Structural and immunological basis of cross-reactivity between dengue and Zika infections: Implications in serosurveillance in endemic regions

Dengue and Zika are arthropod-borne viral diseases present in more than 100 countries around the world. In the past decade, Zika emerged causing widespread outbreaks in new regions, where dengue has been endemic-epidemic for a long period. The wide and extensive dissemination of the mosquito vectors, Aedes aegypti, and Ae. albopictus, favor the co-existence of both infections in the same regions. Together with an important proportion of asymptomatic infections, similar clinical manifestations, and a short time window for acute infection confirmatory tests, it is difficult to differentially estimate both dengue and Zika incidence and prevalence. DENV and ZIKV flavivirus share high structural similarity, inducing a cross-reactive immune response that leads to false positives in serological tests particularly in secondary infections. This results in overestimation of recent Zika outbreaks seroprevalence in dengue endemic regions. In this review, we address the biological basis underlying DENV and ZIKV structural homology; the structural and cellular basis of immunological cross reactivity; and the resulting difficulties in measuring dengue and Zika seroprevalence. Finally, we offer a perspective about the need for more research to improve serological tests performance.

Three highly variable genome regions of the four dengue virus serotypes can accurately recapitulate the CDS phylogeny

The circulation of the four-dengue virus (DENV) serotypes has significantly increased in recent years, accompanied by an increase in viral genetic diversity. In order to conduct disease surveillance and understand DENV evolution and its effects on virus transmission and disease, efficient and accurate methods for phylogenetic classification are required. Phylogenetic analysis of different viral genes sequences is the most used method, the envelope gene (E) being the most frequently selected target. We explored the genetic variability of the four DENV serotypes throughout their complete coding sequence (CDS) of sequences available in GenBank and used genomic regions of different variability rate to recapitulate the phylogeny obtained with the DENV CDS. Our results indicate that the use of high or low variable regions accurately recapitulate the phylogeny obtained with CDS of sequences from different DENV genotypes. However, when analyzing the phylogeny of a single genotype, highly variable regions performed better in recapitulating the distance branch length, topology, and support of the CDS phylogeny. The use of three concatenated highly variable regions was not statistically different in distance branch length and support to that obtained in CDS phylogeny.•This study demonstrated the ability of highly variable regions of the DENV genome to recapitulate the phylogeny obtained with the full coding sequence (CDS).•The use of genomic regions of high or low variability did not affect the performance in recapitulating the phylogeny obtained with CDS from different genotypes. However, when phylogeny was analyzed for sequences from a single genotype, highly variable regions performed better in recapitulating the distance branch length, topology, and support of the CDS phylogeny.•The use of concatenated highly variable genome regions represent a useful option for recapitulating genome-wide phylogenies in analyses of sequences belonging to the same DENV genotype.

Genetic diversity and spatiotemporal dynamics of DENV-1 and DENV-2 infections during the 2012-2013 outbreak in Mexico

Dengue fever is caused by four related dengue virus serotypes, DENV-1 to DENV-4, where each serotype comprises distinct genotypes and lineages. The last major outbreak in Mexico occurred during 2012 and 2013, when 112,698 confirmed cases were reported (DENV-1 and DENV-2 were predominant). Following partial E, NS2A and NS5 gene sequencing, based on the virus genome variability, we analyzed 396 DENV-1 and 248 DENV-2 gene sequences from serum samples from dengue acute clinical cases from 13 Mexican states, Mutations were identified, and their genetic variability estimated, along with their evolutionary relationship with DENV sequences sampled globally. DENV-1 genotype V and DENV-2 Asian-American genotype V were the only genotypes circulating during the outbreak. Mutations in NS2A and NS5 proteins were widely disseminated and suggested local emergence of new lineages. Phylogeographic analysis suggested viral spread occurred from coastal regions, and tourist destinations, such as Yucatan and Quintana Roo, which played important roles in disseminating these lineages.

Genetic Diversity and Spatiotemporal Dynamics of Chikungunya Infections in Mexico during the Outbreak of 2014-2016

Chikungunya virus (CHIKV) is an alphavirus transmitted by Aedes mosquitoes, which causes Chikungunya fever. Three CHIKV genotypes have been identified: West African, East-Central-South African and Asian. In 2014, CHIKV was detected for the first time in Mexico, accumulating 13,569 confirmed cases in the following three years. Studies on the molecular diversification of CHIKV in Mexico focused on limited geographic regions or investigated only one structural gene of the virus. To describe the dynamics of this outbreak, we analyzed 309 serum samples from CHIKV acute clinical cases from 15 Mexican states. Partial NSP3, E1, and E2 genes were sequenced, mutations were identified, and their genetic variability was estimated. The evolutionary relationship with CHIKV sequences sampled globally were analyzed. Our sequences grouped with the Asian genotype within the Caribbean lineage, suggesting that the Asian was the only circulating genotype during the outbreak. Three non-synonymous mutations (E2 S248F and NSP3 A437T and L451F) were present in our sequences, which were also identified in sequences of the Caribbean lineage and in one Philippine sequence. Based on the phylogeographic analysis, the viral spread was reconstructed, suggesting that after the introduction through the Mexican southern border (Chiapas), CHIKV dispersed to neighboring states before reaching the center and north of the country through the Pacific Ocean states and Quintana Roo. This is the first viral phylogeographic reconstruction in Mexico characterizing the CHIKV outbreak across the country.

Prediction of neuropeptide precursors and differential expression of adipokinetic hormone/corazonin-related peptide, hugin and corazonin in the brain of malaria vector Nyssorhynchus albimanus during a Plasmodium berghei infection

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We describe precursors that predicted at least sixty neuropeptides in Ny. albimanus.

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At least 16 precursors are encoded in the Ny. albimanus brain.

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Myosuppressin neuropeptide precursor was identified in Ny albimanus.

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acp and hugin transcripts increased in Ny. albimanus brains infected with P. berghei.

Insect neuropeptides, play a central role in the control of many physiological processes. Based on an analysis of Nyssorhynchus albimanus brain transcriptome a neuropeptide precursor database of the mosquito was described. Also, we observed that adipokinetic hormone/corazonin-related peptide (ACP), hugin and corazonin encoding genes were differentially expressed during Plasmodium infection. Transcriptomic data from Ny. albimanus brain identified 29 pre-propeptides deduced from the sequences that allowed the prediction of at least 60 neuropeptides. The predicted peptides include isoforms of allatostatin C, orcokinin, corazonin, adipokinetic hormone (AKH), SIFamide, capa, hugin, pigment-dispersing factor, adipokinetic hormone/corazonin-related peptide (ACP), tachykinin-related peptide, trissin, neuropeptide F, diuretic hormone 31, bursicon, crustacean cardioactive peptide (CCAP), allatotropin, allatostatin A, ecdysis triggering hormone (ETH), diuretic hormone 44 (Dh44), insulin-like peptides (ILPs) and eclosion hormone (EH). The analysis of the genome of An. albimanus and the generated transcriptome, provided evidence for the identification of myosuppressin neuropeptide precursor. A quantitative analysis documented increased expression of precursors encoding ACP peptide, hugin and corazonin in the mosquito brain after Plasmodium berghei infection. This work represents an initial effort to characterize the neuropeptide precursors repertoire of Ny. albimanus and provides information for understanding neuroregulation of the mosquito response during Plasmodium infection.

