Prevention of Plasmodium vivax malaria recurrence: Efficacy of the standard total dose of primaquine administered over 3 days

Background

The standard total dose (STD) of primaquine to prevent Plasmodium vivax recurrence is 0.25 mg/kg day administered over 14 days (STD-14). We evaluated, in an endemic zone of Colombia, the anti-recurrence efficacy of the STD dose administered over 3 and 14 days, and of sub-STD dose administered over 3 days (71%STD-3, 50%STD-3).

Methods

A controlled clinical trial was carried out with 188 subjects allocated into one of four treatment groups: STD-14, STD-3, 71%STD-3, 50%STD-3.

Results

Recurrences during the 120 days of follow-up were 15% in STD-14, and 57% in STD-3. Treatment with 71%STD-3 and 50%STD-3 resulted in recurrence in >48% subjects within 120 days after the primary episode. High daily doses (1.17 mg/kg day) were well tolerated.

Conclusions

(a) The standard dose and regimen (STD-14) of primaquine to prevent P. vivax relapse is recommended. The administration of the same dose over 3 days (STD-3) should be avoided; (b) doses lower than the STD doses administered over 3 days are ineffective in preventing relapse.     

Prevalence and risk factors associated to pruritus in Plasmodium vivax patients using chloroquine in the Brazilian Amazon

Chloroquine-induced pruritus has been described as a common adverse event in African patients being treated for Plasmodium falciparum malaria, and has been associated with treatment discontinuation in this setting. In Latin America, where Plasmodium vivax is the most common species causing malaria and chloroquine is still used as the first-line schizonticidal for treating this parasite infection, there are no reports on chloroquine-induced pruritus. This study aimed to estimate the frequency of pruritus and associated risk factors in P. vivax-infected patients treated with chloroquine in a reference centre in the Brazilian Amazon. In this cross-sectional study, patients who were prescribed with chloroquine for the treatment of microscopy-confirmed P. vivax infection in the past five days were actively asked about the occurrence of any level of pruritus and potential risk factors were investigated. Univariable and multivariable logistic regression was performed for the analysis of possible risk factors in two sets of patients: (1) all the patients interviewed and (2) restricted to patients with previous use of chloroquine. Among the 510 patients interviewed, 20.4% (95%CI: 16.9–23.9%) developed any level of pruritus during treatment with chloroquine. Most episodes of pruritus occurred during the first two days of treatment and the most common location was hands and feet. In multivariate analysis performed in the entire population, the only risk factors independently associated to pruritus were allergy history (adjusted odds ratio [AOR]: 1.83; 95%CI 1.02–3.31; p = 0.044) and high parasitaemia (AOR: 1.96: 95%CI 1.22–3.13; p = 0.005). In the analysis restricted to the 215 patients with previous use of chloroquine, previous chloroquine-induced pruritus was a strong predictor of pruritus occurrence (AOR: 11.84: 95%CI 3.15–44.47; p < 0.001). Two patients (0.4%) interrupted treatment due to the severity of pruritus. Pruritus is a common adverse event in patients being treated with chloroquine for P. vivax malaria in the Brazilian Amazon. Host–parasite interaction may play a relevant role in the development of pruritus and concurs with the finding of strong association of pruritus with high parasitaemia and allergy history. Patients with previous chloroquine-induced pruritus had a high risk for developing pruritus. Due to its high frequency, this side effect cannot be neglected as it can have major implications on patients’ compliance to treatment hampering elimination efforts in the region.     

Detection of Plasmodium vivax and Plasmodium falciparum DNA in human saliva and urine: Loop-mediated isothermal amplification for malaria diagnosis

