Plasmodium vivax in India

Four Plasmodium species cause malaria in humans: Plasmodium vivax is the most widespread and results in pronounced morbidity. India (population >1 billion) is a major contributor to the burden of vivax malaria. With a resurgence in interest concerning the neglected burden of vivax malaria and the completion of the P. vivax genome, it is timely to review what is known concerning P. vivax in India. The P. vivax population is highly diverse in terms of relapse patterns, drug response and clinical profiles, and highly genetically variable according to studies of antigen genes, isoenzyme markers and microsatellites. The unique epidemiology of malaria in India, where P. vivax predominates over Plasmodium falciparum, renders this location ideal for studying the dynamics of co-infection.     

Characterizing the spatial and temporal variation of malaria incidence in Bangladesh, 2007

ABSTRACT: BACKGROUND: Malaria remains a significant health problem in Bangladesh affecting 13 of 64 districts. The risk of malaria is variable across the endemic areas and throughout the year. A better understanding of the spatial and temporal patterns in malaria risk and the determinants driving the variation are crucial for the appropriate targeting of interventions under the National Malaria Control and Prevention Programme. METHODS: Numbers of Plasmodium falciparum and Plasmodium vivax malaria cases reported by month in 2007, across the 70 endemic thanas (sub-districts) in Bangladesh, were assembled from health centre surveillance reports. Bayesian Poisson regression models of incidence were constructed, with fixed effects for monthly rainfall, maximum temperature and elevation, and random effects for thanas, with a conditional autoregressive prior spatial structure. RESULTS: The annual incidence of reported cases was 34.0 and 9.6 cases/10,000 population for P. falciparum and P. vivax respectively and the population of the 70 malaria-endemic thanas was approximately 13.5 million in 2007. Incidence of reported cases for both types of malaria was highest in the mountainous south-east of the country (the Chittagong Hill Tracts). Models revealed statistically significant positive associations between the incidence of reported P. vivax and P. falciparum cases and rainfall and maximum temperature. CONCLUSIONS: The risk of P. falciparum and P. vivax was spatially variable across the endemic thanas of Bangladesh and also highly seasonal, suggesting that interventions should be targeted and timed according to the risk profile of the endemic areas. Rainfall, temperature and elevation are major factors driving the spatiotemporal patterns of malaria in Bangladesh.     

Dipsticks for rapid detection of Plasmodium in vectoring Anopheles mosquitoes

Malaria remains the most serious vector-borne disease, affecting some 300-500 million people annually, transmitted by many species of Anopheles mosquitoes (Diptera: Culicidae). Monoclonal antibodies developed against specific circumsporozoite (CS) proteins of the main malaria parasites Plasmodium falciparum and P. vivax have been used previously for enzyme-linked immunosorbent assays (ELISA), widely employed for detection of malaria sporozoites in vector Anopheles for local risk assessment, epidemiological studies and targeting vector control. However, ELISA procedures are relatively slow and impractical for field use. To circumvent this, we developed rapid wicking assays that identify the presence or absence of specific peptide epitopes of CS protein of the most important P. falciparum and two strains (variants 210 and 247) of the more widespread P. vivax. The resulting assay is a rapid, one-step procedure using a 'dipstick' wicking test strip. In laboratory assessment, dipsticks identified 1 ng/ mL of any of these three CS protein antigens, with sensitivity nearly equal to the CS standard ELISA. We have developed and are evaluating a combined panel assay that will be both qualitative and quantitative. This quick and easy dipstick test (VecTest Malaria) offers practical advantages for field workers needing to make rapid surveys of malaria vectors.     

