong, Nasavang, Ban Khouang), and La (Parkla Lack) villages.

Molecular identification of the cysticerci from pigs on the basis of the DNA sequence corresponding to position 90-530 of the cox1 gene (440 bp) showed 100% similarity to the reference sequence of T. solium (GenBank no. AB086256) and genotypically they were identified as "Asian type" T. solium.

The present study suggested strongly that the life cycle of T. solium is maintained in the surveyed village of Xay District, Oudomxay Province, Lao PDR causing a substantial number of human cysticercosis patients, including neurocysticercosis. Regarding adult tapeworm recovery in various localities of Lao PDR, only 3 among the total 126 strobila recovered from people were T. solium (123 were T. saginata), and all 3 specimens of T. solium were from Luang Prabang Province, which is located just nearby the Oudomxay Province [15]. Hence, it is presumed that the life cycle of T. solium may exist in the northern mountainous areas of Lao PDR, whereas T. saginata is distributed in almost all areas of Lao PDR, i.e., Bokeo, Bolikhamxay, Champasak, Houaphan, Khammouane, Luang Namta, Luang Prabang, Oudomxay, Phongsaly, Saysomboune, Saravane, Savannakhet, Xayaboury, Xe Kong, Xieng Khouang, and Vientiane Municipality [15].

Risk factors for T. solium taeniasis and cysticercosis in Lao PDR include consumption of raw pork and using human feces to fertilize vegetable gardens. The habit of eating raw pork is common in the northern highlands in Vietnam [3] and also in the northern provinces of Lao PDR. Porcine cysticercosis has been identified in pigs in northern Vietnam, primarily through slaughterhouse reports, but these have indicated low infection rates [2]. Although porcine cysticercosis has been said to be present in Cambodia and Lao PDR, the data on the prevalence are rarely available. The present case of neurocysticercosis found in Oudomxay Province was considered to have been infected indigenously in Lao PDR considering the presence of a measled pig at the same locality as well as the survey report evidenced T. solium [15]. The molecular genotyping of the metacestode detected from a pig in this study, as revealed by DNA sequencing of the mitochondrial cox1 gene, indicated that they were identical with the "Asian type T. solium".