Towards a unified curriculum system based on a public health holistic approach. Renovation of the academic programs at the School of Public Health of Mexico.

Public health training cannot be practiced in isolation, but rather within the framework of substantive conceptual visions, the organizational structure and teaching culture in a broad sense. The School of Public Health of Mexico (ESPM), in the mist of its 100th anniversary, is implementing an educational restructure with the guidance of conceptual and ethical principles. The restructure of the academic pro-grams will follow a constructivist pedagogical model, based on renewed institutional practices that integrates research, teaching and community outreach, making for truly transfor-mative learning. The new design of the whole structure of its academic programs has the objetive of making them flexible, less technical-based but more practical, and a within an uni-fied curricular system that articulates and allows continuity between master's degrees and doctorates programs. In the new structure, the curriculum will have a common core for all the academic programs, emerging from the study of the essential bases of public health, human rights, including gender and social perspectives, principles of global health, ethics of public health practice, environmental and animal health inferences and community outreach in the form of social retribution. The Institute's research groups will be the functional units for investigation and teaching, thus students will be integrated into these at an early stage, under the guidance of a tutor. In this context, the requirements for a comprehensive, unifying and at the same time flexible cur-riculum will support training of Public Health with a holistic approach. The current programs were analyzed including the review of their courses, regarding the pertinence of their contents and proposed competencies. We present herein a description of these observations, and propose a new com-mon core (conceptual-operative) with compulsory courses as the base for all programs. The participation of all academic bodies in reviewing the proposed new common core, as well as the syllabus and courses, identified those that are essential in each program's study concentration area, is indicated.

Development of the indirect flight muscles of Aedes aegypti, a main arbovirus vector.

BACKGROUND: Flying is an essential function for mosquitoes, required for mating and, in the case of females, to get a blood meal and consequently function as a vector. Flight depends on the action of the indirect flight muscles (IFMs), which power the wings beat. No description of the development of IFMs in mosquitoes, including Aedes aegypti, is available. METHODS: A. aegypti thoraces of larvae 3 and larvae 4 (L3 and L4) instars were analyzed using histochemistry and bright field microscopy. IFM primordia from L3 and L4 and IFMs from pupal and adult stages were dissected and processed to detect F-actin labelling with phalloidin-rhodamine or TRITC, or to immunodetection of myosin and tubulin using specific antibodies, these samples were analyzed by confocal microscopy. Other samples were studied using transmission electron microscopy. RESULTS: At L3-L4, IFM primordia for dorsal-longitudinal muscles (DLM) and dorsal-ventral muscles (DVM) were identified in the expected locations in the thoracic region: three primordia per hemithorax corresponding to DLM with anterior to posterior orientation were present. Other three primordia per hemithorax, corresponding to DVM, had lateral position and dorsal to ventral orientation. During L3 to L4 myoblast fusion led to syncytial myotubes formation, followed by myotendon junctions (MTJ) creation, myofibrils assembly and sarcomere maturation. The formation of Z-discs and M-line during sarcomere maturation was observed in pupal stage and, the structure reached in teneral insects a classical myosin thick, and actin thin filaments arranged in a hexagonal lattice structure. CONCLUSIONS: A general description of A. aegypti IFM development is presented, from the myoblast fusion at L3 to form myotubes, to sarcomere maturation at adult stage. Several differences during IFM development were observed between A. aegypti (Nematoceran) and Drosophila melanogaster (Brachyceran) and, similitudes with Chironomus sp. were observed as this insect is a Nematoceran, which is taxonomically closer to A. aegypti and share the same number of larval stages.

Vertical transmission of dengue virus in Aedes aegypti and its role in the epidemiological persistence of dengue in Central and Southern Mexico.