Performance of OptiMAL(R) in the diagnosis of Plasmodium vivax and Plasmodium falciparum infections in a malaria referral center in Colombia

Alternative, non-microscopic methods for the diagnosis of malaria have recently become available. Among these, rapid dipstick methods stand out. One such test, OptiMAL(R), is based on the immunochromatographic detection of Plasmodium lactate dehydrogenase (pLDH) and has the capacity to detect and distinguish infections caused by P. falciparum and Plasmodium sp. This capacity is particularly important in countries where different species of Plasmodium co-exist. In this study we evaluated the performance of OptiMAL(R) in an urban referral center for malaria diagnosis. Two sets of patients were included: one (n = 112) having predetermined infections with P. falciparum or P. vivax and individuals with negative blood smears; and another consisting of all eligible consecutive patients (n = 80) consulting for diagnosis at the referral center during one month. The overall diagnostic efficiency of OptiMAL(R) for both sets of patients was 96.9%. Efficiency was higher for P. vivax (98.1%) than for P. falciparum (94.9%). These results corroborate the diagnostic utility of OptiMAL(R) in settings where P. vivax and P. falciparum co-exist and support its implementation where microscopic diagnosis is unavailable and in circumstances that exceed the capacity of the local microscopic diagnosis facility.     

Human T-cell responses to malaria: mostly forgotten or committed to memory?

T cells have been implicated in both malaria immunity and malaria disease and factors controlling the maintenance of T-cell responses over time may alter the clinical outcome o f infection. Michael Good and Janine Bilsborough have compared the T-cell responses to epitopes from the Plasmodium vivax and P. falciparum circumsporozoite proteins and here discuss the issue of T-cell memory as it applies to malaria.     

Malaria seroepidemiology: comparison between indirect fluorescent antibody test and enzyme immunoassay using bloodspot eluates.

Blood sampling on filter paper is a current practice in malaria seroepidemiological studies by indirect fluorescent antibody test (IFAT). There is, however, scant comparative information about the use of bloodspot eluates for detection of malarial IgG antibodies simultaneously by IFAT and enzyme immunoassay (ELISA). Here we report data obtained by both serological methods done on 219 bloodspot eluate samples collected in a rural community in Brazilian Amazon Basin (Alto Paraíso, Ariquemes municipality) where malaria is endemic. Plasmodium falciparum and P. vivax thick smear antigens were used in the IFAT; a detergent-soluble P. falciparum antigen was prepared for ELISA. Substantial agreement of results (Kappa coefficient k = 0.686) was observed when P. falciparum antigen was used in both tests, and IFAT titers were found to be strongly correlated to ELISA antibody units (Spearman correlation coefficient rs = 0.818, p < 0.001). Only moderate agreement (k = 0.467) between IFAT with P. vivax antigen and ELISA with P. falciparum antigen was observed. Spearman correlation coefficient value between quantitative results (IFAT titers and ELISA antibody units) in this case was numerically lower (rs = 0.540, p < 0.0001). Our results suggest that, with P. falciparum antigen, both IFAT and ELISA performed on bloodspot eluates are equivalent for seroepidemiological purposes.     

Comparative evolutionary genomics of human malaria parasites

The parasites Plasmodium falciparum and Plasmodium vivax are responsible for the majority of human malaria cases worldwide. Despite many similarities in their biology, they frequently are studied in isolation. With the completion of the P. vivax genome and the generation of an initial P. falciparum genetic diversity map, attempts are being made to infer inter- and intra-species genome evolution. Here, we briefly review our current knowledge of comparative evolutionary genomics of the two species in the light of several presentations at the Molecular Approaches to Malaria 2008 meeting in Lorne, Australia and ask the question: can evolutionary genomics of one species inform the other?     

Possible role of Granulocyte Macrophage Colony Stimulating Factor receptor (GM-CSF R) in malaria

Malaria has been reportedly increasing in incidence on the globe. Evidence from clinical studies supports a role for cytokines in the pathogenesis of cerebral malaria. Given the stimulatory effect of the ligand GM-CSF on the synthesis and release of the pyrogenic cytokine TNF alpha, the present study has been undertaken to investigate a possible role of GMCSF receptor in the pathogenesis of both Plasmodium vivax and Plasmodium falciparum malaria. An enzyme immunoassay developed by us at our laboratory for the quantitation of GM-CSF receptor has been used. No changes in the concentration of the receptor have been indicated either at the time of diagnosis or after treatment. In addition, an intercomparison of the receptor concentration between the P. vivax and P. falciparum groups does not show any significant difference. The results suggest that GM-CSF receptor has no significant role in the pathogenesis of either type of malaria.     

