[The genetics of insect disease vectors. Who program].
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Genetics, Population↗
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Cryptic species of insect disease vectors and their importance.
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Animals↗
Dynamic genome organization and gene evolution by positive selection in geminivirus (Geminiviridae).
Geminiviruses (Geminiviridae) are a diverse group of plant viruses differing from other known plant viruses in possessing circular, single-stranded DNA. Current classification divides the family into three subgroups, defined in part by genome organization, insect vector, and plant host range. Previous phylogenetic assessments of geminiviruses have used DNA and/or amino acid sequences from the replication-associated and coat protein genes and have relied predominantly on distance analyses. We used amino acid and DNA sequence data from the replication-associated and coat protein genes from 22 geminivirus types in distance and parsimony analyses. Although the results of our analyses largely agree with those reported previously, we could not always predict viral relationships based on genome organization, plant host, or insect vector. Loss of correlation of these traits with phylogeny is likely due to improved sampling of geminivirus types. Unrooted parsimony trees suggest multiple independent origins for the monopartite genome. genome organization is therefore a dynamic character. Estimates of nonsynonymous and synonymous nucleotide substitutions for extant and inferred ancestral sequences were used to evaluate hypotheses that the replication-associated and coat protein sequences evolve to accommodate plant host and insect vector specificities, respectively. Results suggest that plant host specificity does not solely direct replication-associated protein-evolution but that coat protein sequence does evolve in response to insect vector specificity. Genome organization and, possibly, plant host specificity are not reliable taxonomic characters.
Animals↗
A functional analysis of the P-element gene-transfer vector in insects.
A P-element mobility excision assay was used to determine if non-drosophilid insects could support P gene vector function. Present studies included the testing of Muscids, Sphaerocerids, and Phorids, none of which were able to support P mobility. A new excision indicator plasmid was developed allowing the detection and recovery of virtually all P-element excision products. The frequency and sequence analysis of excision products from Drosophila melanogaster and another drosophilid, Chymomyza procnemis, indicated both quantitative and qualitative differences in the activity of transposase. The quantitative relationships observed in the original assay were maintained, and qualitative differences in transposase activity were reflected in the sequence of the empty donor sites. The results suggest that host factors are involved in cutting and ligating P-element DNA during excision, with transposase facilitating these processes. Possible limitations on P mobility by abnormal transposase transcript processing were tested in Anastrepha suspensa using transposase-encoding plasmids having deleted intron sequences. A transposase cDNA supported normal P excision in D. melanogaster, and a low level of mobility in A. suspensa. Possible applications of gene transfer in insects are presented, in particular methods to genetically sterilize and sex insects for the sterile-insect technique.
Animals↗
Production of adeno-associated viral vectors in insect cells using triple infection: optimization of baculovirus concentration ratios.
The production of viral vectors or virus-like particles for gene therapy or vaccinations using the baculovirus expression system is gaining in popularity. Recently, reports of a viral vector based on adeno-associated virus (AAV) produced in insect cells using the baculovirus expression vector system have been published. This system requires the triple infection of cells with baculovirus vectors containing the AAV gene for replication proteins (BacRep), the AAV gene for structural proteins (BacCap), and the AAV vector genome (BacITR). A statistical approach was used to investigate the multiplicities of infection of the three baculoviruses and the results were extended to the production of AAVs containing various transgenes. Highest AAV yields were obtained when BacRep and BacCap, the baculovirus vectors containing genes that code for proteins necessary for the formation of the AAV vector, were added in equal amounts at high multiplicities of infection. These combinations also resulted in the closest ratios of infectious to total AAV particles produced. Overexpression of the AAV structural proteins led to the production of empty AAV capsids, which is believed to overload the cellular machinery, preventing proper encapsidation of the AAV vector transgene, and decreased the viability of the insect cells. Delaying the input of BacCap, to reduce the amount of capsids produced, resulted in lower infectious AAV titers then when all three baculoviruses were put into the system at the same time. The amount of BacITR added to the system can be less than the other two without loss of AAV yield.