Determination of insecticides' lethal concentrations and metabolic enzyme levels in Triatoma dimidiata

OBJECTIVE

The feasibility of the use of WHO impregnated paper and biochemical assays to determine lethal concentrations (LC50 and LC99) and insecticide metabolic enzyme levels of Triatoma dimidiata.

MATERIALS AND METHODS

LC50 and LC99 were calculated with WHO papers impregnated at different concentrations of malathion, propoxur and deltamethrin; the percentage of insensitive acetylcholinesterase (iAChE); and the levels of esterases, glutathione S-transferases, and monooxygenases in laboratory nymphs of the first stage (5 to 7 days), were undertaken using the WHO biochemical assays.

RESULTS

Respectively the LC50 and LC99 μg/cm2 obtained for malathion were 43.83 and 114.38, propoxur 4.71 and 19.29, and deltamethrin 5.80 and 40.46. A 30% of the population had an iAChE, and only a few individuals had high P450 and β-eterase levels.

CONCLUSIONS

Impregnated papers and biochemical tests developed by WHO for other insects, proved to be feasible methods in monitoring insecticide resistance and metabolic enzymes involved in T. dimidiata.

Molecular variation of Plasmodium vivax dehydrofolate reductase in Mexico and Nicaragua contrasts with that occurring in South America

OBJECTIVE

To research mutations associated to pyrimethamine resistance in dihydrofolate reductase (pvdhfr) of Plasmodium vivax from Mexico and Nicaragua and compare it to that reported in the rest of America.

MATERIALS AND METHODS

Genomic DNA was obtained from P. vivax-infected blood samples. A pvdhfr gene fragment was amplified and sequenced. The identified gene variations were compared to those observed in other affected sites of America.

RESULTS

No mutations in pvdhfr were detected in P. vivax from Mexico and Nicaragua. One synonymous change and variation in the repeat domain was detected in Nicaraguan parasites. In South America, a high frequency of variant residues 58R and 117N associated to pyrimethamine resistance was reported.

CONCLUSIONS

The lack of polymorphisms associated with pyrimethamine resistance suggests that drug-resistant P. vivax has not penetrated Mesoamerica, nor have local parasites been under selective pressure. These data contribute to establish the basis for the epidemiological surveillance of drug resistance.

Ookinete-Specific Genes and 18S SSU rRNA Evidenced in Plasmodium vivax Selection and Adaptation by Sympatric Vectors

In the southern Pacific coast of Chiapas, Mexico (SM), the two most abundant vector species, Nyssorhynchus albimanus and Anopheles pseudopunctipennis, were susceptible to different Plasmodium vivax Pvs25/28 haplotypes. To broaden our understanding of the existing P. vivax in the area, genes encoding proteins relevant for ookinete development and the 18S rRNA were studied. P. vivax infectivity (percentage of infected mosquitoes and oocyst numbers) was evaluated by simultaneously feeding infected blood samples from patients to Ny. albimanus and An. pseudopunctipennis female mosquitoes. Three infectivity patterns were identified: one group of parasites were more infective to An. pseudopunctipennis than to Ny. albimanus, another group was more infective to Ny. albimanus, while a third group infected both vectors similarly. In 29 parasite isolates, the molecular variations of ookinete-specific genes and the 18S rRNA-type S were analyzed. Using concatenated sequences, phylogenetic trees, and Structure analysis, parasite clustering within SM isolates and between these and those from other geographical origins were investigated. A ML phylogenetic tree resolved two parasite lineages: PvSM-A and PvSM-B. They were associated to a different 18S rRNA variant. PvSM-A parasites had 18S rRNA variant rV2 and correspond to parasites causing high oocyst infection in Ny. albimanus. A new ML tree and Structure analysis, both comprising global sequences, showed PvSM-A clustered with Latin American parasites. Meanwhile, all isolates of PvSM-B had 18S rRNA variant rV1 and remained as unique genetic cluster comprising two subgroups: PvSM-Ba, producing high infection in An. pseudopunctipennis, and PvSM-Bb, causing similar oocyst infection in both vector species. PvSM-A parasites were genetically similar to parasites from South America. Meanwhile, PvSM-B were exclusive to southern Mexico and share ancestry with Asian parasites. The results suggest that these lineages evolved separately, likely by geographic and vector restriction.

Glycosylation on proteins of the intestine and perimicrovillar membrane of Triatoma (Meccus) pallidipennis, under different feeding conditions

Trypanosoma cruzi, the causative agent of Chagas disease, interacts with molecules in the midgut of its insect vector to multiply and reach the infective stage. Many studies suggest that the parasite binds to midgut-specific glycans. We identified several glycoproteins expressed in the intestine and perimicrovillar membrane (PMM) of Triatoma (Meccus) pallidipennis under different feeding conditions. In order to assess changes in protein-linked glycans, we performed lectin and immunoblot analyses on glycoprotein extracts from these intestinal tissues using well-characterized lectins, and an antibody, which collectively recognize a wide range of different glycans epitopes. We observed that the amount and composition of proteins and glycoproteins associated with different glycans structures changed over time in the intestines and PMM under different physiological conditions. PMM extracts contained a wide variety of glycoproteins with different sugar residues, including abundant high-mannose and complex sialylated glycans. We propose that these molecules could be involved in the process of parasite-vector interactions.

Plasmodium vivax CSP-Pvs25 variants from southern Mexico produce distinct patterns of infectivity for Anopheles albimanus versus An. pseudopunctipennis, in each case independent of geographical origin

BACKGROUND

The susceptibility of Anopheles albimanus and An. pseudopunctipennis to local Plasmodium vivax has been associated in southern Mexico with two ookinete surface proteins (Pvs25/28) polymorphism. Perhaps parasite population selection (i.e. adaptation to local vectors) contributes to this phenomenon. It is also possible that certain molecular interactions exist between P. vivax and each mosquito species independently of geographical origin. This study aimed to explore the susceptibility of An. albimanus and An. pseudopunctipennis (collected from different geographical sites) to P. vivax cspVk/Pvs25-130 haplotypes from southern Mexico.

RESULTS

Of the 120 P. vivax-infected blood samples used to simultaneously feed An. albimanus and An. pseudopunctipennis mosquitoes originating from various geographical sites, 80 produced at least one infected mosquito species. Three parasite haplotypes were identified in infected blood: Vk210/Pvs25-A (12.5%), Vk210/Pvs25-B (20%) and Vk247/Pvs25-B (67.5%). Two parameters (the proportion of infected mosquitoes and number of oocysts/mosquito) showed a similar pattern for each mosquito species (independently of geographical origin). For An. albimanus mosquitoes (from the Pacific coast, Mexican gulf and Lacandon Forest lowlands), these two parameters were higher in specimens infected with P. vivax Vk210/Pvs25-A versus Vk210/Pvs25-B or Vk247/Pvs25-B (P < 0.001). For An. pseudopunctipennis mosquitoes (from the Pacific coast, northeast Mexico and east Guatemala foothills), the same two parameters were higher in specimens infected with Vk247/Pvs25-B or Vk210/Pvs25-B versus Vk210/Pvs25-A (P < 0.001). Higher infection rates were caused by Vk247/Pvs25-B than Vk210/Pvs25-B parasites in An. pseudopunctipennis (P = 0.011) and An. albimanus (P = 0.001). The greatest parasitaemia, gametocytaemia and microgamete formation was observed in Vk247/Pvs25-B infected blood, and each of these parameters correlated with each other and with the number of oocysts in An. pseudopunctipennis from the sympatric colony.