Prevalence and level of antibodies to the circumsporozoite protein of human malaria parasites in five states of the Amazon region of Brazil

The aim of this study was to determine the prevalence of malaria infection and antibodies against the repetitive epitopes of the circumsporozoite (CS) proteins of Plasmodium falciparum, P. malariae, P. vivax VK210, P. vivax VK247, and P. vivax-like in individuals living in the states of Rond?nia, Pará, Mato Grosso, Amazonas, and Acre. Active malaria transmission was occurring in all studied sites, except in Acre. P. falciparum was the predominant species in Pará and Rond?nia and P. vivax in Mato Grosso. Infection by P. malariae was low but this Plasmodium species was detected in Rond?nia (3.5%), Mato Grosso (2.5%), and Pará (0.8%). High prevalence and levels of serological reactivity against the CS repeat peptides of P. falciparum were detected in Rond?nia (93%) and Pará (85%). Sera containing antibodies against the CS repeat of P. malariae occurred more frequently in Rond?nia (79%), Pará (76%), and Amazonas (68%). Antibodies against the repeat epitope of the standard CS protein of P. vivax VK210, P. vivax VK247, and P. vivax-like were more frequent in Rond?nia, Pará, and Mato Grosso. The high frequency of reactions to P. malariae in most of the areas suggests that the infection by this Plasmodium species has been underestimated in Brazil.     

Widespread occurrence of antibodies against circumsporozoite protein and against blood forms of Plasmodium vivax, P. falciparum and P. malariae in Brazilian wild monkeys

BACKGROUND: A survey of malaria antibodies was carried out over 7 years and a total of 777 serum samples from wild monkeys were collected in three distinct ecological areas of Brazil where autochthonous malaria has been reported: the 'Cerrado' (similar to savanna), the Atlantic Forest and the Atlantic Semideciduous Forest. METHODS: We carried out enzyme-linked immunosorbent assay to investigate the presence of IgG antibodies against peptides of the circumsporozoite protein (CSP) repeat region of 'classic'Plasmodium vivax, P. vivax VK247, human P. vivax-like/P. simiovale, P. brasilianum/P. malariae and P. falciparum. We also carried out immunofluorescence assay with asexual forms of P. vivax, P. malariae and P. falciparum. RESULTS: The high prevalence of antibodies against CSP in all areas indicates that the monkeys had intense contact with sporozoites from infected anophelines. The immune response against asexual forms of Plasmodium in the monkeys from the Atlantic Forest indicates the development of the infection. CONCLUSIONS: We discuss the possibility of monkeys being malaria reservoirs in non-endemic areas.     

Mass blood survey for malaria: pooling and realtime PCR combined with expert microscopy in north-west Thailand

ABSTRACT: BACKGROUND: Asymptomatic carriage of Plasmodium falciparum and Plasmodium vivax is common in both low-and high-transmission settings and represents an important reservoir of infection that needs to be targeted if malaria elimination is to succeed. METHODS: Mass blood examinations (475 individuals) were conducted in two villages in Mae Hong Son, an area of endemic but low-transmission malaria in the north-west of Thailand. The microscopist at the local malaria clinic did not detect any infections. Pools of four samples were screened by real-time PCR; individual members of all of the positive pools were then re-examined by expert microscopy and by a second species-specific PCR reaction. RESULTS: Eight subjects were found to be positive by both PCR and expert microscopy and one was found to be positive by PCR alone. The slides contained asexual stage parasites of P. vivax, P. falciparum and Plasmodium malariae, but no gametocytes. The local clinic was notified within two to eight days of the survey. CONCLUSION: A combination of pooling, real-time PCR and expert microscopy provides a feasible approach to identifying and treating asymptomatic malaria infections in a timely manner.     

