Differences in saliva composition among three Brazilian populations of Panstrongylus megistus (Hemiptera, Reduviidae)

An updated insight into the Sialotranscriptome of Triatoma infestans: developmental stage and geographic variations

Background

Triatoma infestans is the main vector of Chagas disease in South America. As in all hematophagous arthropods, its saliva contains a complex cocktail that assists blood feeding by preventing platelet aggregation and blood clotting and promoting vasodilation. These salivary components can be immunologically recognized by their vector's hosts and targeted with antibodies that might disrupt blood feeding. These antibodies can be used to detect vector exposure using immunoassays. Antibodies may also contribute to the fast evolution of the salivary cocktail.

Methodology

Salivary gland cDNA libraries from nymphal and adult T. infestans of breeding colonies originating from different locations (Argentina, Chile, Peru and Bolivia), and cDNA libraries originating from F1 populations of Bolivia, were sequenced using Illumina technology. Coding sequences (CDS) were extracted from the assembled reads, the numbers of reads mapped to these CDS, sequences were functionally annotated and polymorphisms determined.

Main findings/Significance

Over five thousand CDS, mostly full length or near full length, were publicly deposited on GenBank. Transcripts that were over 10-fold overexpressed from different geographical regions, or from different developmental stages were identified. Polymorphisms were mapped to derived coding sequences, and found to vary between developmental instars and geographic origin of the biological material. This expanded sialome database from T. infestans should be of assistance in future proteomic work attempting to identify salivary proteins that might be used as epidemiological markers of vector exposure, or proteins of pharmacological interest.

Triatoma infestans is the main vector of Chagas disease in South America. As in all hematophagous arthropods, its saliva contains a complex cocktail that assists blood feeding by preventing platelet aggregation and blood clotting and promoting vasodilation. These salivary components can be immunologically recognized by their hosts and targeted with antibodies that might disrupt blood feeding. The respective antibodies can be used to detect vector exposure using immunoassays. On the other hand, antibodies may also contribute to the fast evolution of the salivary cocktail. In this work, we attempted to identify variations in the salivary proteins of T. infestans using Illumina technology that allowed identification of over five thousand proteins based on over 300 million sequences obtained from ten salivary gland libraries. This expanded sialome database from T. infestans should be of assistance in future work attempting to identify salivary proteins that might be used as epidemiological markers of vector exposure, or proteins of pharmacological interest.

Characterization of guinea pig antibody responses to salivary proteins of Triatoma infestans for the development of a triatomine exposure marker

Background

Salivary proteins of Triatoma infestans elicit humoral immune responses in their vertebrate hosts. These immune responses indicate exposure to triatomines and thus can be a useful epidemiological tool to estimate triatomine infestation. In the present study, we analyzed antibody responses of guinea pigs to salivary antigens of different developmental stages of four T. infestans strains originating from domestic and/or peridomestic habitats in Argentina, Bolivia, Chile and Peru. We aimed to identify developmental stage- and strain-specific salivary antigens as potential markers of T. infestans exposure.

Methodology and Principal Findings

In SDS-PAGE analysis of salivary proteins of T. infestans the banding pattern differed between developmental stages and strains of triatomines. Phenograms constructed from the salivary profiles separated nymphal instars, especially the 5^th instar, from adults. To analyze the influence of stage- and strain-specific differences in T. infestans saliva on the antibody response of guinea pigs, twenty-one guinea pigs were exposed to 5^th instar nymphs and/or adults of different T. infestans strains. Western blot analyses using sera of exposed guinea pigs revealed stage- and strain-specific variations in the humoral response of animals. In total, 27 and 17 different salivary proteins reacted with guinea pig sera using IgG and IgM antibodies, respectively. Despite all variations of recognized salivary antigens, an antigen of 35 kDa reacted with sera of almost all challenged guinea pigs.

Conclusion

Salivary antigens are increasingly considered as an epidemiological tool to measure exposure to hematophagous arthropods, but developmental stage- and strain-specific variations in the saliva composition and the respective differences of immunogenicity are often neglected. Thus, the development of a triatomine exposure marker for surveillance studies after triatomine control campaigns requires detailed investigations. Our study resulted in the identification of a potential antigen as useful marker of T. infestans exposure.

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, and currently affects approximately 8 million people in Latin American countries. Although vector control campaigns against the most effective Chagas disease vector, Triatoma infestans, have been highly successful, T. infestans is re-establishing in once-endemic regions. To monitor re-establishing triatomines, new epidemiological tools are needed. Antibody responses of hosts to triatomine salivary proteins represent a promising tool to detect biting bugs, and highly immunogenic salivary antigens may be used as markers of triatomine exposure. Therefore, we analyzed the antibody response of guinea pigs, common peridomestic hosts of T. infestans, to salivary proteins of nymphs and adults of four different T. infestans strains from Argentina, Bolivia, Chile and Peru. Developmental stage- and strain-specific proteins in the saliva of T. infestans influenced the antibody response of guinea pigs, and different salivary antigens were recognized by guinea pig sera. Despite the variations of immunogenic salivary antigens, a 35 kDa antigen was recognized by almost all guinea pig sera and this antigen may be a useful marker of T. infestans exposure.