CONCLUSIONS

Plasmodium vivax Vk247/Pvs25-B infections were the most prevalent, likely due to the higher parasitaemia produced in the susceptible vector (especially An. pseudopunctipennis). The analysis of mosquito-parasite interactions indicate that An. pseudopunctipennis and An. albimanus each have a unique pattern of transmitting genetic variants of P. vivax, and this is not dependent on geographical origin. The present findings highlight the importance of parasite genotyping to understand transmission dynamics and vectorial participation.

Participation of 14-3-3ε and 14-3-3ζ proteins in the phagocytosis, component of cellular immune response, in Aedes mosquito cell lines

BACKGROUND

Better knowledge of the innate immune system of insects will improve our understanding of mosquitoes as potential vectors of diverse pathogens. The ubiquitously expressed 14-3-3 protein family is evolutionarily conserved from yeast to mammals, and at least two isoforms of 14-3-3, the ε and ζ, have been identified in insects. These proteins have been shown to participate in both humoral and cellular immune responses in Drosophila. As mosquitoes of the genus Aedes are the primary vectors for arboviruses, causing several diseases such as dengue fever, yellow fever, Zika and chikungunya fevers, cell lines derived from these mosquitoes, Aag-2 from Aedes aegypti and C6/36 HT from Aedes albopictus, are currently used to study the insect immune system. Here, we investigated the role of 14-3-3 proteins (ε and ζ isoform) in phagocytosis, the main cellular immune responses executed by the insects, using Aedes spp. cell lines.

RESULTS

We evaluated the mRNA and protein expression of 14-3-3ε and 14-3-3ζ in C6/36 HT and Aag-2 cells, and demonstrated that both proteins were localised in the cytoplasm. Further, in C6/36 HT cells treated with a 14-3-3 specific inhibitor we observed a notable modification of cell morphology with filopodia-like structure caused through cytoskeleton reorganisation (co-localization of 14-3-3 proteins with F-actin), more importantly the decrease in Salmonella typhimurium, Staphylococcus aureus and E. coli phagocytosis and reduction in phagolysosome formation. Additionally, silencing of 14-3-3ε and 14-3-3ζ expression by mean of specific DsiRNA confirmed the decreased phagocytosis and phagolysosome formation of pHrodo labelled E. coli and S. aureus bacteria by Aag-2 cells.

CONCLUSION

The 14-3-3ε and 14-3-3ζ proteins modulate cytoskeletal remodelling, and are essential for phagocytosis of Gram-positive and Gram-negative bacteria in Aedes spp. cell lines.

Lys48 ubiquitination during the intraerythrocytic cycle of the rodent malaria parasite, Plasmodium chabaudi

Ubiquitination tags proteins for different functions within the cell. One of the most abundant and studied ubiquitin modification is the Lys48 polyubiquitin chain that modifies proteins for their destruction by proteasome. In Plasmodium is proposed that post-translational regulation is fundamental for parasite development during its complex life-cycle; thus, the objective of this work was to analyze the ubiquitination during Plasmodium chabaudi intraerythrocytic stages. Ubiquitinated proteins were detected during intraerythrocytic stages of Plasmodium chabaudi by immunofluorescent microscopy, bidimensional electrophoresis (2-DE) combined with immunoblotting and mass spectrometry. All the studied stages presented protein ubiquitination and Lys48 polyubiquitination with more abundance during the schizont stage. Three ubiquitinated proteins were identified for rings, five for trophozoites and twenty for schizonts. Only proteins detected with a specific anti- Lys48 polyubiquitin antibody were selected for Mass Spectrometry analysis and two of these identified proteins were selected in order to detect the specific amino acid residues where ubiquitin is placed. Ubiquitinated proteins during the ring and trophozoite stages were related with the invasion process and in schizont proteins were related with nucleic acid metabolism, glycolysis and protein biosynthesis. Most of the ubiquitin detection was during the schizont stage and the Lys48 polyubiquitination during this stage was related to proteins that are expected to be abundant during the trophozoite stage. The evidence that these Lys48 polyubiquitinated proteins are tagged for destruction by the proteasome complex suggests that this type of post-translational modification is important in the regulation of protein abundance during the life-cycle and may also contribute to the parasite cell-cycle progression.

IDENTIFICATION AND EXPRESSION ANALYSIS OF TWO 14-3-3 PROTEINS IN THE MOSQUITO Aedes aegypti, AN IMPORTANT ARBOVIRUSES VECTOR

The 14-3-3 proteins are evolutionarily conserved acidic proteins that form a family with several isoforms in many cell types of plants and animals. In invertebrates, including dipteran and lepidopteran insects, only two isoforms have been reported. 14-3-3 proteins are scaffold molecules that form homo- or heterodimeric complexes, acting as molecular adaptors mediating phosphorylation-dependent interactions with signaling molecules involved in immunity, cell differentiation, cell cycle, proliferation, apoptosis, and cancer. Here, we describe the presence of two isoforms of 14-3-3 in the mosquito Aedes aegypti, the main vector of dengue, yellow fever, chikungunya, and zika viruses. Both isoforms have the conserved characteristics of the family: two protein signatures (PS1 and PS2), an annexin domain, three serine residues, targets for phosphorylation (positions 58, 184, and 233), necessary for their function, and nine alpha helix-forming segments. By sequence alignment and phylogenetic analysis, we found that the molecules correspond to Ɛ and ζ isoforms (Aeae14-3-3ε and Aeae14-3-3ζ). The messengers and protein products were present in all stages of the mosquito life cycle and all the tissues analyzed, with a small predominance of Aeae14-3-3ζ except in the midgut and ovaries of adult females. The 14-3-3 proteins in female midgut epithelial cells were located in the cytoplasm. Our results may provide insights to further investigate the functions of these proteins in mosquitoes.

An antibody against an Anopheles albimanus midgut myosin reduces Plasmodium berghei oocyst development

Background

Malaria parasites are transmitted by Anopheles mosquitoes. Although several studies have identified mosquito midgut surface proteins that are putatively important for Plasmodium ookinete invasion, only a few have characterized these protein targets and demonstrated transmission-blocking activity. Molecular information about these proteins is essential for the development of transmission-blocking vaccines (TBV). The aim of the present study was to test three monoclonal antibodies (mAbs), A-140, A-78 and A-10, for their ability to recognize antigens and block oocyst infection of the midgut of Anopheles albimanus, a major malaria vector in Latin America.

Method

Western-blot of mAbs on antigens from midgut brush border membrane vesicles was used to select antibodies. Three mAbs were tested by membrane feeding assays to evaluate their potential transmission-blocking activity against Plasmodium berghei. The cognate antigens recognized by mAbs with oocyst-reducing activity were determined by immunoprecipitation followed by liquid chromatography tandem mass spectrometry.

Results

Only one mAb, A-140, significantly reduced oocyst infection intensity. Hence, its probable protein target in the Anopheles albimanus midgut was identified and characterized. It recognized three high-molecular mass proteins from a midgut brush border microvilli vesicle preparation. Chemical deglycosylation assays confirmed the peptide nature of the epitope recognized by mAb A-140. Immunoprecipitation followed by proteomic identification with tandem mass spectrometry revealed five proteins, presumably extracted together as a complex. Of these, AALB007909 had the highest mascot score and corresponds to a protein with a myosin head motor domain, indicating that the target of mAb A-140 is probably myosin located on the microvilli of the mosquito midgut.

Conclusion

These results provide support for the participation of myosin in mosquito midgut invasion by Plasmodium ookinetes. The potential inclusion of this protein in the design of new multivalent vaccine strategies for blocking Plasmodium transmission is discussed.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1548-8) contains supplementary material, which is available to authorized users.