BACKGROUND: Aedes aegypti and Aedes albopictus are the main mosquito species responsible for dengue virus (DENV) transmission to humans in the tropical and subtropical regions of the world. The role of vertical transmission in the epidemiology of dengue and the maintenance of this arbovirus in nature during interepidemic periods remain poorly understood, and DENV vertical transmission could sustain the existence of virus reservoirs within Aedes populations. METHODS: Between April 2011 and October 2012, we monitored vertical transmission of DENV in Ae. aegypti and Ae. albopictus in 9 cities of 4 Mexican states. Aedes eggs were collected in ovitraps, then adults were reared under laboratory conditions and their heads were used to infect C6/36 cells. The presence of flavivirus was detected by immunofluorescence assays (IFA), and DENV infection was confirmed by RT-PCR. RESULTS: About 96% of reared adults were Ae. aegypti and 4.0% were Ae. albopictus. No infection was detected in Ae. albopictus, whereas 54 of 713 (7.8%) of Ae. aegypti pools tested positive. A minimum infection rate (MIR) of 2.52 per 1000 mosquitoes was estimated for Ae. aegypti. DENV-1, DENV-2 & DENV-3 serotypes were detected even during interepidemic periods. CONCLUSIONS: This study reports the evidence of vertical transmission of dengue virus with viral isolation and molecular confirmation in Ae. aegypti eggs collected in four endemic regions of Central and Southern Mexico. Vertical transmission may play a role as a reservoir mechanism during mosquito dormancy in interepidemic periods but with minor participation in transmission during epidemic periods.

TRANSMISSION VERTICALE DU VIRUS DE LA DENGUE CHEZ AEDES AEGYPTI ET SON RÔLE DANS LA PERSISTANCE ÉPIDÉMIOLOGIQUE DE LA DENGUE DANS LE CENTRE ET LE SUD DU MEXIQUE: OBJECTIF: Aedes aegypti et Aedes albopictus sont les principales espèces de moustiques responsables de la transmission du virus de la dengue (DENV) à l'homme dans les régions tropicales et subtropicales du monde. Le rôle de la transmission verticale dans l'épidémiologie de la dengue et le maintien de cet arbovirus dans la nature pendant les périodes d'inter-épidémiques restent mal compris, et la transmission verticale du DENV pourrait maintenir l'existence de réservoirs de virus au sein des populations d'Aedes. Notre objectif était d'évaluer la transmission verticale du DENV au Mexique. MÉTHODES: Entre avril 2011 et octobre 2012, nous avons surveillé la transmission verticale du DENV chez Ae. aegypti et Ae. albopictus dans 9 villes de 4 états mexicains. Les œufs d'Aedes ont été collectés dans des ovitraps, puis les adultes ont été élevés dans des conditions de laboratoire et leur tête a été utilisée pour infecter les cellules C6/36. La présence de flavivirus a été détectée par des tests d'immunofluorescence (IFA) et l'infection par DENV a été confirmée par RT-PCR. RÉSULTATS: 96% des adultes élevés étaient Ae. aegypti et 4,0% étaient Ae. albopictus. Aucune infection n'a été détectée chez Ae. albopictus, alors que 54 des 713 (7,8%) des pools d'Ae. aegypti ont été testés positifs. Un taux d'infection minimum (MIR) de 2,52 pour 1000 moustiques a été estimé pour Ae. aegypti. Les sérotypes DENV-1, DENV-2 et DENV-3 ont été détectés même pendant les périodes inter-épidémiques. CONCLUSIONS: Cette étude rapporte les preuves de transmission verticale du virus de la dengue avec isolement viral et confirmation moléculaire dans les œufs d'Ae. Aegypti collectés dans quatre régions d'endémie du centre et du sud du Mexique. La transmission verticale pourrait jouer un rôle de mécanisme réservoir lors de la dormance des moustiques en période inter-épidémique, mais avec une participation mineure à la transmission en période d'épidémie.

Adaptations in energy metabolism and gene family expansions revealed by comparative transcriptomics of three Chagas disease triatomine vectors.