Animals↗
Leishmaniasis and malaria: new tools for epidemiologic analysis.
Parasitic diseases are still prevalent in many parts of the world, causing both human suffering and economic loss. Recent developments in biotechnology, such as the use of monoclonal antibodies and recombinant DNA, have the potential for providing both more extensive and detailed information on the parasite in the infected human and in insect vectors. New methods of detection, both in man and insect vectors, have been developed for two parasitic diseases, leishmaniasis and malaria. These new methodologies will be important in epidemiologic studies on the prevalence and transmission of these parasitic diseases.
Antibodies, Monoclonal↗
A single amino acid position in the helper component of cauliflower mosaic virus can change the spectrum of transmitting vector species.
Viruses frequently use insect vectors to effect rapid spread through host populations. In plant viruses, vector transmission is the major mode of transmission, used by nearly 80% of species described to date. Despite the importance of this phenomenon in epidemiology, the specificity of the virus-vector relationship is poorly understood at both the molecular and the evolutionary level, and very limited data are available on the precise viral protein motifs that control specificity. Here, using the aphid-transmitted Cauliflower mosaic virus (CaMV) as a biological model, we confirm that the "noncirculative" mode of transmission dominant in plant viruses (designated "mechanical vector transmission" in animal viruses) involves extremely specific virus-vector recognition, and we identify an amino acid position in the "helper component" (HC) protein of CaMV involved in such recognition. Site-directed mutagenesis revealed that changing the residue at this position can differentially affect transmission rates obtained with various aphid species, thus modifying the spectrum of vector species for CaMV. Most interestingly, in a virus line transmitted by a single vector species, we observed the rapid appearance of a spontaneous mutant specifically losing its transmissibility by another aphid species. Hence, in addition to the first identification of an HC motif directly involved in specific vector recognition, we demonstrate that change of a virus to a different vector species requires only a single mutation and can occur rapidly and spontaneously.
Amino Acids↗
[Control of Chagas' disease in Guarani communities: knowledge and hygiene habits within the Project to Improve Living Conditions in Bolivia].
The aim of this study was to identify knowledge and control of vectorial transmission (Triatoma infestans, known as vinchuca) of Chagas' disease in Guaraní Communities in Bolivia. We performed a descriptive study of a series of 98 individuals through a semi-structured questionnaire. Interviewees were asked about their familiarity with vinchuca, whether they thought vinchuca produced disease, the name of the disease and its consequences, as well as behavior related to eliminating the domestic insect vectors, such as cleaning of the home, backyard and corral.The insect vector was sufficiently well known (98%), although the name of the disease was identified by only 14.3% of the interviewees. Although the dwellings favored insect proliferation, they were not frequently cleaned: 28.6% cleaned their homes while and 42.9% cleaned the backyard and 7.1% cleaned the corral. Gender differences were found in the division of labor: women cleaned the homes and backyards, while men clean the corral. Experience has shown that the usefulness of projects for building healthy living areas and for health education depends on the value given to these projects by the community. Women are probably the best target group, because they perform a greater number of preventive tasks and seldom leave the community for extended periods of time.
Adolescent↗
Cutaneous leishmaniasis in Egypt (review and comment).
Leishmania is primarily characterized by existing in two stages in its life cycle, each occurs in a distinct host. The amastigote stage found in the cytoplasm of the reticulo- endothelial cells, monocytes and other phagocytic cells of the vertebrate host. The promastigote stage found in the gut of its insect vector. The leishmaniasis comprise several diseases of wide diversity of manifestations caused by different species of the genus Leishmania. Because of the virtual morphological identity of the organisms throughout the genus, they are classified according to the clinical conditions which they produce in man, under three main headings: (1) Cutaneous leishmaniasis (CL.), (2) Mucocutaneous leishmaniasis (MCL.), (3) Visceral leishmaniasis (VL). Generally speaking, leishmaniasis is an example of a zoonosis that reaches man through an insect vector. The great majority of the Leishmania species are maintained by mammalian reservoir hosts in natural foci of infection. Rodents, dogs, wild cats, jackals, foxes, sloths, hyraxes and other carnivores are the animal reservoirs which maintain the infection in nature. The insect vectors are over 50 species of the genus Phlebotomus in the Old World and genus Lutzomyia in the New World.