Morphological and proteomic characterization of midgut of the malaria vector Anopheles albimanus at early time after a blood feeding

The midgut of anopheline mosquito is the entry of Plasmodium, the causative agent of malaria.When the mosquito feeds on parasite infected host, Plasmodium parasites reach the midgut and must confront digestive enzymes, the innate immune response and go across the peritrophic matrix (PM), a thick extracellular sheath secreted by the mosquito midgut epithelial cells. Then, to continue its development, the parasite must reach the salivary glands to achieve transmission to a vertebrate host. We report here the morphological and biochemical descriptions of the midgut changes after a blood meal in Anopheles albimanus. Before blood feeding, midgut epithelial cells contained numerous electrondense vesicles distributed in the central to apical side. These vesicles were secreted to the luminal side of the midgut after a blood meal. At early times after blood ingest, the PM is formed near microvilli as a granulous amorphous material and after it consolidates forming a highly organized fibrillar structure, constituted by layers of electrondense and electronlucent regions. Proteomic comparative analysis of sugar and blood fed midguts showed several molecules that modify their abundance after blood intake; these include innate immunity, cytoskeletal, stress response, signaling, and digestive, detoxifying and metabolism enzymes. Biological significance In the midgut of mosquitoes during bloodfeeding, many simultaneous processes occur, including digestion, innate immune activities, cytoskeleton modifications, construction of a peritrophic matrix and hormone production, between others. Mechanical forces are very intense during bloodfeeding and epithelial and muscular cells must resist the stress, modifying the actin cytoskeleton and coordinating intracellular responses by signaling. Microorganisms present in midgut contents reproduce and interact with epithelial cells triggering innate immune response. When infectious agents are present in the blood meal they must traverse the peritrophic matrix, an envelope formed from secretion products of epithelial cells, and evade the immune system in order to reach the epithelium and continue their journey towards salivary glands, in preparation for the transmission to the new hosts. During all these processes, proteins of mosquitoes are modified in order to deal with mechanical and biological challenges, and the aim of this work is to study these changes.

Diferential DNA synthesis in Anopheles albimanus tissues induced by immune challenge with different microorganisms

The induction of DNA synthesis in various tissues of Anopheles albimanus, in response to challenge with Saccharomyces cerevisiae, Micrococcus luteus, and Serratia marcescens, was analyzed by 5-bromo-2-deoxy-uridine (BrdU) incorporation. Microorganism-inoculated mosquitoes were fed with a sucrose solution containing BrdU and maintained alive for 5 days. Alternatively, abdominal carcasses of microorganisms-inoculated mosquitoes were cultivated in Roswell Park Memorial Institute (RPMI) medium supplemented with BrdU for 5 days. Control groups were inoculated with RPMI alone. In both experiments, DNA synthesis, evidenced by epifluorescence with an anti-BrdU fluorescein-labeled antibody, occurred in fat body, epithelial cells of pleural membranes, dorsal vessel, and the oviducts. Relative quantification of DNA synthesis, evaluated by ELISA using an anti-BrdU peroxidase-labeled antibody, was higher in abdomen tissues of microorganisms-inoculated mosquitoes than controls in in vitro and in vivo experiments. The intensity of DNA synthesis varied among the different microorganism challenges, but was higher in in vivo experiments, compared to cultured samples. These differences in DNA synthesis suggest a compartmentalization of the immune response, probably mediated by different signaling pathways.

Molecular epidemiology of Plasmodium vivax in Latin America: polymorphism and evolutionary relationships of the circumsporozoite gene

Background

The origins and dispersal of Plasmodium vivax to its current worldwide distribution remains controversial. Although progress on P. vivax genetics and genomics has been achieved worldwide, information concerning New World parasites remains fragmented and largely incomplete. More information on the genetic diversity in Latin America (LA) is needed to better explain current patterns of parasite dispersion and evolution.

Methods

Plasmodium vivax circumsporozoite protein gene polymorphism was investigated using polymerase chain reaction amplification and restriction fragment length polymorphism (PCR-RFLP), and Sanger sequencing in isolates from the Pacific Ocean coast of Mexico, Nicaragua, and Peru. In conjunction with worldwide sequences retrieved from the Genbank, mismatch distribution analysis of central repeat region (CRR), frequency estimation of unique repeat types and phylogenetic analysis of the 3′ terminal region, were performed to obtain an integrative view of the genetic relationships between regional and worldwide isolates.

Results

Four RFLP subtypes, vk210a, b, c and d were identified in Southern Mexico and three subtypes vk210a, e and f in Nicaragua. The nucleotide sequences showed that Mexican vk210a and all Nicaraguan isolates were similar to other American parasites. In contrast, vk210b, c and d were less frequent, had a domain ANKKAEDA in their carboxyl end and clustered with Asian isolates. All vk247 isolates from Mexico and Peru had identical RFLP pattern. Their nucleotide sequences showed two copies of GGQAAGGNAANKKAGDAGA at the carboxyl end. Differences in mismatch distribution parameters of the CRR separate vk247 from most vk210 isolates. While vk247 isolates display a homogeneous pattern with no geographical clustering, vk210 isolates display a heterogeneous geographically clustered pattern which clearly separates LA from non-American isolates, except vk210b, c and d from Southern Mexico.

Conclusions

The presence of vk210a in Mexico and vk210e, f and g in Nicaragua are consistent with other previously reported LA isolates and reflect their circulation throughout the continent. The vk210b, c and d are novel genotypes in LA. Their genetic relationships and low variability within these vk210 and/or within the vk247 parasites in Southern Mexico suggest its recent introduction and/or recent expansion to this region. The global analysis of P. vivax csp suggests this parasite introduction to the region and likely LA by different independent events.

Antimicrobial properties of Anopheles albimanus pericardial cells

Insect pericardial cells (PCs) are strategically located along the dorsal vessel where they encounter a high hemolymph flow enabling them to undertake their osmoregulatory, detoxifying, and scavenging functions. In this location, PCs also encounter foreign molecules and microorganisms. The response of PCs of the mosquito Anopheles albimanus, one of the most important Plasmodium vivax vectors in Mexico and Latin America, to Saccharomyces cerevisiae was analyzed by using biochemical, cellular, ultrastructural, and bioinformatics approaches. Immune gene transcripts were identified in the PC transcriptome of A. albimanus. PCs responded to the presence of yeast and zymosan with increased lysosomal and phosphatase activities and produced lytic activity against bacteria. Our results indicate that mosquito PCs play a key role in the neutralization and elimination of pathogens.

Plasmodium berghei ookinetes glide and release Pbs25 and circumsporozoite thrombospondin-related protein on solid surface substrata

Plasmodium spp. development within mosquito vectors includes invasive ookinete and sporozoites stages, which display gliding movements during invasion of the midgut and salivary glands, respectively. Sporozoite gliding has been well documented, and several proteins released during sporozoite's locomotion have been described. However, proteins on the ookinete gliding trails are poorly described. In the present study, we documented that 2 proteins, Pbs25 and circumsporozoite thrombospondin-related protein (CTRP), are released during Plasmodium berghei ookinete gliding on a solid surface substrate.

