An overview of malaria transmission from the perspective of Amazon Anopheles vectors

In the Americas, areas with a high risk of malaria transmission are mainly located in the Amazon Forest, which extends across nine countries. One keystone step to understanding the Plasmodium life cycle in Anopheles species from the Amazon Region is to obtain experimentally infected mosquito vectors. Several attempts to colonise Ano- pheles species have been conducted, but with only short-lived success or no success at all. In this review, we review the literature on malaria transmission from the perspective of its Amazon vectors. Currently, it is possible to develop experimental Plasmodium vivax infection of the colonised and field-captured vectors in laboratories located close to Amazonian endemic areas. We are also reviewing studies related to the immune response to P. vivax infection of Anopheles aquasalis, a coastal mosquito species. Finally, we discuss the importance of the modulation of Plasmodium infection by the vector microbiota and also consider the anopheline genomes. The establishment of experimental mosquito infections with Plasmodium falciparum, Plasmodium yoelii and Plasmodium berghei parasites that could provide interesting models for studying malaria in the Amazonian scenario is important. Understanding the molecular mechanisms involved in the development of the parasites in New World vectors is crucial in order to better determine the interaction process and vectorial competence.

A historical perspective on malaria control in Brazil

Malaria has always been an important public health problem in Brazil. The early history of Brazilian malaria and its control was powered by colonisation by Europeans and the forced relocation of Africans as slaves. Internal migration brought malaria to many regions in Brazil where, given suitableAnopheles mosquito vectors, it thrived. Almost from the start, officials recognised the problem malaria presented to economic development, but early control efforts were hampered by still developing public health control and ignorance of the underlying biology and ecology of malaria. Multiple regional and national malaria control efforts have been attempted with varying success. At present, the Amazon Basin accounts for 99% of Brazil’s reported malaria cases with regional increases in incidence often associated with large scale public works or migration. Here, we provide an exhaustive summary of primary literature in English, Spanish and Portuguese regarding Brazilian malaria control. Our goal was not to interpret the history of Brazilian malaria control from a particular political or theoretical perspective, but rather to provide a straightforward, chronological narrative of the events that have transpired in Brazil over the past 200 years and identify common themes.

Aspidosperma (Apocynaceae) plant cytotoxicity and activity towards malaria parasites. Part II: experimental studies withAspidosperma ramiflorum in vivo and in vitro

Several species of Aspidosperma plants are used to treat diseases in the tropics, including Aspidosperma ramiflorum, which acts against leishmaniasis, an activity that is experimentally confirmed. The species, known as guatambu-yellow, yellowperoba, coffee-peroba andmatiambu, grows in the Atlantic Forest of Brazil in the South to the Southeast regions. Through a guided biofractionation of A. ramiflorum extracts, the plant activity against Plasmodium falciparum was evaluated in vitro for toxicity towards human hepatoma G2 cells, normal monkey kidney cells and nonimmortalised human monocytes isolated from peripheral blood. Six of the seven extracts tested were active at low doses (half-maximal drug inhibitory concentration < 3.8 µg/mL); the aqueous extract was inactive. Overall, the plant extracts and the purified compounds displayed low toxicity in vitro. A nonsoluble extract fraction and one purified alkaloid isositsirikine (compound 5) displayed high selectivity indexes (SI) (= 56 and 113, respectively), whereas compounds 2 and 3 were toxic (SI < 10). The structure, activity and low toxicity of isositsirikine in vitro are described here for the first time in A. ramiflorum, but only the neutral and precipitate plant fractions were tested for activity, which caused up to 53% parasitaemia inhibition of Plasmodium bergheiin mice with blood-induced malaria. This plant species is likely to be useful in the further development of an antimalarial drug, but its pharmacological evaluation is still required.

Immunoregulation in human malaria: the challenge of understanding asymptomatic infection

Asymptomatic Plasmodium infection carriers represent a major threat to malaria control worldwide as they are silent natural reservoirs and do not seek medical care. There are no standard criteria for asymptomaticPlasmodium infection; therefore, its diagnosis relies on the presence of the parasite during a specific period of symptomless infection. The antiparasitic immune response can result in reducedPlasmodium sp. load with control of disease manifestations, which leads to asymptomatic infection. Both the innate and adaptive immune responses seem to play major roles in asymptomatic Plasmodiuminfection; T regulatory cell activity (through the production of interleukin-10 and transforming growth factor-β) and B-cells (with a broad antibody response) both play prominent roles. Furthermore, molecules involved in the haem detoxification pathway (such as haptoglobin and haeme oxygenase-1) and iron metabolism (ferritin and activated c-Jun N-terminal kinase) have emerged in recent years as potential biomarkers and thus are helping to unravel the immune response underlying asymptomatic Plasmodium infection. The acquisition of large data sets and the use of robust statistical tools, including network analysis, associated with well-designed malaria studies will likely help elucidate the immune mechanisms responsible for asymptomatic infection.