Serological detection of Plasmodium vivax malaria using recombinant proteins corresponding to the 19-kDa C-terminal region of the merozoite surface protein-1

BACKGROUND: Serological tests to detect antibodies specific to Plasmodium vivax could be a valuable tool for epidemiological studies, for screening blood donors in areas where the malaria is not endemic and for diagnosis of infected individuals. Because P. vivax cannot be easily obtained in vitro, ELISA assays using total or semi-purified antigens are rarely used. Based on this limitation, we tested whether recombinant proteins representing the 19 kDa C-terminal region of the merozoite surface protein-1 of P. vivax (MSP119) could be useful for serological detection of malaria infection. METHODS: Three purified recombinant proteins produced in Escherichia coli (GST-MSP119, His6-MSP119 and His6-MSP119-PADRE) and one in Pichia pastoris (yMSP119-PADRE) were compared for their ability to bind to IgG antibodies of individuals with patent P. vivax infection. The method was tested with 200 serum samples collected from individuals living in the north of Brazil in areas endemic for malaria, 53 serum samples from individuals exposed to Plasmodium falciparum infection and 177 serum samples from individuals never exposed to malaria. RESULTS: Overall, the sensitivity of the ELISA assessed with sera from naturally infected individuals was 95%. The proportion of serum samples that reacted with recombinant proteins GST-MSP119, His6-MSP119, His6-MSP119-PADRE and yMSP119-PADRE was 90%, 93.5%, 93.5% and 93.5%, respectively. The specificity values of the ELISA determined with sera from healthy individuals and from individuals with other infectious diseases were 98.3% (GST-MSP119), 97.7% (His6-MSP119 and His6-MSP119-PADRE) or 100% (yMSP119-PADRE). CONCLUSIONS: Our study demonstrated that for the Brazilian population, an ELISA using a recombinant protein of the MSP119 can be used as the basis for the development of a valuable serological assay for the detection of P. vivax malaria.     

New serological test for malaria antibodies.

In an enzyme-linked immunosorbent assay test for malaria antibodies, antibodies to Plasmodium vivax and P. falciparum in man are detected using a crude antigen prepared from the simian malaria parasite P. knowlesi. The test may be suitable for epidemiological studies.     

Current scenario of malaria in India

The Indian National Malaria Eradication Programme (NMEP) is reporting 2.5 to 3 million malaria cases, and about 1,000 malaria deaths annually. Malaria in the northeastern states is stable and in the peninsular India unstable. There are six major and three minor malaria vectors, of which Anopheles culicifacies transmits malaria in rural areas and An. stephensi in the towns. Other vectors are of local importance. Plasmodium vivax is the dominant infection and accounts for 60-65% cases whereas P. falciparum contributes 30-35% cases. Field operations to control malaria are impeded by resistance and/or exophilic vector behavior, parasite resistance to antimalarial drugs, operational problems in spraying, failure to search breeding of mosquitoes at weekly intervals, staff shortages and financial constraints. Resurgent malaria invaded new ecotypes created by green revolution, industrial growth and urban development resulting in paradigm shift towards man-made malaria. NMEP has launched a world bank-assisted enhanced malaria control project with primary emphasis to protect 62.2 million high risk population in 7 states.     

Radical curative efficacy of five-day regimen of primaquine for treatment of Plasmodium vivax malaria in India

For over 4 decades the antimalarial program in India has been prescribing a 5-day primaquine regimen as an antirelapse therapy to treat Plasmodium vivax malaria. In view of conflicting reports on the effectiveness of this regimen in the Indian subcontinent, and the varying prevalence of P. vivax in various ecosystems in India, the antirelapse efficacy of this regimen was evaluated in Orissa, a malaria endemic state in eastern India where P. falciparum predominates. In 723 cases of P. vivax infection treated with chloroquine alone and followed up weekly for 1 yr, the prevalence of recurrence of parasitaemia with fever was 8.6%. Among another 759 P. vivax cases treated with chloroquine and a 5-day regimen of primaquine at 15 mg/day (adult dose), the recurrence of infection was 6.5%. The difference in recurrence was not significant (P = 0.53). It is important to note that in a great majority of cases of P. vivax in this area, infection did not recur even without treatment with primaquine. This finding, that the use of the 5-day primaquine regimen with chloroquine had no significant advantage over the use of chloroquine alone, undermines the rationale of using primaquine as an antirelapse drug in forested areas with a high prevalence of P. falciparum.     