[Biotechnological advances in infectious diseases diagnosis]

The detection of molecules of pathogens (antigens and genetic material) and host molecules in response to infections (antibodies) is the basic principle involved in molecular diagnostic tests. These tests have avoided the need to detect the attacking pathogen. New advances in molecular biology and the development of robotic technology and genomic and protein sequencing have allowed for the development of new high performance and highly specific tests. Genomics and proteomics contribute to the identification of biomarkers and biotechnology provides methods to produce high purity reagents. The identification of coding genes of specific antigens, their cloning and recombinant production, the production of monoclonal antibodies, their fragments and single chain antibodies enabled new, safer, high sensitivity and specificity immunological techniques to develop. New recognition molecules, including aptamers, will soon replace the need to produce antibodies by immunization. For the detection of genetic material, new methodological strategies based on hybridization and amplification (PCR, end point and real time) in multiplex and microarray formats have been developed, and for their detection new reporter molecules have been designed that enable their quantification. Although these methods require sophisticated instrumentation, they will soon be accessible for application in public health.

Prostaglandin E2 modulates the expression of antimicrobial peptides in the fat body and midgut of Anopheles albimanus

Prostaglandins (PGs) participate in the regulation of vertebrate and in at least six insect orders' immune responses. We identified PGE2 in midgut, fat body, Malpighian tubules, and ovarioles of Anopheles albimanus (Aa) mosquitoes. Our data indicate that PGE2 synthesis in cultured midguts responds to the presence of two bacterial species, Micrococcus luteus and Klebsiella pneumoniae. The production of mRNA coding for antimicrobial peptides Aa-Attacin, Aa-Cecropin, and Aa-Gambicin was observed in cultured fat bodies and midguts. The production of these messengers was reduced in the presence of dexamethasone, and this effect was reversed by arachidonic acid. Adding PGE2 to cultures resulted in increased Aa-cecropin mRNA and decreased Aa-attacin and Aa-gambicin mRNAs.

Cloning and functional characterization of the Anopheles albimanus DMT1/NRAMP homolog: implications in iron metabolism in mosquitoes

In addition to its wide role in metabolism, iron in insects has been implicated in vitellogenesis and the immune response. The NRAMP family comprises a well-conserved family of divalent cation transporters in metazoans. To gain insight on the role of NRAMP in Anopheles albimanus, we cloned a cDNA encoding a 571-residue protein (AnaNRAMP) with the structural features defining the NRAMP family. AnaNRAMP mRNA induced (59)Fe(2+) incorporation when injected into Xenopus oocytes. Western blot analysis revealed that AnaNRAMP is expressed in the head, midgut and at high levels in Malpighian tubules of unfed female mosquito. Upon blood feeding, AnaNRAMP levels were reduced in the midgut whereas they increased in the Malpighian tubules. Using immuno-localization by transmission electron microscopy, AnaNRAMP was localized in the membrane of the intra-cellular concretions or spherites of the Malpighian tubule principal cells. Taken together, our results suggest an important role of AnaNRAMP in iron transport and indicate a role of the mosquito Malpighian tubule as an important organ for iron homeostasis.

GP35 ANOAL, an abundant acidic glycoprotein of female Anopheles albimanus saliva

Salivary glands of female mosquitoes produce proteins, not completely described yet, that participate in carbohydrate and blood feeding. Here, we report an acidic glycoprotein of 35 kDa (GP35 ANOAL) secreted in the saliva of the malaria vector mosquito Anopheles albimanus. GP35 ANOAL is produced exclusively in the distal lateral lobes of adult female salivary glands, it has a pI of 4.45 and is negatively stained by regular silver stain. An 888 bp cDNA clone encoding a predicted product of 240 amino acids has a signal peptide, potential post-translational modification sites, and a disintegrin signature RGD. The GP35 ANOAL sequence depicts high similarities with the 30 kDa saliva allergen of Aedes aegypti, 30 kDa allergen-like hypothetical proteins, and GE-rich proteins present in several Anopheles species, as well as in Ae. albopictus and Culex pipiens quinquefasciatus. The function of this protein family is still unknown.

Attraction of gravid anopheles Pseudopunctipennis females to oviposition substrates by Spirogyra majuscula (Zygnematales: Zygnmataceae) algae under laboratory conditions

The attraction of Anopheles pseudopunctipennis gravid females to oviposition substrates containing Spirogyra majuscula algae was investigated under laboratory conditions. Gravid females deposited significantly more eggs in cups containing natural algae in water from breeding sites than in cups containing artificial (nylon rope) life-like algae in water from the corresponding natural breeding site, or in cups containing natural algae in distilled water. Bioassays with Spirogyra majuscula organic extracts indicated that these extracts at concentrations of 0.1%, 0.01%, and 0.001% attracted more oviposition, but concentrations of 1%, 10%, and 100% were repellent. Gas chromatography and mass spectrometry analysis of algae organic extracts revealed a mixture of ethyl acetate and hydrocarbons compounds. These results suggest that the attraction of gravid An. pseudopunctipennis to natural breeding sites containing filamentous algae is probably mediated by organic compounds released by the algae.

Induction of DNA synthesis in Anopheles albimanus tissue cultures in response to a Saccharomyces cerevisiae challenge

DNA synthesis was detected by the incorporation of 5-bromo-2' deoxy-uridine (BrdU) in adult Anopheles albimanus organs in culture in response to a challenge with Saccharomyces cerevisiae. Abdomens of mosquitoes inoculated with Roswell Park Memorial Institute medium (RPMI, control) or yeast were cultivated in RPMI plus ConA and BrdU for 5 days. DNA was obtained by phenolic extraction and the incorporated BrdU was quantified by ELISA using anti-BrdU peroxidase-labeled antibodies. Abdomen tissues of mosquitoes inoculated with yeast showed higher DNA synthesis than controls. Organs from untreated mosquitoes cultured in the presence of zymosan also synthesized DNA but at a lower level than tissues from yeast-inoculated mosquitoes. In similar experiments, DNA synthesis was inhibited by the addition of colchicine. DNA synthesis, evidenced by epifluorescence using an anti-BrdU fluorescein-labeled antibody, occurred in fat body, epithelial cells in pleural membranes, and the dorsal vessel. Pleural membranes showed the highest number of labeled cells. These tissues were also labeled with anti-PCNA (proliferating cell nuclear antigen) antibodies, two of which were able to produce polytene chromosomes under yeast stimulation. These results demonstrate that different An. albimanus tissues undergo DNA synthesis in response to foreign particles.

Host selection and gonotrophic cycle length of Anopheles punctimacula in southern Mexico

The host preference, survival rates, and length of the gonotrophic cycle of Anopheles punctimacula was investigated in southern México. Mosquitoes were collected in 15-day separate experiments during the rainy and dry seasons. Daily changes in the parous-nulliparous ratio were recorded and the gonotrophic cycle length was estimated by a time series analysis. Anopheles punctimacula was most abundant during the dry season and preferred animals to humans. The daily survival rate in mosquitoes collected in animal traps was 0.96 (parity rate = 0.86; gonotrophic cycle = 4 days). The length of gonotrophic cycle of 4 days was estimated on the base of a high correlation coefficient value appearing every 4 days. The minimum time estimated for developing mature eggs after blood feeding was 72 h. The proportion of mosquitoes living enough to transmit Plasmodium vivax malaria during the dry season was 0.35.

