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

Box plots of atovaquone and proguanil ICof parasite isolates collected from different endemic areas

<p><b>Copyright information:</b></p><p>Taken from "atovaquone/proguanil susceptibility and characterization of the gene of from different endemic regions of Thailand"</p><p>http://www.malariajournal.com/content/7/1/23</p><p>Malaria Journal 2008;7():23-23.</p><p>Published online 28 Jan 2008</p><p>PMCID:PMC2265725.</p><p></p

Genotypic Study of Pneumocystis jirovecii in Human Immunodeficiency Virus-Positive Patients in Thailand

Pneumocystis jirovecii is one of the common opportunistic infections in human immunodeficiency virus (HIV)-infected patients in Thailand. Information regarding genotypic and epidemiological of this organism in Thai patients is not available. We analyzed the genotypes of 28 P. jirovecii-positive specimens from bronchoalveolar lavage and sputum samples from HIV-infected Thai patients based on nucleotide variations of the internal transcribed spacer regions 1 and 2 of the rRNA gene. Thirteen genotypes were the same as previously reported outside Thailand. Ten genotypes, which included Bp, Er, Eq, Ic, Ir, Ip, Rc, Rp, Qb, and Qq, were new. Ir and Rp were unique and dominant types observed in HIV-infected Thai patients. Thirteen specimens (46.4%) were infected with a single type of P. jirovecii, and fifteen (53.6%) were mixed infections. These differences may be used as genotypic markers for studying the epidemiology and transmission of P. jirovecii in the Thai population

The primary structure of a Plasmodium falciparum polypeptide related to heat shock proteins

A cDNA library constructed from ring-stage RNA isolated from Plasmodium falciparum FCR-3/Gambia was screened with immune human serum and two related positive clones were isolated. Nucleotide sequence analysis of these recombinant clones revealed an open translational reading frame for 681 amino acids with a calculated molecular weight of 74.3 kDa. The deduced amino acid sequence of the polypeptide shows extensive homology to several heat shock proteins (hsp) which have been described. Northern and Southern hybridization analysis indicates that P. falciparum has a second gene which shares common sequences with the hsp gene described in this study