This study investigated loop-mediated isothermal amplification (LAMP) detection of Plasmodium falciparum and Plasmodium vivax in urine and saliva of malaria patients. From May to November 2011, 108 febrile patients referred to health centers in Sistan and Baluchestan Province of south-eastern Iran participated in the study. Saliva, urine, and blood samples were analyzed with nested PCR and LAMP targeting the species-specific nucleotide sequence of small subunit ribosomal RNA gene (18S rRNA) of P. falciparum and P. vivax and evaluated for diagnostic accuracy by comparison to blood nested PCR assay. When nested PCR of blood is used as standard, microscopy and nested PCR of saliva and urine samples showed sensitivity of 97.2%, 89.4% and 71% and specificity of 100%, 97.3% and 100%, respectively. LAMP sensitivity of blood, saliva, and urine was 95.8%, 47% and 29%, respectively, whereas LAMP specificity of these samples was 100%. Microscopy and nested PCR of saliva and LAMP of blood were comparable to nested PCR of blood (к = 0.95, 0.83, and 0.94, respectively), but agreement for nested PCR of urine was moderate (к = 0.64) and poor to fair for saliva LAMP and urine LAMP (к = 0.38 and 0.23, respectively). LAMP assay showed low sensitivity for detection of Plasmodium DNA in human saliva and urine compared to results with blood and to nested PCR of blood, saliva, and urine. However, considering the advantages of LAMP technology and of saliva and urine sampling, further research into the method is worthwhile. LAMP protocol and precise preparation protocols need to be defined and optimized for template DNA of saliva and urine.     

Distribution of dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) mutant alleles in Plasmodium vivax isolates from Thailand

The analysis of prevalence and distribution of pvdhfr and pvdhps mutations were performed in 169 samples collected from patients with Plasmodium vivax infection who attended the malaria clinics in the provinces along the three international borders of Thailand (Thai-Myanmar, Thai-Cambodian, and Thai-Malaysian borders). SNP-haplotypes of the pvdhfr at amino acid positions 13, 33, 57, 58, 61, 117, and 173 and of the pvdhps at positions 383 and 553 were examined by nested PCR-RFLP. Significant differences in the prevalence and distribution of pvdhfr and pvdhps combination alleles were observed in P. vivax isolates collected from all the three border areas. The most prevalent combination alleles were triple mutant pvdhfr 57L/58R/117T alleles/double wild-type pvdhps alleles (n = 18), double mutant pvdhfr 58R/117N alleles/double wild-type pvdhps alleles (n = 10), and triple mutant pvdhfr 58R/61M/117N alleles/double wild-type pvdhps alleles (n = 52) or with single mutant pvdhps 383G allele (n = 28), respectively. These information on prevalence and patterns of pvdhfr and pvdhps polymorphisms obtained from the present study suggest the presence of SP pressure on P. vivax isolates in Thailand which could be linked to the introduction of malaria from neighboring countries. Results did not support the application of SP for P. vivax control program in Thailand as well as the neighboring countries.     

A preliminary study on pro- and anti-inflammatory cytokine profiles in Plasmodium vivax malaria patients from central zone of India

The aim of this preliminary study was to investigate the plasma cytokine profiles in a group of patients suffering from Plasmodium vivax malaria during the peak of its transmission season. Plasma samples of 173 P. vivax patients and 34 healthy individuals were analyzed for IFN-γ, TNF-α, IL-10 and IP-10 levels by ELISA. Levels of both pro- and anti-inflammatory cytokines were significantly higher in P. vivax patients compared to controls. Children with P. vivax infection had significantly higher levels of IFN-γ than adults (P = 0.017). Asexual parasitaemia versus TNF-α (r = −0.31, P = 0.01), IL-10 (r = −0.30, P = 0.015) and gametocytaemia versus IFN-γ (r = −0.26; P = 0.034) levels showed significant negative correlation in children compared to adults. The median concentrations of IFN-γ (P = 0.001), IL-10 (P = 0.032) and IP-10 (P ≤ 0.05) were higher in children reported with chills and rigors, whereas in adults only IFN-γ levels was higher (P < 0.0001). The median plasma concentrations of IFN- γ (P = 0.02), IL-10 (P < 0.0001) and IP-10 (P = 0.068) were higher in patients with mild anaemia compared to non-anaemic patients. The results indicated that both pro- and anti-inflammatory cytokine responses are associated with clinical signs of mild anaemia and paroxysm during symptomatic P. vivax malaria in Central India.     