BACKGROUND: Chagas disease is a parasitic infection caused by Trypanosoma cruzi. It is an important public health problem affecting around seven to eight million people in the Americas. A large number of hematophagous triatomine insect species, occupying diverse natural and human-modified ecological niches transmit this disease. Triatomines are long-living hemipterans that have evolved to explode different habitats to associate with their vertebrate hosts. Understanding the molecular basis of the extreme physiological conditions including starvation tolerance and longevity could provide insights for developing novel control strategies. We describe the normalized cDNA, full body transcriptome analysis of three main vectors in North, Central and South America, Triatoma pallidipennis, T. dimidiata and T. infestans. RESULTS: Two-thirds of the de novo assembled transcriptomes map to the Rhodnius prolixus genome and proteome. A Triatoma expansion of the calycin family and two types of protease inhibitors, pacifastins and cystatins were identified. A high number of transcriptionally active class I transposable elements was documented in T. infestans, compared with T. dimidiata and T. pallidipennis. Sequence identity in Triatoma-R. prolixus 1:1 orthologs revealed high sequence divergence in four enzymes participating in gluconeogenesis, glycogen synthesis and the pentose phosphate pathway, indicating high evolutionary rates of these genes. Also, molecular evidence suggesting positive selection was found for several genes of the oxidative phosphorylation I, III and V complexes. CONCLUSIONS: Protease inhibitors and calycin-coding gene expansions provide insights into rapidly evolving processes of protease regulation and haematophagy. Higher evolutionary rates in enzymes that exert metabolic flux control towards anabolism and evidence for positive selection in oxidative phosphorylation complexes might represent genetic adaptations, possibly related to prolonged starvation, oxidative stress tolerance, longevity, and hematophagy and flight reduction. Overall, this work generated novel hypothesis related to biological adaptations to extreme physiological conditions and diverse ecological niches that sustain Chagas disease transmission.

Pathogen-insect interaction candidate molecules for transmission-blocking control strategies of vector borne diseases.

OBJECTIVE: To analyze the current knowledge of pathogen-insect interactions amenable for the design of molecular-based control strategies of vector-borne diseases. MATERIALS AND METHODS: We examined malaria, dengue, and Chagas disease pathogens and insect molecules that participate in interactions during their vectors infection. RESULTS: Pathogen molecules that participate in the insect intestine invasion and induced vector immune molecules are presented, and their inclusion in transmission blocking vaccines (TBV) and in genetically modify insect (GMI) vectors or symbiotic bacteria are discussed. CONCLUSIONS: Disruption of processes by blocking vector-pathogen interactions provides several candidates for molecular control strategies, but TBV and GMI efficacies are still limited and other secondary effects of GMI (improving transmission of other pathogens, affectation of other organisms) should be discarded.

Association of dengue fever with Aedes spp. abundance and climatological effects.

OBJECTIVE: To analyze the association of dengue fever incidence with Aedes mosquito's abundance, and the effect of climatological and geographical variables, in a region in Morelos State, Mexico. MATERIALS AND METHODS: Weekly data during the period 2010 to 2014 was used. Mosquito abundance was determined using ovitraps. Confirmed dengue cases were obtained from the Epidemiological Surveillance System. Climatic variables were obtained from weather monitoringstations. The correlation between climate variables and ovitraps data was estimated using a multivariate regression model. RESULTS: A correlation of mosquito abundance with dengue fever incidence, and a yearly pattern with seasonal variations were observed. The daily mean temperature, relative humidity and rainfall parameters were associated with mosquito egg abundance. Time lags of three and four weeks between egg counts and dengue fever incidence were observed. CONCLUSION: Time lags between egg counts and dengue incidence could be useful for prevention and control interventions.

Ecdysis-related pleiotropic neuropeptides expression during Anopheles albimanus development.

OBJECTIVE: To analyze the transcription pattern of neuropeptides in the ontogeny of a malaria vector, the mosquito Anopheles albimanus. MATERIALS AND METHODS: The transcription pattern of Crustacean CardioActive peptide (CCAP), corazonin, Ecdysis Triggering Hormone (ETH), allatostatin-A, orcokinin, Insulin Like Peptide 2 (ILP2), Insulin Like Peptide 5 (ILP5) and bursicon was evaluated using qPCR on larvae (1st - 4th instar), pupae and adult mosquitoes. RESULTS: Unlike in other insects, transcripts of CCAP (70.8%), ETH (60.2%) and corazonin (76.5%) were expressed in 4th instar larvae, probably because these three neuropeptides are associated with the beginning of ecdysis. The neuropeptide ILP2 showed higher transcription levels in other stages and orcokinin decreased during the development of the mosquito. CONCLUSIONS: The CCAP, corazonin and ETH neuropeptidesare potential targets for the design of control strategies aimed at disrupting An. albiamnus larval development.

Design and efficacy of an Ecohealth competency-based course on the prevention and control of vector diseases in Latin America.