Antimalarial 4-phenylcoumarins from the stem bark of Hintonia latiflora

The EtOAc extract of the stem bark of Hintonia latiflora showed the suppression of total parasitemia and the chemosuppression of schizont numbers, when tested in vivo against Plasmodium berghei infection in mice. Bioassay-directed fractionation of the EtOAc extract, using the in vitro 16 h and the in vivo 4-day suppression tests on P. berghei schizont numbers, led to the isolation of the new compound 5-O-beta-D-glucopyranosyl-7,4'-dimethoxy-3'-hydroxy-4-phenylcoumarin (1), along with the known 5-O-beta-D-glucopyranosyl-7-methoxy-3',4'-dihydroxy-4-phenylcoumarin (2). The structure of compound 1 was established on the basis of spectroscopic data interpretation. Compounds 1 and 2 suppressed the development of P. berghei schizonts in vitro with IC50 values of 24.7 and 25.9 microM, respectively. Compound 2 suppressed the development of schizonts at the dose of 40 mg/kg by 70.8% in the in vivo assay.

Determinant factors for malaria transmission on the coast of Oaxaca State, the main residual transmission focus in Mexico

OBJECTIVE

The purpose of this study was to investigate the influence of demographic, socioeconomic and ecological factors in malaria transmission in the most important residual transmission focus in Mexico, located in the state of Oaxaca.

MATERIAL AND METHODS

The extension of the focus was determined by a spatial and time analysis of the distribution of malaria cases in the state between 1998 and 1999 using a Geographical Information System. A malaria transmission intensity index (MTII) was constructed based on the total number of cases during the study period and the duration and frequency of transmission outbreaks within the villages. The relationship between local determinants and malaria transmission intensity was investigated using multinomial and ordered logistic models.

RESULTS

The distribution of villages according to their MTII was: 325 high, 341 medium, 142 low and 717 with no transmission. Localities of high MTII were associated with areas having a tropical climate with summer rains and low water evaporation. Most high MTII villages were located in elevations between 200 and 500 m above sea level, in the area around Pochutla City. The amount of temporary streams in the neighborhood of localities had a highly significant positive association with the MTII. Distance to roads was only significant in the high malaria MTII stratum.

CONCLUSIONS

The main factors determining malaria transmission in the focus are related to good conditions for the breeding of mosquito vectors. The existence of short-range population movements around Pochutla, the main economically active city in the area, indicates the necessity to implement a system of epidemiological surveillance to halt the dispersion of new outbreaks.

Biological variation in two Anopheles vestitipennis populations with different feeding preferences in southern Mexico

The lengths of gonotrophic cycle and egg development and survival rate were studied in Anopheles vestitipennis collected in horse and human-baited traps in southern Mexico. The gonotrophic cycle duration was estimated using cross-correlation analysis, whereas the survival rate was assessed using a vertical method. Daily changes of parity rates gave significant correlation indices at 3 and 4 days in the zoophilic and anthropophilic populations, respectively. The minimum time required to develop mature eggs after blood feeding was 54 and 60 h, and the survival rate was 0.93 and 0.88 in zoophilic and anthropophilic female mosquito populations, respectively. These biological differences provide additional support for the existence of subpopulations with distinctive feeding preferences within An. vestitipennis in southern Mexico.

[Efficacy of a rapid test to diagnose Plasmodium vivax in symptomatic patients of Chiapas, Mexico]

OBJECTIVE

To evaluate, under laboratory conditions, the sensitivity and specificity of a rapid diagnostic test (OptiMAL), based on immunoreactive strips, to detect Plasmodium vivax infection in febrile patients in Southern Chiapas, Mexico.

MATERIAL AND METHODS

The presence of parasites in blood samples of 893 patients was investigated by Giemsa-stained thick blood smear microscopic examination (gold standard). A blood drop from the same sample was smeared on immunoreactive strips to investigate the presence of the parasite pLDH. Discordant results were resolved by PCR amplification of the parasite's 18S SSU rRNA, to discard infection.

RESULTS

OptiMAL had an overall sensitivity of 93.3% and its specificity was 99.5%. Its positive and negative predictive values were 96.5% and 98.9%, respectively. Signal intensity in OptiMAL strips correlated well with the parasitemia density in the blood samples (r = 0.601, p = 0.0001).

CONCLUSION

This rapid test had acceptable sensitivity and specificity to detect P. vivax under laboratory conditions and could be useful for malaria diagnosis in field operations in Mexico.

Cry11Aa toxin from Bacillus thuringiensis binds its receptor in Aedes aegypti mosquito larvae through loop alpha-8 of domain II

Bacillus thuringiensis subs israelensis produces Cry toxins active against mosquitoes. Receptor binding is a key determinant for specificity of Cry toxins composed of three domains. We found that exposed loop alpha-8 of Cry11Aa toxin, located in domain II, is an important epitope involved in receptor interaction. Synthetic peptides corresponding to exposed regions in domain II (loop alpha-8, beta-4 and loop 3) competed binding of Cry11Aa to membrane vesicles from Aedes aegypti midgut microvilli. The role of loop alpha-8 of Cry11A in receptor interaction was demonstrated by phage display and site-directed mutagenesis. We isolated a peptide-displaying phage (P5.tox), that recognizes loop alpha-8 in Cry11Aa, interferes interaction with the midgut receptor and attenuates toxicity in bioassay. Loop alpha-8 mutants affected in toxicity and receptor binding were characterized.

Immunostaining for allatotropin and allatostatin-A and -C in the mosquitoes Aedes aegypti and Anopheles albimanus

Confocal laser-scanning microscopy was used to carry out a comparative study of the immunostaining for three families of neuropeptides, viz., allatostatin-A (AS-A), allatostatin-C (AS-C) and allatotropin (AT), in adult female mosquitoes of Aedes aegypti and Anopheles albimanus. The specific patterns of immunostaining for each of the three peptides were similar in both species. The antisera raised against AT, AS-A, and AS-C revealed intense immunoreactivity in the cells of each protocerebral lobe of the brain and stained cells in each of the ventral ganglia and neuronal projections innervating various thoracic and abdominal tissues. Only the AS-A antiserum labeled immunoreactive endocrine cells in the midgut. The distribution of the peptides supports the concept that they play multiple regulatory roles in both species.

Innate host selection in Anopheles vestitipennis from southern Mexico

We assessed the degree of host specificity of the purported anthropophilic and zoophilic populations of Anopheles vestitipennis. A series of experiments were conducted in an experimental hut with 3 compartments lined with nylon netting. A central release compartment and 2 side compartments were each baited with equivalent surface area of human and animal baits. Wild An. vestitipennis collected on each host, as well as corresponding F1 mosquitoes, were released in the central compartment. Overall, 22% (166/748) of all mosquitoes collected on humans were recaptured in the human compartment, whereas 23% of mosquitoes originally collected on animals were recaptured in this compartment. Experiments with F1 females resulted in 59% human selection rates, a 2.6 times increase compared with wild anthropophilic females, while a 1.2 times decrease in human selection rates (from 24% to 20%) was observed in F1 of wild zoophilic females. Host selection experiments in the Lacandón Forest revealed the same trend. These findings suggested that the complex mode of inheritance that resulted in female mosquitoes showing a stronger tendency to return to their preferred host was obscured by the nature of the method of collection, i.e., wild parental females selecting a host either innately or opportunistically, the majority of which were likely innately attracted. This was revealed by F1 females, of which, when given the choice to select a host, a higher proportion opted for the preferred one. The results presented here are in accordance with other studies that identified a subpopulation of An. vestitipennis in southern Mexico with higher anthropophily.