Sequence polymorphisms of Plasmodium vivax tryptophan and alanine rich antigen (PvTARAg55)

Since PvTARAg55 protein (PvTARAg55) of Plasmodium vivax (P. vivax) is expressed during the parasite's sporozoite stage, it was strongly suggested, as a potential candidate for the development of a vaccine against malaria. PvTARAg55 polymorphisms were examined among isolates from various locations in Asian countries mainly; thus the current study could set the valuable baseline data for the development of a vaccine and clinical trials. A total of 59 samples were collected from Asian countries and one isolate from Africa. PvTARAg55 gene from 59 isolates was amplified, sequenced, and analyzed. PvTARAg55 contained a highly conserved tryptophan-rich domain (TRD) and a variable alanine-rich domain (ARD). In comparison to the Sal-1 strain, 10 allelic types of PvTARAg55 were found among 59 isolates. The main observed variations were the insertions and deletions of repeated sequences in the Ala-rich domain. Four types of GGVAAAP repeats were found at codon 324. Interestingly, GGVAAAP was found to be majority of Sal-1 type in the world. Two repeats (x2) were found in isolates from Korea, China, and India. Type of total deletion of GGVAAAP and three repeat (x3) were found from Indonesia isolates. Furthermore, “second insertion repeats” – with one or two repeats – were found with AFGAPSGFAPRP amino acid sequences at codon 338. Two repeats (x2) of AFGAPSGFAPRP were found in Indonesia, and PNG isolates. Finally, a “third repeat” was present with TTVNPEA amino acid sequences at codon 429 (the Indonesian isolates had three TTVNPEA sequences at that position). Isolates from ROK revealed “conserved sequences” in tryptophan-rich domain of PvTARAg55 with single amino acid substitutions (M180I). Hence, the extensive antigenic diversity of PvTARAg55 should be taken in account during the vaccine development.     

Genetic structure of Plasmodium vivax isolates from two malaria endemic areas in Afghanistan

In this study, the nature and extent of genetic diversity of Plasmodium vivax populations circulating in Afghanistan have been investigated by analyzing three genetic markers: csp, msp-1, and msp-3α. Blood samples (n = 202) were collected from patients presenting with vivax malaria from south-western (Herat) and south-eastern (Nangarhar) parts of Afghanistan, and analysed using nested-PCR/RFLP and sequencing methods. Genotyping pvmsp-1 revealed type 1, type 2 and recombinant type 3 allelic variants, with type 1 predominant in parasites in both study areas. The sequence analysis of 57 P. vivax isolates identified a total of 26 distinct alleles. Genotyping pvcsp gene showed that VK210 type (86.6%) is predominant in Afghanistan. Moreover, three major types of the pvmsp-3α locus: type A, type B and type C were distinguished among Afghani isolates. The predominant fragments among Nangarhar and Herat parasites were type A (70.8% and 67.9%, respectively). PCR/RFLP products with Hha I and Alu I were detected 52 and 38 distinct variants among Nangarhar and Herat isolates, respectively. These results strongly indicate that the P. vivax populations in Afghanistan are highly diverse.     

Plasmodium vivax in the Democratic Republic of East Timor: Parasite prevalence and antifolate resistance-associated mutations

In the Democratic Republic of East Timor, Plasmodium falciparum and Plasmodium vivax malaria coexist, but limited information is available about the latter species. Consequently, the prevalence of P. vivax and of its corresponding antifolate resistance-associated mutations in the pvdhfr and pvdhps genes was assessed here. Blood samples were collected from 650 individuals distributed among six districts, over two different periods, by either passive case detection (PCD) or active case detection (ACD). As expected, malaria was over-represented in the PCD sample (26% PCD vs 5% ACD), because the infection increases medical care seeking. Additionally, the relative frequency of P. vivax infections in symptomatic individuals (37%) was twice as high as the one in the asymptomatic sampling group (18%), suggesting that that this parasite is accounting for a significant proportion malaria-attributed morbidity. The frequency of specific sulfadoxine-pyrimethamine resistance-associated mutations genes was ascertained in P. vivax positive samples by PCR-RFLP. Although no mutants were detected in codons 383 and 553 of pvdhps, 48%, 76% and 82% of P. vivax-infected samples harbored the dhfr 33L, 58R and 117N mutations, respectively. Additionally, the frequency of parasites carrying both pvdhfr 58R and 117N mutant alleles accounted for a third of all genotypes analyzed, most likely due to inadvertent SP use in the past. In conclusion, evidence-based information is provided to promote optimized drug deployment and limit the evolution of resistance to antifolate resistance in P. vivax from East Timor.     