OBJECTIVE: To design and analyze the efficacy of an Ecohealth competency-based course on the prevention and control of vector-borne-diseases for specific stakeholders. MATERIALS AND METHODS: Multiple stakeholders and sectors of the region were consulted to identify Ecohealth group-specific competencies using an adjusted analysis matrix. Eight courses based on the competencies were implemented to train EA tutors. The effectiveness of the course was evaluated through the use of paired- t-tests by intervention group. RESULTS: Strategic, tactical, academia and community stakeholder groups and their competencies were identified. An overall gain of 43 percentage points (p<0.001) was observed in terms of competencies score in trained tutors, which further trained 1 033 people. CONCLUSIONS: The identification of the stakeholders and their competencies proved to be useful to guide training courses to significantly improve the initial competencies and create a critical mass to further advance the EA in the region.

Cellular stress associated with the differentiation of Plasmodium berghei ookinetes.

For malaria transmission, Plasmodium parasites must develop in the mosquito vector. Oxidative stress in the insect midgut, triggered by environmental changes (e.g., pH and temperature), influences the cellular signaling involved in differentiation from gametocytes to mobile ookinetes for the purpose of parasite survival. Oxidative stress activates the homeostatic response to stress characterized by the phosphorylation eIF2α, the attenuation of protein synthesis, and the transcription of genes participating in the unfolded protein response and antioxidant processes, forming a part of an integrated stress response (ISR). We hypothesized that ISR operates during the differentiation of gametocytes to ookinetes to assure Plasmodium survival. Using in-vitro conditions resembling the mosquito midgut conditions, we cultured Plasmodium berghei gametocytes to ookinetes and evaluated the redox balance by detecting reactive oxygen species and superoxide dismutase activity. Additionally, we evaluated the phosphorylation of eIF2α, the attenuation of the global protein synthesis, and the gene expression of cellular stress markers (e.g., endoplasmic reticulum chaperones and antioxidant molecules, measured by reverse-transcription quantitative polymerase chain reaction), finding that these processes were all taking place, probably to improve survival during the differentiation of Plasmodium berghei ookinetes.

A bioinformatics approach for integrated transcriptomic and proteomic comparative analyses of model and non-sequenced anopheline vectors of human malaria parasites.

Malaria morbidity and mortality caused by both Plasmodium falciparum and Plasmodium vivax extend well beyond the African continent, and although P. vivax causes between 80 and 300 million severe cases each year, vivax transmission remains poorly understood. Plasmodium parasites are transmitted by Anopheles mosquitoes, and the critical site of interaction between parasite and host is at the mosquito's luminal midgut brush border. Although the genome of the "model" African P. falciparum vector, Anopheles gambiae, has been sequenced, evolutionary divergence limits its utility as a reference across anophelines, especially non-sequenced P. vivax vectors such as Anopheles albimanus. Clearly, technologies and platforms that bridge this substantial scientific gap are required in order to provide public health scientists with key transcriptomic and proteomic information that could spur the development of novel interventions to combat this disease. To our knowledge, no approaches have been published that address this issue. To bolster our understanding of P. vivax-An. albimanus midgut interactions, we developed an integrated bioinformatic-hybrid RNA-Seq-LC-MS/MS approach involving An. albimanus transcriptome (15,764 contigs) and luminal midgut subproteome (9,445 proteins) assembly, which, when used with our custom Diptera protein database (685,078 sequences), facilitated a comparative proteomic analysis of the midgut brush borders of two important malaria vectors, An. gambiae and An. albimanus.

Protein phosphorylation during Plasmodium berghei gametogenesis.

Plasmodium gametogenesis within the mosquito midgut is a complex differentiation process involving signaling mediated by phosphorylation, which modulate metabolic routes and protein synthesis required to complete this development. However, the mechanisms leading to gametogenesis activation are poorly understood. We analyzed protein phosphorylation during Plasmodium berghei gametogenesis in vitro in serum-free medium using bidimensional electrophoresis (2-DE) combined with immunoblotting (IB) and antibodies specific to phosphorylated serine, threonine and tyrosine. Approximately 75 protein exhibited phosphorylation changes, of which 23 were identified by mass spectrometry. These included components of the cytoskeleton, heat shock proteins, and proteins involved in DNA synthesis and signaling pathways among others. Novel phosphorylation events support a role for these proteins during gametogenesis. The phosphorylation sites of six of the identified proteins, HSP70, WD40 repeat protein msi1, enolase, actin-1 and two isoforms of large subunit of ribonucleoside reductase were investigated using TiO2 phosphopeptides enrichment and tandem mass spectrometry. In addition, transient exposure to hydroxyurea, an inhibitor of ribonucleoside reductase, impaired male gametocytes exflagellation in a dose-dependent manner, and provides a resource for functional studies.

