Two Novel Mosquitocidal Peptides Isolated from the Venom of the Bahia Scarlet Tarantula (Lasiodora klugi).

Effective control of diseases transmitted by Aedes aegypti is primarily achieved through vector control by chemical insecticides. However, the emergence of insecticide resistance in A. aegypti undermines current control efforts. Arachnid venoms are rich in toxins with activity against dipteran insects and we therefore employed a panel of 41 spider and 9 scorpion venoms to screen for mosquitocidal toxins. Using an assay-guided fractionation approach, we isolated two peptides from the venom of the tarantula Lasiodora klugi with activity against adult A. aegypti. The isolated peptides were named U-TRTX-Lk1a and U-TRTX-Lk2a and comprised 41 and 49 residues with monoisotopic masses of 4687.02 Da and 5718.88 Da, respectively. U-TRTX-Lk1a exhibited an LD50 of 38.3 pmol/g when injected into A. aegypti and its modeled structure conformed to the inhibitor cystine knot motif. U-TRTX-Lk2a has an LD50 of 45.4 pmol/g against adult A. aegypti and its predicted structure conforms to the disulfide-directed ß-hairpin motif. These spider-venom peptides represent potential leads for the development of novel control agents for A. aegypti.

Cross Talk between Viruses and Insect Cells Cytoskeleton.

Viruses are excellent manipulators of host cellular machinery, behavior, and life cycle, with the host cell cytoskeleton being a primordial viral target. Viruses infecting insects generally enter host cells through clathrin-mediated endocytosis or membrane fusion mechanisms followed by transport of the viral particles to the corresponding replication sites. After viral replication, the viral progeny egresses toward adjacent cells and reaches the different target tissues. Throughout all these steps, actin and tubulin re-arrangements are driven by viruses. The mechanisms used by viruses to manipulate the insect host cytoskeleton are well documented in the case of alphabaculoviruses infecting Lepidoptera hosts and plant viruses infecting Hemiptera vectors, but they are not well studied in case of other insect-virus systems such as arboviruses-mosquito vectors. Here, we summarize the available knowledge on how viruses manipulate the insect host cell cytoskeleton, and we emphasize the primordial role of cytoskeleton components in insect virus motility and the need to expand the study of this interaction.

Human blood microRNA hsa-miR-21-5p induces vitellogenin in the mosquito Aedes aegypti.

Mosquito vectors transmit various diseases through blood feeding, required for their egg development. Hence, blood feeding is a major physiological event in their life cycle, during which hundreds of genes are tightly regulated. Blood is a rich source of proteins for mosquitoes, but also contains many other molecules including microRNAs (miRNAs). Here, we found that human blood miRNAs are transported abundantly into the fat body tissue of Aedes aegypti, a key metabolic center in post-blood feeding reproductive events, where they target and regulate mosquito genes. Using an artificial diet spiked with the mimic of an abundant and stable human blood miRNA, hsa-miR-21-5p, and proteomics analysis, we found over 40 proteins showing differential expression in female Ae. aegypti mosquitoes after feeding. Of interest, we found that the miRNA positively regulates the vitellogenin gene, coding for a yolk protein produced in the mosquito fat body and then transported to the ovaries as a protein source for egg production. Inhibition of hsa-miR-21-5p followed by human blood feeding led to a statistically insignificant reduction in progeny production. The results provide another example of the involvement of small regulatory molecules in the interaction of taxonomically vastly different taxa.

The major oligosaccharyl transferase complex genes are not involved in dengue virus replication in Aedes aegypti mosquitoes.

Replication of the dengue virus (DENV) genome occurs in a vesicle in the endoplasmic reticulum by a complex of host and viral proteins. Two host proteins, STT3A and STT3B, as members of the oligosaccharyl transferase complex, have been implicated in playing structural roles in the vesicle in mammalian cells, and the absence of these proteins has been shown to decrease DENV replication. Aedes aegypti is the main vector of the virus and has been used previously as a model organism to study mosquito-virus interactions. In this study, we found that genes of the oligosaccharyl transferase complex have no effect on replication of DENV in mosquito cells.

Tyrosine Detoxification Is an Essential Trait in the Life History of Blood-Feeding Arthropods.