Detection of Plasmodium vivax infection in the Republic of Korea by loop-mediated isothermal amplification (LAMP)

Loop-mediated isothermal amplification (LAMP) is a novel technique that rapidly amplifies target DNA in isothermal conditions. In a previous study, the sensitivities and specificities of LAMP, microscopy, and nested PCR were compared in the context of rapid malaria detection. In the present study, LAMP detected vivax malaria parasites in 115 of 117 microscopically positive samples (sensitivity, 98.3%; 95% CI, 97.4-100%), which agreed well with the nested PCR results (sensitivity, 99.1%; 95% CI: 96.0-100%). No positive cases of malaria were detected by LAMP or nested PCR in 50 consecutive feverish patients other than malaria from malaria endemic areas. LAMP performed on DNA extracted from heat-treated blood had a sensitivity of 93.3% (28/30, 95% CI: 84.4-100%) and specificity of 100% (30/30, 95% CI: 100%). The present study shows that LAMP based assays have high sensitivity, specificity, and amplification efficiencies for Plasmodium vivax detection. The authors recommend that LAMP can be considered as a rapid nucleic acid amplification assay for the molecular diagnosis of P. vivax in both clinical laboratories and malaria clinics in areas where vivax malaria is endemic.     

In vivo experimental drug resistance study in Trypanosoma vivax isolates from tsetse infested and non-tsetse infested areas of Northwest Ethiopia

Ethiopia, particularly in the Northwest region, is affected by both tsetse fly and non-tsetse fly transmitted trypanosomosis with a significant impact on livestock productivity. The control of trypanosomosis in Ethiopia relies on either curative or prophylactic treatment of animals with diminazene aceturate (DA) or isometamidium chloride (ISM), respectively. However, since these two trypanocides have been on the market for more than 40 years, this may have resulted in drug-resistance. Therefore, in vivo drug resistance tests on two Ethiopian isolates of Trypanosoma vivax were completed, one from an area where tsetse flies are present and one from an area where tsetse flies are not present. Twenty four cattle (Bos indicus) aged between 6 and 12 months, purchased from a trypanosome-free area (Debre Brehan: Northcentral Ethiopia) and confirmed to be trypanosome-negative, were randomly assigned into four groups of six animals, which were infected with T. vivax isolated from a tsetse-infested or non-tsetse infested area, and in each case treated with curative doses of DA or ISM. Each animal were inoculated intravenously 3 × 10⁶ trypanosomes from donor animals. Parasitaemia became patent earlier in infections with non-tsetse T. vivax (∼7 days post-infection) than tsetse (∼14 days post-infection). Both groups were treated at the highest peak parasitaemia with DA or ISM and nine cattle, four with non-tsetse T. vivax (two ISM- and two DA-treated) and five with tsetse T. vivax (three ISM- and two DA-treated) showed relapses of parasitaemia. Moreover, treatment did not improve diagnostic host markers of trypanosome infections in these animals. In conclusion, in vivo drug tests indicated the presence of resistant parasites (>20% of treated animals in each group relapsed) against recommended doses of both available trypanocidal drugs.     

High frequency of genetic diversity of Plasmodium vivax field isolates in Myanmar

Malaria is one of the most serious problems threatening human health in Myanmar. Although the morbidity and mortality rates due to malaria have been gradually declining, Myanmar still contributes to a large proportion of malarial death in the South-East Asia region. However, little is known about the nature and extent of genetic diversity of the malarial parasites circulating in Myanmar. In this study, we investigated the overall infection status of Plasmodium and the population diversity of Plasmodium vivax by analyzing three genetic markers, circumsporozoite protein (CSP), merozoite surface protein-1 (MSP-1), and merozoite surface protein-3 (MSP-3α), of P. vivax field isolates collected from infected individuals. In 349 blood samples collected from the individuals who exhibited clinical symptoms associated with malaria, 63.0% showed a positive result for malaria (220/349). P. vivax was detected in 58.2% (128/220) and Plasmodium falciparum was detected in 29.1% (64/220). Mixed infections with both parasites were detected in 12.7% (28/220). The 116 blood samples in which single infection of P. vivax was confirmed were selected and subjected to further genetic analysis. Genotyping of the CSP gene of P. vivax showed that VK210 type (98.3%, 114/116) is predominant in Myanmar, but a significant level of mixed infections of VK210 and VK247 types (24.1%, 28/116) was also identified. Sequence analyses of MSP-1 and MSP-3α genes revealed a large number of distinguishable alleles: 12 for MSP-1 and 25 for MSP-3α. These results collectively suggest that the P. vivax population in Myanmar is highly diverse and multiple clonal infections are prevalent in the country.     

