In vitro atovaquone/proguanil susceptibility and characterization of the cytochrome b gene of Plasmodium falciparum from different endemic regions of Thailand

<p>Abstract</p> <p>Background</p> <p>The emergence of <it>Plasmodium falciparum </it>resistant to most currently used antimalarial drugs is the major problem in malaria control along the Thai-Myanmar and Thai-Cambodia borders. Although artemisinin-based combination therapy has been recommended for the treatment of multidrug-resistant falciparum malaria, these combinations are not available for some people, such as travelers from North America. A fixed-dose combination of atovaquone and proguanil (Malarone) has been proved to be effective for the treatment and prophylaxis of malaria which is already approved by countries in North America and Europe. Determination of the phenotypes and genotypes related to atovaquone/proguanil response in Thai isolates of <it>P. falciparum </it>will be useful for rationale drug use. The main purpose of this study was to explore the <it>in vitro </it>atovaquone/proguanil susceptibility of recently adapted Thai isolates of <it>P. falciparum</it>. Genotypic characterization of the <it>cytb </it>gene of these isolates was also determined since it has been reported that point mutations, particularly codon 268 in the cytochrome b gene (<it>cytb</it>) have been linked to atovaquone/proguanil treatment failure.</p> <p>Methods</p> <p>Eighty three <it>P. falciparum </it>isolates collected during 1998 to 2005 from four different multidrug resistance areas of Thailand were determined for the <it>in vitro </it>atovaquone/proguanil susceptibilities using radioisotopic assay. Mutations in the <it>cytb </it>gene were determined by PCR-RFLP and sequence analysis.</p> <p>Results</p> <p>The mean atovaquone and proguanil IC₅₀was 3.4 nM and 36.5 μM, respectively. All 83 Thai isolates were atovaquone sensitive. None of the 83 isolates contained the mutations at codon 268 of the <it>cytb </it>gene. DNA sequencing of the <it>cytb </it>gene of 20 parasite isolates showed no other mutations.</p> <p>Conclusion</p> <p>In agreement with a recent efficacy study of atovaquone/proguanil, the present information indicates that atovaquone/proguanil can be one of the drugs of choice for the treatment and prophylaxis of multidrug-resistant falciparum malaria in Thailand.</p

Suppression of Plasmodium falciparum by serum collected from a case of Plasmodium vivax infection.

BACKGROUND: It has frequently been reported that Plasmodium vivax suppressed Plasmodium falciparum and ameliorated disease severity in patients infected with these two species simultaneously. The authors investigate the hypothesis that immunological responses stimulated by P. vivax may play a role in suppressing co-infecting P. falciparum. METHODS: Sera, taken sequentially from one of the authors (YN) during experimental infection with P. vivax, were added to in vitro cultures of P. falciparum. Cross-reactive antibodies against P. falciparum antigens, and cytokines were measured in the sera. RESULTS: Significant growth inhibitory effects upon P. falciparum cultures (maximally 68% inhibition as compared to pre-illness average) were observed in the sera collected during an acute episode. Such inhibitory effects showed a strong positive temporal correlation with cross-reactive antibodies, especially IgM against P. falciparum schizont extract and, to a lesser degree, IgM against Merozoite Surface Protein (MSP)-119. Interleukin (IL)-12 showed the highest temporal correlation with P. vivax parasitaemia and with body temperatures in the volunteer. CONCLUSION: These results suggest the involvement by cross-reactive antibodies, especially IgM, in the interplay between plasmodial species. IL-12 may be one of direct mediators of fever induction by rupturing P. vivax schizonts, at least in some subjects. Future studies, preferably of epidemiological design, to reveal the association between cross-reactive IgM and cross-plasmodial interaction, are warranted

Survey of laboratory practices for diagnosis of fungal infection in seven Asian countries: An Asia Fungal Working Group (AFWG) initiative

