Episodic positive selection in the Cam734 haplotype and low prevalence of the A144F mutation in Plasmodium falciparum chloroquine resistance transporter gene among Thai isolates

@#Chloroquine resistance transporter of Plasmodium falciparum (PfCRT) is a food vacuolar transmembrane protein that mediates susceptibility of the parasite to chloroquine. A mutation at K76T of the Pfcrt gene is a key determinant for chloroquine resistance phenotype. In the absence of drug pressure, in vitro growth rate of chloroquine-resistance parasites was outcompeted by wild-type parasites unless intragenic compensatory mutations occurred. Chloroquine-resistant P. falciparum bearing the Cam734 haplotype known to circulate in endemic areas of Cambodia bordering Thailand contains 9 mutations in Pfcrt and exhibits both chloroquine resistance and comparable growth rate to the chloroquine-sensitive 3D7 strain. To analyze the evolution of the Cam734 haplotype, codon-based analysis was performed by using the mixed effects model of evolution (MEME), branch-site random effects likelihood (BR-REL) and other related methods. Results revealed that the Cam734 haplotype has evolved distinctively from other known mutant haplotypes including the most common Dd2 haplotype in Southeast Asia. Evidence of episodic positive selection was detected at codon 144, characterized by c.[430G>T; 431C>T] (p.A144F), known to be indispensable for both chloroquine resistance and restoration of growth rate of the parasites. To survey the prevalence of mutations at codons 76 and 144 in Pfcrt among Thai isolates, restriction fragment analysis of 548 P. falciparum isolates collected from six endemic provinces of Thailand during 1991 and 2016 was performed. The 144F Pfcrt mutant was detected in 7 (1.28%) isolates. All Thai isolates analyzed herein harbored a mutation at codon 76 whilst the wild-type parasite was not found. The low prevalence of isolates bearing the mutation 144F in PfCRT could imply little or lack of survival advantage of this mutant in endemic areas of Thailand where the wild-type parasites seem to be absent or extremely rare.

Trichuris vulpis and T. trichiura infections among schoolchildren of a rural community in northwestern Thailand: the possible role of dogs in disease transmission

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Background: Trichuriasis is an important soil-transmitted helminth infection caused by Trichuris trichiura. About one-tenth of the world population may be infected. Incidentally, T. vulpis or dog whipworm has been reported to infect humans based on the egg size. However, an overlapping egg dimension occurs between T. trichiura and T. vulpis leading to the potential for misdiagnosis. Objective: Develope a PCR method to differentiate T. trichiura and T. vulpis eggs in stool samples and to investigate the prevalence of both whipworms in humans and dogs in a rural community in Thailand. Materials and methods: We determined and compared the small subunit ribosomal RNA sequences of both species of whipworms for developing species-specific PCR diagnosis. After validation of the method, we conducted a cross-sectional survey at Ta Song Yang District in Tak Province, northwestern Thailand in 2008. Stool samples were randomly recruited from 80 schoolchildren (36 males, 44 females) and 79 dogs in this community. Results: Fifty-six individuals harbored Trichuris eggs in their stools. The PCR-based diagnosis revealed that 50 cases were infected with T. trichiura and six (10.7%) were co-infected with both T. trichiura and T. vulpis. Although the dimension of Trichuris eggs provided some diagnostic clues for species differentiation, a remarkable variation in the length of these whipworm eggs was observed among samples that could lead to misdiagnosis. Conclusion: Both T. trichiura and T. vulpis eggs were detected in stool samples of dogs that roamed around this community, highlighting the potential reservoir role of dogs in the transmission of both human and dog whipworms in this population.

The merozoite surface protein 2 (MSP2) gene of Plasmodium falciparum from a Thai isolate.

The merozoite surface protein 2 (MSP2) of Plasmodium falciparum was a malaria vaccine candidate. The gene encoding MSP2 of a Thai isolate was amplified by polymerase chain reaction followed by subcloning into a phagemid vector and sequencing. Sequence alignment with other previously published sequences revealed that the MSP2 allele in this isolate belonged to FC27 allelic family. The central variable sequence of the MSP2 allele in this study was related to an allele from Indonesia. The flanking sequences of the variable region were highly conserved.

Cryptosporidiosis among orphanage children in Thailand: a one year prospective study.

The prevalence of cryptosporidiosis and other parasitic infections was studied among the orphanage children in Nonthaburi province, Thailand, during May 1986--April 1987. Cryptosporidium oocysts were detected in fecal specimens of 22 out of 303 diarrheal cases (7.3%) by using a modified cold Kinyoun acid-fast technique. None were found among 513 children without diarrhea. Most of the cryptosporidiosis cases were those under 3 years old. The duration of diarrhea in 20 cases varied from 1 to 25 days (mean = 6.6 days). All cases recovered uneventfully without repeated infection. No sexual preponderance was found. Most of the infections were documented during March to June when both temperature and rainfall were high. It was also noted that these children had high rates of other parasitic infections, 38.1% of the total population. Thus, cryptosporidiosis was not uncommon among children with diarrhea and could be detected almost throughout the year.

Cryptosporidiosis: report of a case with life-threatening diarrhea.

A case of life-threatening chronic diarrhea, caused by Cryptosporidium spp., was reported. The patient was a seven month old boy from an orphanage suffering from voluminous watery diarrhea, fever and vomiting three days before admission. He presented with severe dehydration and severe hypokalemia. Numerous cryptosporidial oocysts were detected in the stools without other enteropathogens. Although co-trimoxazole and gentamicin were administered in the first week of illness, the diarrheal symptom was still persistent. At the end of the third week, spontaneous remission was observed. The overall diarrheal period lasted twenty-five days. In this case, cryptosporidiosis manifested as severe chronic diarrhea in the immunocompetent and supportive management was very important because an effective drug is not available at present.