Animals↗
Mobility of the piggyBac transposon in embryos of the vectors of Dengue fever (Aedes albopictus) and La Crosse encephalitis (Ae. triseriatus).
The re-emergence of arboviral diseases such as Dengue Fever and La Crosse encephalitis is primarily due to the failure of insect vector control strategies. The development of a procedure capable of producing stable germ-line transformants in the insect vectors of these diseases would bridge the gap between gene expression systems being developed to curb vector transmission and the identification of important genes and regulatory sequences and their reintroduction back into the insect genome in the form of vector control strategies. The transposable element piggyBac is capable of transposition in a variety of insect species, and could serve as a versatile insect transformation vector. Using plasmid-based excision and transposition assays, we report that this short-ITR transposon undergoes precise, transposase-dependent excision and transposition in embryos of Aedes albopictus and Aedes triseriatus, the vectors of Dengue fever and LaCrosse encephalitis, respectively. These assays allow us easily and rapidly to confirm and assess the potential utility of piggyBac as a gene transfer tool in a given species. piggyBac is an exceptionally mobile and versatile genetic transformation vector, comparable to other transposons currently in use for the transformation of insects. The mobility of the piggyBac element seen in both Ae. albopictus and Ae. triseriatus is further evidence that it can be employed as a germ-line vector in important insect disease vectors.
Aedes↗
[Insect-pest vectors as pathogenic carriers of microorganisms in objectives of health services].
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Animals↗
Partial characterisation of a trypanosome-lysing factor from the midgut of the desert locust, Schistocerca gregaria.
OBJECTIVE: Screening and biochemical characterisation of trypanosome-lysing factor (trypanolysin) from non-vector insect, Schistocerca gregaria. DESIGN: Laboratory based experiment. SETTING: Department of Biochemistry, University of Nairobi. RESULTS: Lysis of isolated trypanosomes was demonstrated with midgut homogenates of natural vector Glossina morsitans centralis as well in non-vector insects. The highest trypanolytic activity was observed in midgut homogenate of the desert locust. Schistocerca gregaria followed by the cockroach, Periplaneta americana (L). Further studies on the S. gregaria trypanolytic factor showed its proteinaceous nature due to its sensitivity to temperatures above 40 degrees C and to proteases. Additionally, the factor showed lectin-like properties since the activity was blocked by D-glucosamine. CONCLUSION: The trypanolytic factor has the potential of being used to modulate tsetse fly vectorial capacity.
Animals↗
The future of insect growth regulators in vector control.
Insect growth regulators (IGRs) are diverse groups of chemical compounds that are highly active against larvae of mosquitoes and other insects. The IGRs in general have a good margin of safety to most nontarget biota including invertebrates, fish, birds, and other wildlife. They are also relatively safe to man and domestic animals. The IGR compounds do not induce quick mortality in the preimaginal stages treated. Mortality occurs many days later after treatment. This is indeed a desirable feature of a control agent because larvae of mosquitoes and other vectors are an important source of food for fish and wildlife. On account of these advantages of IGRs and the high level of activity against target species, it is likely that IGRs will play an important role in vector control programs in the future.
Animals↗
Four cases of human filariosis due to Setaria labiatopapillosa found in Bucharest, Romania.