Plasmodium berghei ookinetes induce nitric oxide production in Anopheles pseudopunctipennis midguts cultured in vitro

The Anopheles pseudopunctipennis nitric oxide synthase gene (ApNOS) was identified and its partial sequence showed high homology with NOS from A. stephensi, A. gambiae (putative sequence), and Drosophila melanogaster. ApNOS was mainly expressed in male and female adult mosquitoes and was induced by a blood meal. Nitric oxide (NO) was produced by in vitro-cultured mosquito midguts inoculated by enema with Plasmodium berghei ookinetes, Saccharomyces cerevisiae, Gram-positive bacteria (Micrococcus luteus), but not with Gram-negative bacteria (Klebsiella pneumoniae, Escherichia coli or Serratia marcescens). Dihydroxyphenylalanine (L-DOPA) oxidation induced the generation of NO in midguts in vitro, and hydrogen peroxide generated during its oxidation induced ApNOS expression. P. berghei ookinetes exposed in vitro to L-DOPA and sodium nitroprusside (a NO generator) were killed. These observations demonstrate that reactive oxygen and nitrogen intermediates constitute a part of the cytotoxic arsenal employed by Anopheles mosquitoes against microbial pathogens and Plasmodium ookinetes.

[Physico-chemical signals involved in host localization and in the induction of mosquito bites]

Disease vector female mosquitoes respond to physic-chemical signals to localize vertebrate hosts for blood meals. Zoophylic mosquitoes preferentially respond to CO2 and octenol released in the breath and bodily fluids, while anthropophylic mosquitoes respond to lactic acid and a variety of sweat compounds. These compounds are modified by saprophytic microorganisms in the skin sebaceous glands. Other factors present in human dwellings contribute to the integration of microsystems with characteristic odors that have different attraction for mosquitoes, explaining the focalization of malaria transmission in few households in endemic areas. The identification of the chemical attractants and their molecular receptors could be used to complement new methods to attract mosquitoes to traps during epidemiological surveys, to increase their contact with insecticides in control interventions, and for genetic manipulation to divert mosquito bites towards other animal populations. The English version of this paper is available at:http://www.insp.mx/salud/index.html.

Phormidium animalis (Cyanobacteria: Oscillatoriaceae) supports larval development of Anopheles albimanus

The capability of Phormidium animalis, a cyanobacterium commonly found in larval habitats of Anopheles albimanus in southern Mexico, to support larval development of this mosquito was investigated. First-stage larvae were reared under insectary conditions with P. animalis ad libitum and their development was compared with larvae fed with wheat germ. The time of pupation and adult mosquito size, assessed by wing length, were similar in both groups, but fewer adult mosquitoes were obtained from larvae fed with the cyanobacteria. Nevertheless, these observations indicate that P. animalis is ingested and assimilated by larval An. albimanus, making this cyanobacterium a good candidate for genetic engineering for the introduction of mosquitocidal toxins for malaria control in the region.

Cyanobacteria associated with Anopheles albimanus (Diptera: Culicidae) larval habitats in southern Mexico

Cyanobacteria associated with Anopheles albimanus Wiedemann larval habitats from southern Chiapas, Mexico, were isolated and identified from water samples and larval midguts using selective medium BG-11. Larval breeding sites were classified according to their hydrology and dominant vegetation. Cyanobacteria isolated in water samples were recorded and analyzed according to hydrological and vegetation habitat breeding types, and mosquito larval abundance. In total, 19 cyanobacteria species were isolated from water samples. Overall, the most frequently isolated cyanobacterial taxa were Phormidium sp., Oscillatoria sp., Aphanocapsa cf. littoralis, Lyngbya lutea, P. animalis, and Anabaena cf. spiroides. Cyanobacteria were especially abundant in estuaries, irrigation canals, river margins and mangrove lagoons, and more cyanobacteria were isolated from Brachiaria mutica, Ceratophyllum demersum, and Hymenachne amplexicaulis habitats. Cyanobacteria were found in habitats with low to high An. albimanus larval abundance, but Aphanocapsa cf. littoralis was associated with habitats of low larval abundance. No correlation was found between water chemistry parameters and the presence of cyanobacteria, however, water temperature (29.2-29.4 degrees C) and phosphate concentration (79.8-136.5 ppb) were associated with medium and high mosquito larvae abundance. In An. albimanus larval midguts, only six species of cyanobacteria were isolated, the majority being from the most abundant cyanobacteria in water samples.

[Geographical coverage of the Mexican Healthcare System and a spatial analysis of utilization of its General Hospitals in 1998]

OBJECTIVE

To describe the geographical coverage of the Mexican Healthcare System (MHS) services and to assess the utilization of its General Hospitals.

MATERIAL AND METHODS

A Geographic Information System (GIS) was used to include sociodemographic data by locality, the geographical location of all MHS healthcare services, and data on hospital discharge records. A maximum likelihood estimation model was developed to assess the utilization levels of 217 MHS General Hospitals. The model included data on human resources, additional infrastructure, and the population within a 25 km radius.

RESULTS

In 1998, 10,806 localities with 72 million inhabitants had at least one public healthcare unit, and 97.2% of the population lived within 50 km of a healthcare unit; however, over 18 million people lived in rural localities without a healthcare unit. The mean annual hospital occupation rate was 48.5 +/- 28.5 per 100 bed/years, with high variability within and between states. Hospital occupation was significantly associated with the number of physicians in the unit, and in the Mexican Institute of Social Security units utilization was associated with additional health infrastructure, and with the population's poverty index.

CONCLUSIONS

GIS analysis allows improved estimation of the coverage and utilization of MHS hospitals.

Pteridine concentrations differ between insectary-reared and field-collected Anopheles albimanus mosquitoes of the same physiological age

Biopterin, isoxanthopterin and 6-pterincarboxylic acid were identified in the head of the malaria vector mosquito Anopheles albimanus Weidemann (Diptera: Culicidae) by HPLC. Total pteridine concentrations (TPC) were estimated in heads, body parts (BP: abdomen, legs and wings) and whole bodies of insectary-reared and field-collected females, by spectrofluorometry, to investigate whether they could be used for age determination. Pteridine concentrations diminished with age in both mosquito groups. TPC correlated with chronological age in insectary-reared sugar-fed females (heads: r2 = 0.35, BP: r2 = 0.34, P < 0.001), but lower correlation occurred in blood-fed females (heads: r2 = 0.22, BP: r2 = 0.27). TPC differed among females of the same age fed with blood at different times (P < 0.05), indicating that bloodmeals modify the diminution rate of pteridines with age. Nevertheless, a polynomial significant correlation was documented for TPC and the number of ovipositions (heads: r2 = 0.24, BP: r2 = 0.27, whole body: r2 = 0.52, P < 0.001) in insectary-reared mosquitoes. This correlation was lower in field-collected mosquitoes (heads: r2 = 0.14, BP: r2 = 0.10, P < 0.05), which showed a remarkable pteridine increase in one-parous females. The correlation of TPC in whole body with physiological age was much less (r2 = 0.03). These observations indicate that TPC determination by spectrofluorometry is not a reliable method to estimate the age of An. albimanus females from the feral population.