Malaria in gold-mining areas in Colombia

Gold-mining may play an important role in the maintenance of malaria worldwide. Gold-mining, mostly illegal, has significantly expanded in Colombia during the last decade in areas with limited health care and disease prevention. We report a descriptive study that was carried out to determine the malaria prevalence in gold-mining areas of Colombia, using data from the public health surveillance system (National Health Institute) during the period 2010-2013. Gold-mining was more prevalent in the departments of Antioquia, Córdoba, Bolívar, Chocó, Nariño, Cauca, and Valle, which contributed 89.3% (270,753 cases) of the national malaria incidence from 2010-2013 and 31.6% of malaria cases were from mining areas. Mining regions, such as El Bagre, Zaragoza, and Segovia, in Antioquia, Puerto Libertador and Montelíbano, in Córdoba, and Buenaventura, in Valle del Cauca, were the most endemic areas. The annual parasite index (API) correlated with gold production (R2 0.82, p < 0.0001); for every 100 kg of gold produced, the API increased by 0.54 cases per 1,000 inhabitants. Lack of malaria control activities, together with high migration and proliferation of mosquito breeding sites, contribute to malaria in gold-mining regions. Specific control activities must be introduced to control this significant source of malaria in Colombia.

Malaria vaccine: roadblocks and possible solutions

Malaria remains the most prevalent and devastating parasitic disease worldwide. Vaccination is considered to be an approach that will complement other strategies for prevention and control of the disease in the future. In the last 10 years, intense studies aimed at the development of a malaria vaccine have provided important knowledge of the nature of the host immunological mechanisms of protection and their respective target antigens. It became well established that protective immune responses can be generated against the distinct stages of Plasmodium. However, in general, protective immune responses are directed at stage-specific antigens. The elucidation of the primary structure of these antigens made possible the generation of synthetic and recombinant proteins that are being extensively used in experimental immunizations against the infection. Today, several epitopes of limited polymorphism have been described and protective immunity can be generated by immunization with them. These epitopes are being tested as primary candidates for a subunit vaccine against malaria. Here we critically review the major roadblocks for the development of a malaria vaccine and provide some insight on how these problems are being solved

Mapping cancer, cardiovascular and malaria research in Brazil

This paper presents performance indicators for the Brazilian cancer, cardiovascular and malaria research areas from 1981 to 1995. The data show an increasing number of papers since 1981 and author numbers indicate a continuous growth of the scientific community and suggest an expected impact of scientific activity on biomedical education. The data also characterize cardiovascular research as a well-established area and cancer research as a faster growing consolidating field. The 1989-1994 share of Brazilian articles among world publications shows a growing trend for the cancer (1.61) and cardiovascular (1.59) areas, and a decrease for the malaria area (0.89). The burden of the three diseases on society is contrasted by the small number of consolidated Brazilian research groups, and a questionable balance of thematic activity, especially with regard to malaria. Brazilian periodicals play an important role in increasing the international visibility of science produced in the country. Cancer and cardiovascular research is strongly concentrated in the Southeastern and in Southern regions of Brazil, especially in São Paulo (at least one address from São Paulo in 64.5% of the 962 cancer articles and in 66.9% of the 2250 cardiovascular articles, the second state being Rio de Janeiro with at least one address in 14.1 and 11% of those articles, respectively). Malaria research (468 articles) is more evenly distributed across the country, following the pattern of the endemic distribution of the disease. Surveying these national indicator trends can be useful to establish policies in the decision process about health sciences, medical education and public health.