We record the occurrence of four cases of subconjunctival eye infection due to Setaria labiatopapillosa. The patients are all women, between 35 and 68 years old, all inhabitants of the same neighbourhood of the lake Pantelimon, a well known area for its blood feeding vector insect population and all complained about the same eye affliction: photophobia, eye swelling, tearing and foreign body sensation accompanied by some rash and low eosinofilia (6-8%). The treatment was surgical (excision) and DEC 1 mg/kg body weight. The vector insect cannot be specified. We stress that to our knowledge these are the first reported cases of human infection with Setaria labiatopapillosa.
Adult↗
[Expression of green fluorescent protein with baculovirus vector in insect cells].
The green fluorescent protein (GFP) gene was subcloned into the transfer vector pVLneo downstream of the polyhedrin gene (ocu) promoter. Insect cells were cotransfected with recombinant plasmid and Autographa californica Nuclear Polyhedrosis Virus (AcNPV) DNA. In the presence of G418, the recombinant virus containing GFP gene was purified. The GFP expressed in insect cells with a Mw of 30 kDa is observable by strong green light under a fluorescent microscope. Excitation and emission spectra of the GFP were 395 nm and 509 nm respectively. Integration of GFP gene on AcNPV genome was identified directly by Southern blot which gave strong hybridization signal between GFP cDNA probe and 1 kb EcoRI fragment of recombinant virus.
Animals↗
A nested-PCR assay for detection of Xylella fastidiosa in citrus plants and sharpshooter leafhoppers.
AIMS: Detection of Xylella fastidiosa in citrus plants and insect vectors. METHODS AND RESULTS: Chelex 100 resin matrix was successfully standardized allowing a fast DNA extraction of X. fastidiosa. An amplicon of 500 bp was observed in samples of citrus leaf and citrus xylem extract, with and without symptoms of citrus variegated chlorosis, using PCR with a specific primer set indicating the presence of X. fastidiosa. The addition of insoluble acid-washed polyvinylpyrrolidone (PVPP) prior to DNA extraction of insect samples using Chelex 100 resin together with nested-PCR permitted the detection of X. fastidiosa within sharpshooter heads with great sensitivity. It was possible to detect up to two bacteria per reaction. From 250 sharpshooter samples comprising four species (Dilobopterus costalimai, Oncometopia facialis, Bucephalogonia xanthopis and Acrogonia sp.), 87 individuals showed positive results for X. fastidiosa in a nested-PCR assay. CONCLUSIONS: The use of Chelex 100 resin allowed a fast and efficient DNA extraction to be used in the detection of X. fastidiosa in citrus plants and insect vectors by PCR and nested-PCR assays, respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: The employment of efficient and sensitive methods to detect X. fastidiosa in citrus plants and insect vectors will greatly assist epidemiological studies.
Animals↗
Iron metabolism in insect disease vectors: mining the Anopheles gambiae translated protein database.
All animals require iron for survival. This requirement reflects the role of this mineral as a cofactor of numerous proteins. However, under physiological conditions, Fe(2+) oxidizes to Fe(3+) encouraging the formation of toxic free radicals. In mammals, the potential for oxidative damage from iron is minimized by binding iron to proteins. Mammalian iron metabolism is complex and numerous proteins are involved in iron absorption, transport, uptake and utilization. We have analyzed the Anopheles gambiae translated protein database for candidates that show identity to proteins involved in mammalian iron metabolism (Holt et al., 2002. The genome sequence of the malaria mosquito Anopheles gambiae. Science 298, 129-149). Our results indicate that proteins involved in iron absorption and intracellular iron utilization are, for the most part, conserved in A. gambiae. In contrast, proteins involved in the pathways of iron export from the gut, transport in hemolymph and uptake at peripheral tissues in mosquitos differ from those for mammals.
Animals↗
Immune responses and parasite transmission in blood-feeding insects.
The detailed model of insect immunity being built for Drosophila, allied to mass sequencing programs for blood-feeding insects, has led to advances in our understanding of the interaction between pathogens and insect vectors. An outline of insect immunity is given here based on the Drosophila studies, which is used as a framework to discuss recent work on Plasmodium-mosquito and Trypanosoma-tsetse interactions.
Animals↗