Superoxide anion in Anopheles albimanus hemolymph and midgut is toxic to Plasmodium berghei ookinetes

The mechanisms of Plasmodium spp. elimination in resistant mosquitoes are not completely understood. Some resistant anopheline strains are able to melanize Plasmodium spp. ookinetes in their midguts. Because quinoid compounds are potent catalysts for free radical generation and because these radicals can be generated in association with melanogenesis, it is probable that they play an important role in the elimination of parasites. The production of the superoxide anion (O-2) in the hemolymph and midgut of Anopheles albimanus female mosquitoes and its cytotoxic effect on Plasmodium berghei ookinetes were analyzed. Ookinetes inoculated into the hemocoel of A. albimanus were covered with melanin and then encapsulated by hemocytes within 1 hr. The presence of O-2 in midguts and in hemolymph obtained by perfusion was verified by the reduction of 3-(4,5 dimethylthiazolil-2)-2,5-diphenyl tetrazolium bromide. O-2 was generated in the hemolymph obtained by perfusion and midguts only in the presence of dihydroxyphenylalanine (L-DOPA), and this reaction was inhibited by superoxide dismutase (SOD). Plasmodium berghei ookinetes exposed to hemolymph plus L-DOPA were killed in vitro, but addition of SOD prevented their killing. Prophenoloxidase transcripts were not observed in midgut epithelium, suggesting that toxic compounds may be imported from the hemolymph. These results suggest that A. albimanus hemolymph and midguts produce O-2 that may limit Plasmodium spp. parasite development.

From noxiustoxin to scorpine and possible transgenic mosquitoes resistant to malaria

Scorpion venom contains different types of peptides toxic to a variety of organisms whose molecular targets have been described as mainly ion-channels of excitable cells where they cause impairment of function. Based on mouse, cricket, and crustacean bioassays, specific toxins for each group of animals have been found. Chromatographic techniques were used to isolate and chemically characterize these peptides. One of the best-studied peptides is noxiustoxin, a 39-amino acid residue-long peptide specific for K(+)-channels. Hadrurin is another scorpion venom peptide whose activity was shown to be bactericidal to a variety of species. Structural similarities of a newly discovered peptide (scorpine) with those of defensins and cecropins showed that scorpion venom contains peptides toxic to microorganisms and malaria parasites. Scorpine was shown to disrupt the sporogonic development of Plasmodium berghei. Using this system as a model for malaria, we introduced the gene of scorpine into a vector for generation of transgenic flies resistant to the infection by Plasmodium. The final aim of this work is to incorporate this gene under the promoter of proteolytic enzymes of digestive tract of mosquitoes for synthesis and liberation of toxic peptide(s) into stomach of freshly fed mosquitoes potentially carrying Plasmodium gametes. In this manner, a putative transgenic mosquito with these characteristics would secrete a toxic peptide with digestive enzymes into midgut, impairing proper development of Plasmodium, hence controlling malaria, one of the most important tropical diseases worldwide.

Gender-related family head schooling and Aedes aegypti larval breeding risk in southern Mexico

OBJECTIVE

To investigate if family head genre-associated education is related to the risk of domiciliary Aedes aegypti larval breeding in a dengue-endemic village of Southern Mexico.

MATERIAL AND METHODS

A family head was considered to have a low education level if he/she had not completed elementary school. To estimate larval breeding risk within each household, a three-category Maya index was constructed using a weighted estimation of controllable and disposable domestic water containers. A socio-economic index was constructed based on household construction characteristics.

RESULTS

Low-level education of either family head was associated to higher larval breeding risk. Households with low-educated mothers had more larval breeding containers. These associations persisted after adjusting for household socio-economic level.

CONCLUSIONS

These results indicate that households with female family heads with low education levels accumulate more containers that favor Ae. aegypti breeding, and that education campaigns for dengue control should be addressed to this part of the population. The English version of this paper is available too at: http://www.insp.mx/salud/index.html.

Cellular-mediated reactions to foreign organisms inoculated into the hemocoel of Anopheles albimanus (Diptera: Culicidae)

The immune response against different organisms and particles inoculated in the hemocoel of female Anopheles albimanus Wiedemann was investigated. Histological and ultrastructural observations indicated that melanization and hemocyte type participation varied according to the particles inoculated. The initial responses against heat-killed Microccocus lysodeikticus and Escherichia coli included hemocyte lysis and melanization whereas the response to heat-killed Saccharomyces cerevisiae was only cellular, and an initial melanization of Sephadex G-25 (neutral charged) beads was followed by the formation of cellular aggregates. After 24 h, hemocytes were involved in all terminal encapsulation events. Plasmodium vivax Grassi and Feletti formalin-fixed sporozoites induced a weak response. Cellular aggregates were observed 1 h postinoculation, but participating hemocytes could not be identified because of the extensive cellular damage and lysis. Sporozoites were also observed in the core of these aggregates, mixed with cell debris and free in the hemolymph. The effect on the inoculated particles was also different-S. cerevisiae was encapsulated only by hemocytes, whereas M. lysodeikticus was lysed and E. coli was phagocytosed by plasmatocytes. These results indicate that hemocytes are important components in the immune response in An. albimanus.

Selective oviposition by Aedes aegypti (Diptera: culicidae) in response to Mesocyclops longisetus (Copepoda: Cyclopoidea) under laboratory and field conditions

The influence of predacious Mesocyclops longisetus Thiebaud on the selection of oviposition sites by prey Aedes aegypti (L.) was studied under laboratory and field conditions. In both cases, gravid Ae. aegypti females were significantly more attracted to ovitraps containing copepods or to ovitraps with water in which copepods were held previously than to distilled water. Monoterpene and sesquiterpene compounds including 3-carene, alpha-terpinene, alpha-copaene, alpha-longipinene, alpha-cedrene, and delta-cadinene were found in hexane extracts of copepods by gas chromatography and mass spectrometry analyses. These compounds may be responsible for attracting gravid Ae. aegypti females and may increase the number of potential prey for the copepod.

Scorpine, an anti-malaria and anti-bacterial agent purified from scorpion venom

A novel peptide, scorpine, was isolated from the venom of the scorpion Pandinus imperator, with anti-bacterial activity and a potent inhibitory effect on the ookinete (ED(50) 0.7 microM) and gamete (ED(50) 10 microM) stages of Plasmodium berghei development. It has 75 amino acids, three disulfide bridges with a molecular mass of 8350 Da. Scorpine has a unique amino acid sequence, similar only to some cecropins in its N-terminal segment and to some defensins in its C-terminal region. Its gene was cloned from a cDNA library.

Detection of Onchocerca volvulus infection in Simulium ochraceum sensu lato: comparison of a PCR assay and fly dissection in a Mexican hypoendemic community

Detection of Onchocerca volvulus larvae in vector populations is of prime importance in the assessment of the effectiveness of onchocerciasis control programmes. Traditionally, detection of larvae is attained by the dissection of flies, but this time-consuming method cannot easily discriminate between species of Onchocerca. The genome of all Onchocerca species has a unique 150 bp repeat, which can be amplified by PCR, and O. volvulus-specific DNA probes can detect these products by Southern blot (SB). This study optimizes a PCR/SB assay, and compares it with fly dissection to estimate the prevalence (p) and intensity of infection (m) in the local vector population of a Mexican community that has become hypoendemic as a result of 7 years of treatment with ivermectin and nodulectomy. The PCR detected 1 infected fly in a pool of 99 uninfected flies, but the optimal pool size was 50 flies. At the community level, 1 out of 10,550 flies was positive (p = 0.0095%, 95% confidence intervals CI = 0.00024-0.05280%; m = 0.00027 larvae/parous fly, CI = -0.00026-0.00081) by PCR, and 4 out of 10,772 flies (p = 0.0371%, CI = 0.01012-0.09505%; m = 0.00107 larvae/parous fly, 95% CI = 0.00002-0.00212) by dissection (observed m = 0.0005). Both methods produce statistically similar estimates of the prevalence and intensity, indicating that pool screening is a viable alternative for entomological surveillance in areas where the intensity of transmission is becoming extremely low as a result of control interventions.