Blood-feeding arthropods are vectors of infectious diseases such as dengue, Zika, Chagas disease, and malaria [1], and vector control is essential to limiting disease spread. Because these arthropods ingest very large amounts of blood, a protein-rich meal, huge amounts of amino acids are produced during digestion. Previous work on Rhodnius prolixus, a vector of Chagas disease, showed that, among all amino acids, only tyrosine degradation enzymes were overexpressed in the midgut compared to other tissues [2]. Here we demonstrate that tyrosine detoxification is an essential trait in the life history of blood-sucking arthropods. We found that silencing Rhodnius tyrosine aminotransferase (TAT) and 4-hydroxyphenylpyruvate dioxygenase (HPPD), the first two enzymes of the phenylalanine/tyrosine degradation pathway, caused the death of insects after a blood meal. This was confirmed by using the HPPD inhibitor mesotrione, which selectively killed hematophagous arthropods but did not affect non-hematophagous insects. In addition, mosquitoes and kissing bugs died after feeding on mice that had previously received a therapeutic effective oral dose (1 mg/kg) of nitisinone, another HPPD inhibitor used in humans for the treatment of tyrosinemia type I [3]. These findings indicate that HPPD (and TAT) can be a target for the selective control of blood-sucking disease vector populations. Because HPPD inhibitors are extensively used as herbicides and in medicine, these compounds may provide an alternative less toxic to humans and more environmentally friendly than the conventional neurotoxic insecticides that are currently used, with the ability to affect only hematophagous arthropods.

Identification of a selenium-dependent glutathione peroxidase in the blood-sucking insect Rhodnius prolixus.

The selenium-dependent glutathione peroxidase (SeGPx) is a well-studied enzyme that detoxifies organic and hydrogen peroxides and provides cells or extracellular fluids with a key antioxidant function. The presence of a SeGPx has not been unequivocally demonstrated in insects. In the present work, we identified the gene and studied the function of a Rhodnius prolixus SeGPx (RpSeGPx). The RpSeGPx mRNA presents the UGA codon that encodes the active site selenocysteine (Sec) and a corresponding Sec insertion sequence (SECIS) in the 3' UTR region. The encoded protein includes a signal peptide, which is consistent with the high levels of GPx enzymatic activity in the insect's hemolymph, and clusters phylogenetically with the extracellular mammalian GPx03. This result contrasts with all other known insect GPxs, which use a cysteine residue instead of Sec and cluster with the mammalian phospholipid hydroperoxide GPx04. RpSeGPx is widely expressed in insect organs, with higher expression levels in the fat body. RNA interference (RNAi) was used to reduce RpSeGPx gene expression and GPx activity in the hemolymph. Adult females were apparently unaffected by RpSeGPx RNAi, whereas first instar nymphs showed a three-day delay in ecdysis. Silencing of RpSeGPx did not alter the gene expression of the antioxidant enzymes catalase, xanthine dehydrogenase and a cysteine-GPx, but it reduced the levels of the dual oxidase and NADPH oxidase 5 transcripts that encode for enzymes releasing extracellular hydrogen peroxide/superoxide. Collectively, our data suggest that RpSeGPx functions in the regulation of extracellular (hemolymph) redox homeostasis of R. prolixus.

Development of a community-based intervention for the control of Chagas disease based on peridomestic animal management: an eco-bio-social perspective.

BACKGROUND: Integrated vector management strategies depend on local eco-bio-social conditions, community participation, political will and inter-sectorial partnership. Previously identified risk factors for persistent Triatoma dimidiata infestation include the presence of rodents and chickens, tiled roofs, dirt floors, partial wall plastering and dog density. METHODS: A community-based intervention was developed and implemented based on cyclical stakeholder and situational analyses. Intervention implementation and evaluation combined participatory action research and cluster randomized pre-test post-test experimental designs. The intervention included modified insecticide application, education regarding Chagas disease and risk factors, and participatory rodent control. RESULTS: At final evaluation there was no significant difference in post-test triatomine infestation between intervention and control, keeping pre-test rodent and triatomine infestations constant. Knowledge levels regarding Chagas disease and prevention practices including rodent control, chicken management and health service access increased significantly only in intervention communities. The odds of nymph infection and rat infestation were 8.3 and 1.9-fold higher in control compared to intervention communities, respectively. CONCLUSION: Vector control measures without reservoir control are insufficient to reduce transmission risk in areas with persistent triatomine infestation. This integrated vector management program can complement house improvement initiatives by prioritizing households with risk factors such as tiled roofs. Requirement for active participation and multi-sectorial coordination poses implementation challenges.