Contemporaneous and successive mixed Plasmodium falciparum and Plasmodium vivax infections are associated with Ascaris lumbricoides: an immunomodulating effect?

Following an investigation suggesting a protective role for Ascaris against cerebral malaria, possibly through immunomodulation, we examined whether Ascaris had any impact on mixed Plasmodium falciparum and Plasmodium vivax infections. We studied a cross section of 928 patient files between 1991 and 1999. Forty patients had contemporaneous mixed infections and 40 patients had P. falciparum infections, followed by P. vivax infections. There was a significant association between Ascaris infection and risk of having both contemporaneous or successive mixed P. falciparum and P. vivax infections (adjusted odds ratios respectively 6 [2-18] P = 0.001 and 3.6 [1.2-11.1] P = 0.02). There was a positive linear trend between the burden of Ascaris and the risk of mixed infections P < 0.0001. These results suggested the possibility that pre-existing Ascaris infection may increase tolerance of the host to different Plasmodium spp., thus facilitating their coexistence.     

Serological investigations in retrospective diagnosis of malaria.

Sera were obtained in 415 known cases of malaria (88 residents, 327 immigrants) at different times after diagnosis. Three antigens were used in the indirect fluorscence antibody test to detect antibodies to either Plasmodium falciparum or P vivax. Results in residents and immigrants were analysed separately. Most residents had detectable antibodies within one week after an attack, which began to wane after a month. The strongest reactions were obtained in cases of falciparum malaria with the homologous antigen and in cases of vivax malaria with P fieldi. The overall pattern of results was the same in the immigrants but the proportions positive for malaria antibodies, mean titres, persistence of antibodies, and the cross-reaction were usually greater. Testing for malaria antibodies is probably of value in the retrospective differential diagnosis of malaria in patients who have not been exposed to malaria before but must be interpreted with caution in others.     

Severe disease in children hospitalized with a diagnosis of Plasmodium vivax in south-eastern Pakistan

ABSTRACT: BACKGROUND: Infection by Plasmodium vivax has been considered rarely threatening to life, but recent studies challenge this notion. This study documented the frequency and character of severe illness in paediatric patients admitted to a hospital in south-eastern Pakistan with a laboratory-confirmed diagnosis of vivax malaria. METHODS: An observational study of all 180 paediatric patients admitted with any diagnosis of malaria during 2010 was conducted: 128 P. vivax; 48 Plasmodium falciparum; and four mixed infections of these species. Patients were classified as having severe illness with any of the following indicators: Glascow coma scale <11; >2 convulsions; haemoglobin <5g/dL; thrombocytes <50,000/mL; blood glucose <45mg%; >70 breaths/min; or intravenous antimalarial therapy. Additionally, 64 patients with a diagnosis of vivax malaria were treated during 2009, and the 21 of these having severe illness were included in analyses of the frequency and character of severe illness with that diagnosis. RESULTS: During 2010, 39 (31%) or 37 (77%) patients with a diagnosis of P. vivax or P. falciparum were classified as having severe disease. Including the 2009 records of 64 patients having vivax malaria, a total of 60 (31%) patients with severe illness and a diagnosis of P. vivax were available. Altered mental status (Glascow coma scale score <11; or >2 convulsions) dominated at 54% of the 83 indicators of severe illness manifest among the patients with vivax malaria, as was true among the 37 children with a diagnosis of falciparum malaria and being severely ill; 58% of the 72 indicators of severe disease documented among them. No statistically significant difference appeared in frequencies of any other severe disease indicators between patients diagnosed with vivax or falciparum malaria. Despite such similarities, a diagnosis of falciparum malaria nonetheless came with 3.8-fold (95% CI = 1.8- 8.1) higher risk of presenting with severe illness, and 8.0-fold (95% CI = 2.1-31) greater likelihood of presenting with three or more severe disease indicators. Two patients did not survive hospitalization, one each with a diagnosis of falciparum or vivax malaria. CONCLUSIONS: Vivax malaria caused a substantial burden of potentially life-threatening morbidity on a paediatric ward in a hospital in south-eastern Pakistan.