High prevalence of PfCRT K76T mutation in Plasmodium falciparum isolates in Ghana

Plasmodium falciparum has successfully developed resistance to almost all currently used antimalarials. A single nucleotide polymorphism in the P. falciparum chloroquine resistance transporter (Pfcrt) gene at position 76 resulting in a change in coding from lysine to threonine (K76T) has been implicated to be the corner stone of chloroquine resistance. Widespread resistance to chloroquine in endemic regions led to its replacement with other antimalarials. In some areas this replacement resulted in a reversion of the mutant T76 allele to the wild-type K76 allele. This study was conducted to determine the prevalence of the K76T mutation of the Pfcrt gene eight years after the ban on chloroquine sales and use. A cross-sectional study was conducted in 6 regional hospitals in Ghana. PCR-RFLP was used to analyse samples collected to determine the prevalence of Pfcrt K76T mutation. Of the 1318 participants recruited for this study, 246 were found to harbour the P. falciparum parasites, of which 60.98% (150/246) showed symptoms for malaria. The prevalence of the Pfcrt T76 mutant allele was 58.54% (144/246) and that of the K76 wild-type allele was 41.46% (102/246). No difference of statistical significance was observed in the distribution of the alleles in the symptomatic and asymptomatic participants (P = 0.632). No significant association was, again, observed between the alleles and parasite density (P = 0.314), as well as between the alleles and Hb levels of the participants (P = 0.254). Notwithstanding the decline in the prevalence of the Pfcrt T76 mutation since the antimalarial policy change in 2004, the 58.54% prevalence recorded in this study is considered high after eight years of the abolishment of chloroquine usage in Ghana. This is in contrast to findings from other endemic areas where the mutant allele significantly reduced in the population after a reduction chloroquine use.     

Mutant Plasmodium falciparum chloroquine resistance transporter in Hodeidah,Yemen: Association with parasitologic indices and treatment-seeking behaviors

Malaria still represents a major health problem in Yemen, particularly in Hodeidah, despite continuing efforts to eliminate it. With the absence of clinically proven vaccines, chemotherapy with antimalarials is still greatly needed. Chloroquine (CQ) has been popular as the drug of choice for malaria control. However, Plasmodium falciparum resistance to CQ has been one of the main obstacles in malaria control and elimination. Although CQ is no longer the recommended antimalarial chemotherapy, it has remained the number one over-the-counter antimalarial drug in many endemic areas, including Yemen, and is still used for self-medication. In addition, promising reports on CQ efficacy reversal in many African countries brought it again into the scene. This has led to a growing interest in the possibility of its re-introduction, particularly with the concerns raised about the parasite resistance to artemisinin-based combination therapies. Therefore, the present study aimed at analyzing the CQ-associated pfcrt 76T mutation in P. falciparum isolates from patients with uncomplicated falciparum malaria in Hodeidah, west of Yemen. The association of treatment-seeking behaviors and antimalarial drug use with the pfcrt 76T mutant allele was also studied. It was revealed that there is still a sustained high frequency of this molecular marker among parasite isolates associated with younger age, decreased parasite density and the presence of gametocytes in blood. Delay in seeking treatment and frequent use of antimalarials were the behaviors significantly associated with the presence of the pfcrt 76T mutant allele among patients reporting a history of malaria treatment.     

Clinical efficacy of chloroquine followed by primaquine for Plasmodium vivax treatment in Azerbaijan

Efficacy of chloroquine followed by primaquine has been monitored in 153 patients in seven districts of Azerbaijan. Chloroquine is fully effective over the first 14 days and the combination of chloroquine and primaquine is 100% effective over 28 days.     