An online survey of mycology laboratories in seven Asian countries was conducted to assess the status, competence, and services available. Country representatives from the Asia Fungal Working Group (AFWG) contacted as many laboratories performing mycology diagnosis as possible in their respective countries, requesting that the laboratory heads complete the online survey. In total, 241 laboratories responded, including 71 in China, 104 in India, 11 in Indonesia, 26 in the Philippines, four in Singapore, 18 in Taiwan, and seven in Thailand. Overall, 129/241 (53.5%) surveyed mycology laboratories operate as separate designated mycology laboratories, 75/241 (31.1%) conduct regular formal staff training, 103/241 (42.7%) are accredited, and 88/157 (56.1%) participate in external quality assurance scheme (EQAS) programs. Microscopy and culture methods are available in nearly all laboratories, although few perform DNA sequencing (37/219; 16.9%) or use matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS) (27/219; 12.3%) for isolate identification. Antifungal susceptibility testing is performed in 142/241 (58.9%) laboratories, mainly for yeasts. The most commonly performed nonculture diagnostic is cryptococcal antigen testing (66 laboratories), followed by galactomannan testing (55), polymerase chain reaction (PCR) diagnosis (37), and beta-D-glucan testing (24). Therapeutic drug monitoring is conducted in 21 laboratories. There is almost no access to advanced diagnostic tests, like galactomannan, β-D-glucan, and PCR, in the surveyed laboratories in Indonesia, the Philippines, and Thailand. These results highlight the need for development of quality laboratories, accreditation and training of manpower in existing laboratories, and access to advanced non–culture-based diagnostic tests to facilitate the diagnosis of fungal infections in Asia

ama1 Genes of Sympatric Plasmodium vivax and P. falciparum from Venezuela Differ Significantly in Genetic Diversity and Recombination Frequency

BACKGROUND: We present the first population genetic analysis of homologous loci from two sympatric human malaria parasite populations sharing the same human hosts, using full-length sequences of ama1 genes from Plasmodium vivax and P. falciparum collected in the Venezuelan Amazon. METHODOLOGY/PRINCIPAL FINDINGS: Significant differences between the two species were found in genetic diversity at the ama1 locus, with 18 distinct haplotypes identified among the 73 Pvama1 sequences obtained, compared to 6 unique haplotypes from 30 Pfama1 sequences, giving overall diversity estimates of h = 0.9091, and h = 0.538 respectively. Levels of recombination were also found to differ between the species, with P. falciparum exhibiting very little recombination across the 1.77 kb sequence. In contrast, analysis of patterns of nucleotide substitutions provided evidence that polymorphisms in the ama1 gene of both species are maintained by balancing selection, particularly in domain I. The two distinct population structures observed are unlikely to result from different selective forces acting upon the two species, which share both human and mosquito hosts in this setting. Rather, the highly structured P. falciparum population appears to be the result of a population bottleneck, while the much less structured P. vivax population is likely to be derived from an ancient pool of diversity, as reflected in a larger estimate of effective population size for this species. Greatly reduced mosquito transmission in 1997, due to low rainfall prior to the second survey, was associated with far fewer P. falciparum infections, but an increase in P. vivax infections, probably due to hypnozoite activation. CONCLUSIONS/SIGNIFICANCE: The relevance of these findings to putative competitive interactions between these two important human pathogen species is discussed. These results highlight the need for future control interventions to employ strategies targeting each of the parasite species present in endemic areas

Clonal diversity of the glutamate dehydrogenase gene in Giardia duodenalis from Thai Isolates: evidence of genetic exchange or Mixed Infections?

Background: The glutamate dehydrogenase gene (gdh) is one of the most popular and useful genetic markers for the genotypic analysis of Giardia duodenalis (syn. G. lamblia, G. intestinalis), the protozoan that widely causes enteric disease in humans. To determine the distribution of genotypes of G. duodenalis in Thai populations and to investigate the extent of sequence variation at this locus, 42 fecal samples were collected from 3 regions of Thailand i.e., Central, Northern, and Eastern regions. All specimens were analyzed using PCR-based genotyping and recombinant subcloning methods. Results: The results showed that the prevalence of assemblages A and B among these populations was approximately equal, 20 (47.6%) and 22 (52.4%), respectively. Sequence analysis revealed that the nucleotide diversity of assemblage B was significantly greater than that in assemblage A. Among all assemblage B positive specimens, the allelic sequence divergence within isolates was detected. Nine isolates showed mixed alleles, ranged from three to nine distinct alleles per isolate. Statistical analysis demonstrated the occurrence of genetic recombination within subassemblages BIII and BIV was likely. Conclusion: This study supports increasing evidence that G. duodenalis has the potential for genetic exchange