[Malaria's seroepidemiology in a group of migrants in transit (Chiapas, 2008)]. / Seroepidemiología del paludismo en un grupo de migrantes en tránsito (Chiapas, 2008).

OBJECTIVE: To know the prevalence of malaria and the factors associated with the infection in migrants in the southern border of Mexico, during 2008. MATERIALS AND METHODS: In 706 migrants, active malaria infection was investigated using a rapid diagnostic test and PCR and past infection using serology. A questionnaire was applied to investigate the conditions associated to infection. RESULTS: 85.6% originated from Central America, none presented an active infection, although 4.2% were seropositive, most of these came from the countries with the highest malaria incidence in the region. Seropositivity was associated with the number of previous malaria episodes (OR=1.44; IC95% 1.04-2.00), years living in their community of origin (OR=1.03; IC95% 1.00-1.07), and knowledge and self-medication with anti-malaria drugs (OR=3.38; IC95% 1.48-7.67). CONCLUSIONS: . The previous exposure of migrants and the difficulties for their detection indicate the need of new strategies for the epidemiological surveillance for these populations.

A research agenda to underpin malaria eradication.

The interruption of malaria transmission worldwide is one of the greatest challenges for international health and development communities. The current expert view suggests that, by aggressively scaling up control with currently available tools and strategies, much greater gains could be achieved against malaria, including elimination from a number of countries and regions; however, even with maximal effort we will fall short of global eradication. The Malaria Eradication Research Agenda (malERA) complements the current research agenda--primarily directed towards reducing morbidity and mortality--with one that aims to identify key knowledge gaps and define the strategies and tools that will result in reducing the basic reproduction rate to less than 1, with the ultimate aim of eradication of the parasite from the human population. Sustained commitment from local communities, civil society, policy leaders, and the scientific community, together with a massive effort to build a strong base of researchers from the endemic areas will be critical factors in the success of this new agenda.

Shrinking the malaria map: progress and prospects.

In the past 150 years, roughly half of the countries in the world eliminated malaria. Nowadays, there are 99 endemic countries-67 are controlling malaria and 32 are pursuing an elimination strategy. This four-part Series presents evidence about the technical, operational, and financial dimensions of malaria elimination. The first paper in this Series reviews definitions of elimination and the state that precedes it: controlled low-endemic malaria. Feasibility assessments are described as a crucial step for a country transitioning from controlled low-endemic malaria to elimination. Characteristics of the 32 malaria-eliminating countries are presented, and contrasted with countries that pursued elimination in the past. Challenges and risks of elimination are presented, including Plasmodium vivax, resistance in the parasite and mosquito populations, and potential resurgence if investment and vigilance decrease. The benefits of elimination are outlined, specifically elimination as a regional and global public good. Priorities for the next decade are described.

Operational strategies to achieve and maintain malaria elimination.

Present elimination strategies are based on recommendations derived during the Global Malaria Eradication Program of the 1960s. However, many countries considering elimination nowadays have high intrinsic transmission potential and, without the support of a regional campaign, have to deal with the constant threat of imported cases of the disease, emphasising the need to revisit the strategies on which contemporary elimination programmes are based. To eliminate malaria, programmes need to concentrate on identification and elimination of foci of infections through both passive and active methods of case detection. This approach needs appropriate treatment of both clinical cases and asymptomatic infections, combined with targeted vector control. Draining of infectious pools entirely will not be sufficient since they could be replenished by imported malaria. Elimination will thus additionally need identification and treatment of incoming infections before they lead to transmission, or, more realistically, embarking on regional initiatives to dry up importation at its source.

[Plan to improve malaria control towards its elimination in Mesoamerica]. / Plan de mejoramiento del control de la malaria hacia su eliminación en Mesoamérica.