An in vitro system for assessing the sensitivity of Plasmodium vivax to chloroquine

Following earlier observations on short-term culture of Plasmodium vivax, an in vitro test system has been developed for assessing the parasite's sensitivity to chloroquine. Fresh isolates with predominantly young trophozoites are diluted 1:19 with a (v/v=1/1) mixture of RPMI 1640 and Waymouth medium. The blood-medium mixture (BMM) is inoculated into the predosed microtitre plates before incubation in a candle jar. Incubation for 30 or 42 h yielded the best results. Incubation for 18 or 24 h was generally insufficient for an adequate development of the parasites. The reading of the test is based on stage-specific differential counts in the Giemsa-stained pre-incubation and post-incubation thick films, the evaluation on log-probit analysis of drug-related inhibition of parasite development. The test system has been evaluated on 200 fresh P. vivax isolates in an area with satisfactory clinical-parasitological response to chloroquine. At 30 or 42 h incubation 121 isolates (61.5%) showed adequate control growth and yielded valid sensitivity tests. Complete inhibition of parasite development occurred within the concentration range of 40-1280 nM. The mean EC50 for 30 h of incubation was 50.3 nM, as compared to 49.7 nM with 42 h of incubation. The geometric mean cut-off concentration of parasite development was 488 nM with 30 h of incubation as against 470 nM with 42 h of incubation.     

Association between chloroquine resistance phenotypes and point mutations in pfcrt and pfmdr1 in Plasmodium falciparum isolates from Thailand

The relationship between the in vitro susceptibility of Plasmodium falciparum isolates to the quinoline antimalarials chloroquine (CQ), mefloquine (MQ), and quinine (QN), and pfcrt and pfmdr1 gene polymorphisms were investigated. Field isolates (110 samples) were collected from various endemic areas of Thailand throughout 2002-2004. The pfcrt 76T allele was identified in 109 isolates (99.1%) while pfcrt 76K was found in a single (0.9%) isolate. The pfmdr 86N, 86Y, and the combination (86N + 86Y) alleles were identified in 83 (75.5%), 22 (20%), and 5 (4.5%) isolates, respectively. The pfmdr1 1042N, 1042D alleles and a mixture (1042N + 1042D) of the alleles were found in 94 (85.5%), 12 (10.9%) and 4 (3.6%) isolates, respectively. The pfmdr1 1246Y allele was detected in a single (0.9%) isolate. The pfmdr1 gene polymorphisms (86-1042-1246) was grouped into seven haplotypes as follows: N-N-D (68 isolates; 61.2%), Y-N-D (22 isolates; 19.8%), N-D-D (11 isolates; 9.9%), N-D-Y (1 isolate; 0.9%), N/Y-N-D (4 isolates; 3.6%), N-N/D-D (3 isolates; 2.7%), and N/Y-N/D-D (1 isolate; 0.9%). Eight different combinations of pfcrt-pfmdr1 genotypes were observed. Only one CQ-, MQ- and QN-sensitive isolate was found at the Thai-Laos border and no cases of QN resistance were found in this study.     

Non-allele specific antibody responses to genetically distinct variant forms of Plasmodium vivax Duffy binding protein (PvDBP-II) in Iranians exposed to seasonal malaria transmission

Duffy binding protein (DBP) is a leading vaccine candidate of Plasmodium vivax. The binding domain of DBP (DBP-II) is polymorphic, that may be a major challenge for development of a broadly effective vaccine against vivax malaria. The present investigation was undertaken to explore whether the sequence diversity of DBP-II causes variation in naturally acquired anti-DBP-II antibodies. In this study, the five genetically distinct variants were expressed, and anti-DBP-II responses were measured in P. vivax-infected individuals (n = 202). Finally, by performing immune-depletion ELISA experiments, antibody responses to the conserved sites of all allelic forms were evaluated using the corresponding and non-corresponding patients’ sera (n = 20). In this study, natural P. vivax infection produces IgG against all five examined variant forms of PvDBP-II with no statistically difference. Sequence analysis in the 20 selected samples (for antibody depletion experiment) showed eight distinct haplotypes, DBPI (n = 1), DBPIII (n = 3), DBPIV (n = 1), DBPV (n = 1), DBPVI (n = 5), DBPIX (n = 6), DBPX (n = 1), and DBP XI (n = 2). The results showed the presence of the cross-reactive antibody responses to heterologous variants of PvDBP-II in Iranian individuals who were infected with distinct allelic forms of the PvDBP-II. Therefore, it is proposed that the majority of antibodies recognized sharing B-cell epitopes and this could overcome the PvDBP-II variation as a one of the biggest challenges of PvDBP-II-based vaccine development.     