Melatonin and N-acetyl-serotonin cross the red blood cell membrane and evoke calcium mobilization in malarial parasites

The duration of the intraerythrocytic cycle of Plasmodium is a key factor in the pathogenicity of this parasite. The simultaneous attack of the host red blood cells by the parasites depends on the synchronicity of their development. Unraveling the signals at the basis of this synchronicity represents a challenging biological question and may be very important to develop alternative strategies for therapeutic approaches. Recently, we reported that the synchrony of Plasmodium is modulated by melatonin, a host hormone that is synthesized only during the dark phases. Here we report that N-acetyl-serotonin, a melatonin precursor, also releases Ca2+ from isolated P. chabaudi parasites at micro- and nanomolar concentrations and that the release is blocked by 250 mM luzindole, an antagonist of melatonin receptors, and 20 mM U73122, a phospholipase C inhibitor. On the basis of confocal microscopy, we also report the ability of 0.1 µM melatonin and 0.1 µM N-acetyl-serotonin to cross the red blood cell membrane and to mobilize intracellular calcium in parasites previously loaded with the fluorescent calcium indicator Fluo-3 AM. The present data represent a step forward into the understanding of the signal transduction process in the host-parasite relationship by supporting the idea that the host hormone melatonin and N-acetyl-serotonin generate IP3 and therefore mobilize intracellular Ca2+ in Plasmodium inside red blood cells.

Effects of autacoid inhibitors and of an antagonist on malaria infection in mice

The effects of p-chlorophenylalanine, an inhibitor of serotonin synthesis, indomethacin, an inhibitor of prostaglandin synthesis, cyproheptadine, a serotonin, bradykinin and histamine antagonist, were assessed separately and in combination with chloroquine (CQ) in Vom strains of Swiss albino mice (18-22 g) of either sex infected intraperitoneally with 1 x 10(7) Plasmodium yoelii nigeriensis-induced malaria. As prophylactic, these agents reduced from 31.9 ± 4.5 to 16.1 ± 8.1% the level of parasitemia relative to control but had no appreciable activity as curative agents when administered subcutaneously once daily for 4 days after 72 h of parasites innoculum in vivo. However, CQ alone and the combination of these agents with CQ in curative and prophylactic treatments significantly reduced (from 50.3 ± 5.8 to 4.9 ± 0.75%) the level of parasitemia (P < 0.05), which was taken only once 72 h after the parasites innoculum. The prophylactic result was shown to produce better results than the curative treatment. The data indicate that inhibitors and an antagonist can reduce the parasitemia load (the extent of damage and the severity of infection) as well as enhance the effects of CQ when combined with it for malaria therapy. The study reveals that the production of autacoids in established infection renders autacoid inhibitors and an antagonist ineffective for radical cure in malarial mice; however, selective inhibition of local hormones implicated in the pathological manifestations of malaria infection by autacoid inhibitors and an antagonist may be a possible pathway to reduce the severity of infection and the associated tissue damage and to enhance the efficacy of available anti-malarials.

Comparison of the diagnosis of malaria by microscopy, immunochromatography and PCR in endemic areas of Venezuela

Whole blood samples (N = 295) were obtained from different locations in Amazonas and Sucre States, in Venezuela. Malaria was diagnosed by microscopy, OptiMAL™ and polymerase chain reaction (PCR), with Plasmodium vivax, P. falciparum, and P. malariae being detected when possible. We identified 93 infections, 66 of which were caused by P. vivax, 26 by P. falciparum, and 1 was a mixed infection. No infection caused by P. malariae was detected. The sensitivity and specificity of each diagnostic method were high: 95.7 and 97.9% for microscopy, 87.0 and 97.9% for OptiMAL, and 98.0 and 100% for PCR, respectively. Most samples (72.2%) showed more than 5000 parasites/µL blood. The sensitivity of the diagnosis by microscopy and OptiMAL decreased with lower parasitemia. All samples showing disagreement among the methods were reevaluated, but the first result was used for the calculations. Parasites were detected in the 6 false-negative samples by microscopy after the second examination. The mixed infection was only detected by PCR, while the other methods diagnosed it as P. falciparum (microscopy) or P. vivax (OptiMAL) infection. Most of the false results obtained with the OptiMAL strip were related to the P. falciparum-specific band, including 3 species misdiagnoses, which could be related to the test itself or to genetic variation of the Venezuelan strains. The use of the microscopic method for malaria detection is recommended for its low cost but is very difficult to implement in large scale, population-based studies; thus, we report here more efficient methods suitable for this purpose.

Vitamin B1 and B6 in the malaria parasite: requisite or dispensable?

Vitamins are essential compounds mainly involved in acting as enzyme co-factors or in response to oxidative stress. In the last two years it became apparent that apicomplexan parasites are able to generate B vitamers such as vitamin B1 and B6 de novo. The biosynthesis pathways responsible for vitamin generation are considered as drug targets, since both provide a high degree of selectivity due to their absence in the human host. This report updates the current knowledge about vitamin B1 and B6 biosynthesis in malaria and other apicomplexan parasites. Owing to the urgent need for novel antimalarials, the significance of the biosynthesis and salvage of these vitamins is critically discussed in terms of parasite survival and their exploitation for drug development.