To develop a plan to strengthen the control of malaria towards its elimination. In 2009, under the coordination of the National Public HealthInstitute ofMexico, atransdisciplinary equipment of technical and operative experts was conformed to carry out a situational analysis of malaria and control programs and for the selection of effective practices of intervention that would be incorporated to the plan, within the framework of an exercise in Theory of Change. Criteria for thestratificationof thelocalities, based ontheirtransmission characteristics were established. The structural and operative limitations of the control programs were identified. A plan of interventions was elaborated to improve the coverage of epidemiological surveillance, anti-malaria interventions and opportune diagnosis and treatment of cases. The plan delineates progressive phases of implementation: reorganization, intensification of interventions and evaluation of elimination feasibility. The adoption of a regional strategic plan will provide guidance and administrative elements to conform a system that coordinates the activities of the national control programs and facilitate the elimination of malaria in the region.

Effect of nitric oxide on Dengue virus replication in Aedes aegypti and Anopheles albimanus.

UNLABELLED: Dengue virus (DENV) is transmitted to humans by Aedes sp. mosquitoes. Little is known about the cellular and molecular interactions between the virus and the mosquito. The identification of resistance mechanisms could provide insight for the development of control strategies based on genetic manipulation. OBJECTIVE: To determine the effect of nitric oxide (NO) donors/inhibitors on DENV replication in Aedes aegypti and Anopheles albimanus. MATERIALS AND METHODS: Ae. aegypti and An. albimanus were fed with a blood suspension supplemented with DENV and donors/inhibitors of NO; DENV replication was assessed by immunofluorescence, RT-PCR and qRT-PCR parallel to NO measurement by means of the Griess reaction. RESULTS: DENV replicates at 3x10(6) genome copies/day/mosquito in Aedes. In comparison, no evidence of virus genome accumulation was detected when 2 mM sodium nitroprusside, a NO donor, were added to the infected blood meal. DENV did not replicate in Anopheles unless 1 mM L-N(G)-nitroarginine methyl ester, a NO synthesis inhibitor, was added to the infected blood meal, although the absolute viral load was significantly lower than in Aedes. CONCLUSIONS: As in humans, NO participates in the control of the virus load in mosquitoes. However, other mechanisms could also be involved in virus resistance in Anopheles.

Comparative genomics analysis of triatomines reveals common first line and inducible immunity-related genes and the absence of Imd canonical components among hemimetabolous arthropods.

BACKGROUND: Insects operate complex humoral and cellular immune strategies to fend against invading microorganisms. The majority of these have been characterized in Drosophila and other dipterans. Information on hemipterans, including Triatominae vectors of Chagas disease remains incomplete and fractionated. RESULTS: We identified putative immune-related homologs of three Triatominae vectors of Chagas disease, Triatoma pallidipennis, T. dimidiata and T. infestans (TTTs), using comparative transcriptomics based on established immune response gene references, in conjunction with the predicted proteomes of Rhodnius prolixus, Cimex lecticularis and Acyrthosiphon pisum hemimetabolous. We present a compressive description of the humoral and cellular innate immune components of these TTTs and extend the immune information of other related hemipterans. Key homologs of the constitutive and induced immunity genes were identified in all the studied hemipterans. CONCLUSIONS: Our results in the TTTs extend previous observations in other hemipterans lacking several components of the Imd signaling pathway. Comparison with other hexapods, using published data, revealed that the absence of various Imd canonical components is common in several hemimetabolous species.

The surface protein Pvs25 of Plasmodium vivax ookinetes interacts with calreticulin on the midgut apical surface of the malaria vector Anopheles albimanus.

Malaria parasite transmission-blocking control strategies within the mosquito vector require an adequate understanding of the parasite mosquito interaction at the molecular level. The ookinete P25-P28 surface proteins are required for the transition from ookinete to oocyst in the mosquito midgut; however, their respective molecular interactions in the mosquito are largely unknown. We used recombinant Pvs25 and Pvs28 as probes for identification of potential Anopheles albimanus midgut ligands. A 50 kDa protein interacted with Pvs25 but not with Pvs28 in blot overlay assays. This protein was identified as calreticulin by LS MS and was detected in membrane, but not in soluble midgut protein extracts. Calreticulin was detected in An. albimanus midgut microvilli by immunofluorescence analysis. The An. albimanus calreticulin cDNA was cloned and recombinant calreticulin was shown to interact with recombinant Pvs25 in overlay and co-immunoprecipitation assays, confirming the interaction of the two proteins. The Pvs25-calreticulin interaction in vivo could represent a potential target for developing transmission blocking strategies based on interfering the parasite-midgut interaction.