Search

1Limited succes of classic malaria control measures has prompted the search for vaccines and because of the epidemiological importance of P. falciparum , which is responsible for ~80% of the malaria cases globally, greater efforts have been invested in this parasite species than in P. vivax. However, progress is also being achieved in the development of P. vivax subunit vaccines. Two candidates, one based on the circumsporozoite (CS) protein and another based on the oocyst/ookinete Pv s25 protein, have been tested in phase I clinical trials. 2– 4 Recent phase I clinical trials conducted using different formulations of P. vivax CS-derived subunit vaccines based on long synthetic peptides (LSP) have indicated that such formulations are safe, well tolerated, and immunogenic in malaria-naive volunteers. Additionally, an Escherichia coli recombinant chimeric full-length molecule of the P. vivax CS has also been recently reported. Sera from individuals naturally exposed to malaria in endemic areas and from immunized mice displayed high antibody titers to the recombinant protein. This construct is also being considered as a vaccine candidate and being proposed for further clinical trials. 5 During the last few years we have been developing a P. vivax challenge model because assessing the protective efficacy of P. vivax malaria vaccines requires a safe, reliable, and reproducible method of infecting human volunteers with sporozoites.

Malaria infection induces antibodies capable of suppressing the infectivity of gametocytes and gametes, however, little is known about the duration of the antibody response, the parasite specificity, and the role of complement. We report the analyses of the transmission-blocking (TB) activity of sera collected from 105 Plasmodium vivax-infected and 44 non-infected individuals from a malaria endemic region of Colombia, using a membrane feeding assay in Anopheles albimanus mosquitoes. In infected donors we found that TB activity was antibody dose dependent (35%), lasted for 2-4 months after infection, and in 70% of the cases different P. vivax wild isolates displayed differential susceptibility to blocking antibodies. Additionally, in a number of assays TB was complement-dependent. Twenty-seven percent of non-infected individuals presented TB activity that correlated with antibody titers. Studies here provide preliminary data on factors of great importance for further work on the development of TB vaccines.

Vaccine development for Plasmodium vivax malaria is underway. A model to assess the protective efficacy of vaccine candidates in humans is urgently needed. Given the lack of continuous P. vivax cultures, we developed a system to infect Anopheles albimanus mosquitoes using blood from P. vivax-infected patients and determined parameters for challenge of malaria-naive volunteers by mosquito bite. Absence of co-infections in parasitized blood was confirmed by tests consistent with blood bank screening. A total of 119 experiments were conducted using batches of 900–4,500 mosquitoes fed by an artificial membrane feeding method. Optimal conditions for mosquito probing and infection were determined. Presence of oocyst and sporozoites were assessed on Days 7–8 and 14–15, respectively, and conditions to choose batches of infected mosquitoes for sporozoite challenge were established. Procedures to infect volunteers took a 2-hour period including verification of inoculum dose. Anopheles albimanus mosquitoes represent a valuable resource for P. vivax sporozoite challenge of volunteers.

Randomly amplified polymorphic DNA (RAPD) analysis was performed to infer the magnitude and pattern of genetic differentiation among Lutzomyia (Nyssomyia) intermedia populations from two ecologic regions in southeast Brazil where transmission of American cutaneous leishmaniasis (ACL) by L. (Viannia) braziliensis reflects distinct eco-epidemiologic features. Two hundred thirty-five bands from six primers were analyzed for genetic variation within and between sand fly populations. A lower level of intrapopulational variability was found in domestic sand flies (compared with the peridomestic population). Gene flow FST estimates indicated homogeneity in the studied population, with limited population substructuring, but with a tendency of sand fly vectors to form clusters by micro-habitat (domestic and peridomestic). The level of genetic structuring of Lu. intermedia population from each ecologic region is distinct and may reflect association or independence between the domestic and the peridomestic habitats in rural and periurban areas, respectively, both reflecting distinct characteristics of the transmission cycle of ACL.