IgG subclasses pattern and high-avidity antibody to the C-terminal region of merozoite surface protein 1 of Plasmodium vivax in an unstable hypoendemic region in Iran

The C-terminal region of Plasmodium vivax merozoite surface protein 1 (PvMSP-1₁₉) is a leading vaccine candidate for inclusion in a polyvalent malaria vaccine. In the present study, the IgG subclasses profile and the avidity of IgG to PvMSP-1₁₉ were evaluated in individuals (n = 94) naturally exposed to P. vivax parasite in malaria endemic areas in Chabahar districts, Iran. In individuals with patent P. vivax malaria, 86.1% was sero-positive to PvMSP-1₁₉ and IgG1 (81.9%) was the predominant subclass. In addition, to determine the persistence of specific IgG, IgG1 and IgG3 antibodies to PvMSP-1₁₉, the frequency of antibodies was determined in the infected subjects (n = 74) after treatment with standard chloroquine and it was detected that the frequency of responders was significantly reduced to 51.3%, 51% and 16.2%, respectively. The antigen-binding avidity of IgG antibodies to PvMSP-1₁₉ was measured in sero-positive sera and the high-avidity of IgG, IgG1 and IgG3 was found in 66.6%, 61% and 47% of the infected subjects with P. vivax, respectively. The present result shows that individuals who exposed to vivax malaria in the endemic region in Iran develop antibodies with high-avidity to PvMSP-1₁₉. These results could help to understand the interactions between the host and P. vivax parasite in development of MSP-1₁₉-based vaccine.     

Genetic diversity of transmission blocking vaccine candidate (Pvs25 and Pvs28) antigen in Plasmodium vivax clinical isolates from Iran

The leading candidates for a Transmission Blocking Vaccine (TBV) in Plasmodium vivax parasite are the ookinete surface protein 25 (Pvs25) and Pvs28, which their phase I clinical trial is ongoing. Therefore, we carried out survey of polymorphisms of the pvs25 and pvs28 genes in P. vivax populations that are circulating in the two malaria areas of contrasting endemicity in Iran, before field application of the TBV. To characterize the polymorphisms of pvs25 and pvs28 genes, 50 isolates were analyzed by sequencing method and their gene structure was compared with parasite populations from India, Bangladesh, Indonesia, Thailand, Mexico and Brazil. Three mutations were detected in pvs25 and pvs28 including Q87K, E97Q, I130T and M52L, T65K, T140S with two and four distinct haplotypes, in comparison with the Sal I sequence type, respectively. Both haplotypes of Pvs25 were found among northern and southern P. vivax isolates; however, only two and three of the Pvs28 variants were observed among the northern and southern isolates, respectively. In conclusion, the present results show the limited sequence polymorphism of the pvs25 and pvs28 genes among field P. vivax population in Iran. These results highly encourage with respect to applicability of Pvs25 and Pvs28-based vaccine against P. vivax infection in the region, where these parasites are prevalent, whether these occur in the temperate or tropical zones.     

The periodicity of Plasmodium vivax and Plasmodium falciparum in Venezuela

We investigated the periodicity of Plasmodium vivax and P. falciparum incidence in time-series of malaria data (1990–2010) from three endemic regions in Venezuela. In particular, we determined whether disease epidemics were related to local climate variability and regional climate anomalies such as the El Niño Southern Oscillation (ENSO). Malaria periodicity was found to exhibit unique features in each studied region. Significant multi-annual cycles of 2- to about 6-year periods were identified. The inter-annual variability of malaria cases was coherent with that of SSTs (ENSO), mainly at temporal scales within the 3–6 year periods. Additionally, malaria cases were intensified approximately 1 year after an El Niño event, a pattern that highlights the role of climate inter-annual variability in the epidemic patterns. Rainfall mediated the effect of ENSO on malaria locally. Particularly, rains from the last phase of the season had a critical role in the temporal dynamics of Plasmodium. The malaria–climate relationship was complex and transient, varying in strength with the region and species. By identifying temporal cycles of malaria we have made a first step in predicting high-risk years in Venezuela. Our findings emphasize the importance of analyzing high-resolution spatial–temporal data to better understand malaria transmission dynamics.