Isolation and molecular characterization of a major hemolymph serpin from the triatomine, Panstrongylus megistus

Background

Chagas disease kills 2.5 thousand people per year of 15 million persons infected in Latin America. The disease is caused by the protozoan, Trypanosome cruzi, and vectored by triatomine insects, including Panstrongylus megistus, an important vector in Brazil. Medicines treating Chagas disease have unpleasant side effects and may be ineffective, therefore, alternative control techniques are required. Knowledge of the T. cruzi interactions with the triatomine host needs extending and new targets/strategies for control identified. Serine and cysteine peptidases play vital roles in protozoan life cycles including invasion and entry of T. cruzi into host cells. Peptidase inhibitors are, therefore, promising targets for disease control.

Methods

SDS PAGE and chromatograpy detected and isolated a P. megistus serpin which was peptide sequenced by mass spectrometry. A full amino acid sequence was obtained from the cDNA and compared with other insect serpins. Reverse transcription PCR analysis measured serpin transcripts of P. megistus tissues with and without T. cruzi infection. Serpin homology modeling used the Swiss Model and Swiss-PDB viewer programmes.

Results

The P. megistus serpin (PMSRP1) has a ca. 40 kDa molecular mass with 404 amino acid residues. A reactive site loop contains a highly conserved hinge region but, based on sequence alignment, the normal cleavage site for serine proteases at P1-P1′ was translocated to the putative position P4′-P5′. A small peptide obtained corresponded to the C-terminal 40 amino acid region. The secondary structure of PMSRP1 indicated nine α-helices and three β-sheets, similar to other serpins. PMSRP1 transcripts occurred in all tested tissues but were highest in the fat body and hemocytes. Levels of mRNA encoding PMSRP1 were significantly modulated in the hemocytes and stomach by T. cruzi infection indicating a role for PMSRP1 in the parasite interactions with P. megistus.

Conclusions

For the first time, a constitutively expressed serpin has been characterized from the hemolymph of a triatomine. This opens up new research avenues into the roles of serine peptidases in the T. cruzi/P. megistus association. Initial experiments indicate a role for PMSRP1 in T. cruzi interactions with P. megistus and will lead to further functional studies of this molecule.

Individual variability of salivary gland proteins in three Phlebotomus species

Pooled salivary gland samples are frequently used to ensure the sufficient amount of material for the experiments; however, this could mask an individual variability. Thus, we compared salivary protein profiles in seven colonies of three Phlebotomus species: Phlebotomus sergenti, Phlebotomus perniciosus, and Phlebotomus papatasi. Surprisingly, the individual profiles differed significantly between the colonies as well as between individuals. The highest variability was observed in proteins with molecular masses of 42-46 kDa corresponding to the yellow-related proteins. The phenogram constructed from salivary gland profiles revealed the existence of two main groups in P. sergenti, corresponding well with the geographical origin. The F1 progeny obtained from cross-mating studies between P. sergenti colonies of different geographical origin formed a distinct subgroup within the parental groups. In P. papatasi, several groups of protein profiles were observed with no relationship to the geographical origin. The biological role of salivary proteins variability is discussed.

Ecological patterns of blood-feeding by kissing-bugs (Hemiptera: Reduviidae: Triatominae)

Host use by vectors is important in understanding the transmission of zoonotic diseases, which can affect humans, wildlife and domestic animals. Here, a synthesis of host exploitation patterns by kissing-bugs, vectors of Chagas disease, is presented. For this synthesis, an extensive literature review restricted to feeding sources analysed by precipitin tests was conducted. Modern tools from community ecology and multivariate statistics were used to determine patterns of segregation in host use. Rather than innate preferences for host species, host use by kissing-bugs is influenced by the habitats they colonise. One of the major limitations of studies on kissing-bug foraging has been the exclusive focus on the dominant vector species. We propose that expanding foraging studies to consider the community of vectors will substantially increase the understanding of Chagas disease transmission ecology. Our results indicate that host accessibility is a major factor that shapes the blood-foraging patterns of kissing-bugs. Therefore, from an applied perspective, measures that are directed at disrupting the contact between humans and kissing-bugs, such as housing improvement, are among the most desirable strategies for Chagas disease control.