Increased levels of glutamate in the central nervous system are associated with behavioral symptoms in experimental malaria

Cerebral malaria (CM) is a severe complication resulting from Plasmodium falciparum infection. This condition has been associated with cognitive, behavioral and motor dysfunctions, seizures and coma. The underlying mechanisms of CM are incompletely understood. Glutamate and other metabolites such as lactate have been implicated in its pathogenesis. In the present study, we investigated the involvement of glutamate in the behavioral symptoms of CM. Seventeen female C57BL/6 mice (20-25 g) aged 6-8 weeks were infected with P. berghei ANKA by the intraperitoneal route using a standardized inoculation of 10(6) parasitized red blood cells suspended in 0.2 mL PBS. Control animals (N = 17) received the same volume of PBS. Behavioral and neurological symptoms were analyzed by the SmithKline/Harwell/Imperial College/Royal Hospital/Phenotype Assessment (SHIRPA) battery. Glutamate release was measured in the cerebral cortex and cerebrospinal fluid of infected and control mice by fluorimetric assay. All functional categories of the SHIRPA battery were significantly altered in the infected mice at 6 days post-infection (dpi) (P ≤ 0.05). In parallel to CM symptoms, we found a significant increase in glutamate levels in the cerebral cortex (mean ± SEM; control: 11.62 ± 0.90 nmol/mg protein; infected at 3 dpi: 10.36 ± 1.17 nmol/mg protein; infected at 6 dpi: 26.65 ± 0.73 nmol/mg protein; with EGTA, control: 5.60 ± 1.92 nmol/mg protein; infected at 3 dpi: 6.24 ± 1.87 nmol/mg protein; infected at 6 dpi: 14.14 ± 0.84 nmol/mg protein) and in the cerebrospinal fluid (control: 128 ± 51.23 pmol/mg protein; infected: 301.4 ± 22.52 pmol/mg protein) of infected mice (P ≤ 0.05). These findings suggest a role of glutamate in the central nervous system dysfunction found in CM.

Photodynamic antimicrobial chemotherapy (PACT) for the treatment of malaria, leishmaniasis and trypanosomiasis

A photodynamic effect occurs when photosensitiser molecules absorb light and dissipate the absorbed energy by transferring it to biological acceptors (usually oxygen), generating an excess of reactive species that are able to force cells into death pathways. Several tropical diseases present physiopathological aspects that are accessible to the application of a photosensitiser and local illumination. In addition, disease may be transmitted through infected blood donations, and many of the aetiological agents associated with tropical diseases have been shown to be susceptible to the photodynamic approach. However, there has been no systematic investigation of the application of photoantimicrobial agents in the various presentations, whether to human disease or to the disinfection of blood products or even as photo-insecticides. We aim in this review to report the advances in the photoantimicrobial approach that are beneficial to the field of anti-parasite therapy and also have the potential to facilitate the development of low-cost/high-efficiency protocols for underserved populations.

Experimental models in vaccine research: malaria and leishmaniasis

Animal models have a long history of being useful tools, not only to test and select vaccines, but also to help understand the elaborate details of the immune response that follows infection. Different models have been extensively used to investigate putative immunological correlates of protection against parasitic diseases that are important to reach a successful vaccine. The greatest challenge has been the improvement and adaptation of these models to reflect the reality of human disease and the screening of vaccine candidates capable of overcoming the challenge of natural transmission. This review will discuss the advantages and challenges of using experimental animal models for vaccine development and how the knowledge achieved can be extrapolated to human disease by looking into two important parasitic diseases: malaria and leishmaniasis.

Resistência do Plasmodium falciparum ao fansidar, quinina e tetraciclina

Descreve-se pela primeira vez uma cêpa amazônica de Plasmodium falciparum resistente ao Fansidar (pirimetamina mais sulfadoxina) e quinino mais tetraciclina simultaneamente. O paciente, com 13 anos de idade, residia há cinco anos em Ariquemes, Estado de Rondônia, na Amazônia brasileira. A infecção foi curada com dose elevada de cloroquina administrada em dose única intravenosa (IV). É evidenciado o alto valor da cloroquina na cura da malária falciparum resistente, quando administrada em doses maiores que as usadas nos esquemas convencionais de tratamento.