Plasmodium vivax transmission-blocking activity was assessed in sera from acutely infected patients from a malaria-endemic area in Colombia. We measured reduction in the number of oocysts that developed in the midguts of Anopheles albimanus mosquitoes artificially fed with blood from these patients. Of 88 mosquito batches that developed infections when parasites were mixed with normal AB human serum, one-third (36.4%) showed full transmission-blocking activity (>or= 90% inhibition) when mixed with autologous sera, 29.6% showed partial activity (50-89%), 17.0% did not block transmission (0-50%), and 17% did not enhance transmission. Transmission-blocking activity correlated with antibody titer by an immunofluorescent antibody test and decreased with the serial dilution of the sera. This activity disappeared at a 1:4 dilution in most sera tested. Afro-Colombian individuals showed lower activity than other ethnic groups and febrile patients produced stronger inhibition than those without fever.

Sycorax confusa sp. nov. is described from the Atlantic Forest of the state of Espírito Santo, Brazil. The new species has a paramere with a long bristle, a characteristic that had only been observed in Sycorax longispinosa Bravo, 2007 from the Brazilian Amazon; the new species can be differentiated from the last one because the middle acute internal projections of each paramere do not cross each other and because the anterior end of aedeagal apodeme is bulbous. A key to the species of Sycorax Haliday in Curtis, 1839 (males) from the Neotropical Region is provided.

Lutzomyia longipalpis (Diptera: Psychodidae) is the principal vector of American visceral leishmaniasis. Several studies have indicated that the Lu. longipalpis population structure is complex. It has been suggested that genetic divergence caused by genetic drift, selection, or both may affect the vectorial capacity of Lu. longipalpis. However, it remains unclear whether genetic differences among Lu. longipalpis populations are directly implicated in the transmission features of visceral leishmaniasis. We evaluated the genetic composition and the patterns of genetic differentiation among Lu. longipalpis populations collected from regions with different patterns of transmission of visceral leishmaniasis by analyzing the sequence variation in the mitochondrial cytochrome b gene. Furthermore, we investigated the temporal distribution of haplotypes and compared our results with those obtained in a previous study. Our data indicate that there are differences in the haplotype composition and that there has been significant differentiation between the analyzed populations. Our results reveal that measures used to control visceral leishmaniasis might have influenced the genetic composition of the vector population. This finding raises important questions concerning the epidemiology of visceral leishmaniasis, because these differences in the genetic structures among populations of Lu. longipalpis may have implications with respect to their efficiency as vectors for visceral leishmaniasis.

In this study, we sought to identify sand fly vectors of the Leishmania species that circulate in distinct eco-epidemiological disease-endemic rural areas within the Espirito Santo State in southeastern Brazil. PCR amplification of a conserved region of the minicircle kDNA was used to estimate infection rates in field-captured, peridomestic female sand flies. Only 13 of the 1689 female sand fly specimens (0.77%) actually contained Leishmania DNA. Leishmania braziliensis infections were found in Lutzomyia intermedia and Lu. whitmani, and, for the first time, in Lu. fischeri and Lu. ferreirana. Interestingly, the high rate of genetic polymorphism of the L. braziliensis parasites in one of the disease-endemic areas that were studied may reflect specific transmission cycles involving different sand fly vectors.

Artificial membrane feeding (AMF) assays are used to determine malaria transmission-blocking activity in Anopheles. The purpose of this study was to determine the effect of the most widely used anticoagulants, EDTA and heparin, on development of the Plasmodium vivax sporogonic cycle. Blood samples collected from 60 patients carrying P. vivax infections were used to feed An. albimanus using AMF. Seven days after feeding, mosquitoes were dissected to assess mosquito infection. Mosquitoes fed with blood containing EDTA showed a lower mean oocyst number as compared with those fed blood with heparin. However, this effect was minimized upon reduction of EDTA concentrations in the serum. This result may be explained by the fact that microgametocytes require Ca(2+), Mn(2+), and Mg(+2) to activate enzymes important for exflagellation process and for motility of ookinetes. We therefore recommend that heparin be used as the anticoagulant of choice for blood used in AMF assays.