Antibody responses of domestic animals to salivary antigens of Triatomainfestans as biomarkers for low-level infestation of triatomines

Hematophagous arthropods such as Triatoma infestans, the vector of Trypanosoma cruzi, elicit host-immune responses during feeding. Characterization of antibody responses to salivary antigens offers the potential to develop immunologically based monitoring techniques for exposure to re-emergent triatomine bug populations in peridomestic animals. IgG-antibody responses to the salivary antigens of T.infestans have been detected in chickens as soon as 2 days after the first exposure to five adult bugs. Chickens and guinea pigs regularly exposed to this number of triatomines showed a significantly lower anti-saliva antibody titre than animals exposed to 25 adults and fifth instars of four different T.infestans strains originating from Bolivia and from Northern Chile. Highly immunogenic salivary antigens of 14 and 21kDa were recognised by all chicken sera and of 79kDa by all guinea pig sera. Cross-reactivity studies using saliva or salivary gland extracts from different hematophagous species, e.g. different triatomines, bed bugs, mosquitoes, sand flies and ticks, as well as chicken sera exposed to triatomines and mosquitoes, demonstrated that the 14 and 21kDa salivary antigens were only found in triatomines. Sera from peridomestic chickens and guinea pigs in sites of known T.infestans challenge in Bolivia also recognised the 14 and 21kDa antigens. These represent promising epidemiological markers for the detection of small numbers of feeding bugs and hence may be a new tool for vector surveillance in Chagas disease control programs.

Variability of the salivary proteins of 20 Brazilian populations of Panstrongylus megistus (Hemiptera: Reduviidae: Triatominae)

The objective of the present study was to study variability in the salivary proteins of 20 Panstrongylus megistus populations from different ecotopes and verify whether this variability influenced the intensity of the response to specific anti-saliva antibodies. Electrophoretic analysis of P. megistus saliva showed a complex protein composition and great interpopulation variability. A higher concentration of bands was observed in the 17-29 kDa region. The phenogram constructed from the electrophoretic profiles of the P. megistus study populations revealed the existence of two main groups. However, there was no evident relationship between these groups and geographical regions, ecotopes or hosts. Saliva inoculated by P. megistus during feeding elicited production of low level of anti-saliva antibodies in rabbit. The homologous and heterologous salivary proteins were recognised by serum of rabbit sensitised with saliva from only one population. Qualitative and quantitative differences were observed for recognised bands in the saliva of all eight populations studied by Western blot analysis. The most recognised bands were those of greatest molecular weight (68.0-97.4 kDa).

[Differences in the size of eggshells among three Pangstrongylus megistus colonies]

The objective of the study was to evaluate the measurements of eggshells from three colonies of P. megistus, two from the lab and one from a sylvatic habitat. Fifty eggshells from each colony were measured with the use of a stereoscopic microscope and the Qwin image analysis system,. The statistical analysis was performed using unpaired t-test in INSTAT program. The length, width and diameter of the opercular opening of the eggshells from the sylvatic colony were larger than the two laboratorial colonies of P. megistus.

Interpopulation variability among Panstrongylus megistus (Hemiptera: Reduviidae) from Brazil

Comparisons were made among Panstrongylus megistus (Burmeister) from three areas of Brazil (Bahia, Minas Gerais, and Santa Catarina), where populations differ with regard to their degree of association with human dwellings. The following characters were studied: morphology of the eggs and the male genitalia; morphometry of the head and thorax; isoenzyme profile; enzymatic activity of the alpha-glycerophosphate dehydrogenase (alpha-GPDH); and cytogenetics. In general, differences were observed in the weight, diameter, and length of the egg among Bahia, Minas Gerais, and Santa Catarina populations. Differences were not observed in the architecture of the egg exochorion. The size of the median process of the pygophore of the male genitalia of individuals from Bahia differed from the other two populations. The Minas Gerais population presented the largest number of denticles in the endosome process. The morphometry of the head and thorax differentiated Santa Catarina from the Bahia and Minas Gerais populations. Phosphoglucomutase (EC 5.4.2.2., PGM) was the only enzyme out of 11 that showed polymorphism; the population from Minas Gerais was most polymorphic, whereas the population from Santa Catarina was monomorphic. Study of the alpha-GPDH activity and cytogenetics did not reveal differences among the three populations. Analysis of all the characters studied together with information on these three populations from previous publications allowed a phenogram to be constructed. Two distinct groups were evident, one represented by Santa Catarina and the other by Bahia and Minas Gerais. Considering the greater variability of the Minas Gerais and Bahia populations, we propose the inclusion of these states within the area of origin of P. megistus.

Experimental evidence for a demographic cline in Panstrongylus megistus populations

The population biology of three populations of Panstrongylus megistus was compared to determine possible influence on the behaviour and epidemiological importance of this species. The results demonstrated differences in terms of egg eclosion time, nymphal mortality and development rates, and feeding and defaecation rates. These differences appeared to follow a geographical cline, primarily reflecting different degrees of adaptation to domestic habitats.