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Escaping the complement system is an important step in the establishment of infections. Some pathogens have acquired the ability to inactivate the complement system to ensure successful infection. This has been observed in parasites from the genus Leishmania, which inactivate C3b molecules deposited on their surface through the membrane protease GP63. In the present study, we describe a new mechanism that also acts through C3b inactivation. This mechanism involves the binding of the complement regulatory molecule factor H from serum. Factor H signals a plasma protease (factor I) to inactivate C3b molecules deposited on the surface of the parasites. According to our results, Leishmania infantum, L. amazonensis, and L. braziliensis recruit factor H from human serum. The absorption of factor H by L. infantum was studied in detail to better understand how it works. L. infantum binds factor H from human serum and factor H-like proteins from dog serum. When exposed to purified factor H, promastigotes bind this regulatory molecule and inactivate C3b in the presence of factor I. This indicates the existence of an as yet unidentified factor H-binding outer surface molecule functioning as a receptor. The two mechanisms (GP63 and factor H binding) work independently, as Leishmania promastigotes with inhibited GP63 can easily inactivate C3b molecules on the surface of the parasite. The identification of the factor H receptor could lead to the development of a vaccine target for leishmaniasis control, as blocking antibodies to factor H binding could impair the mechanism of C3b inactivation, making the parasite more susceptible to the complement system.

International audience; It has been largely assumed that the individual experience of disease vector insects may affect host choice and, as a consequence, have an important influence on parasite transmission. In particular, it is speculated that vector insects should be able to learn and remember the most and/or less defensive hosts, shifting their preference accordingly. Nevertheless, despite the invested efforts in testing the capacity to learn and remember information of blood-sucking insects, only little conclusive information has been obtained hitherto. Recently, the ability of Rhodnius prolixus to associate a behaviourally neutral odour to the perspective of either obtaining a blood-meal or being punished has been demonstrated, the same odour becoming attractant or repellent for the bugs, respectively, according to the individual previous experience. The present work represents a step forward in the study of the cognitive abilities of Chagas disease vectors and their influence on host choice. We tested whether or not bugs bias their choice for a host based on the association of its odour with a negative experience. Our results show that whereas naïve bugs presented no preference when confronted to the odour of two different hosts, bugs previously exposed to the contingency of the odour of one host and a mechanical perturbation mimicking defensive behaviour, biased their preference towards the other host. This constitutes the first evidence of olfactory conditioning to host odours in triatomine bugs, vectors of Chagas disease and one of the few available up to date on haematophagous insects. The epidemiological significance of this finding is discussed.

Comparisons of electrophoretic profiles of triatomines (Panstrongylus megistus) from the Brazilian states of Bahia (BA), Minas Gerais (MG) and Santa Catarina (SC) revealed differences in the composition of the saliva between the three populations. A phenogram constructed on the basis of the most representative electrophoretic banding patterns allowed the specimens tested to be divided into two groups. The BA and SC populations could be completely separated while some individuals from MG could be placed in each group. The BA population presented fewer bands than the MG and SC ones. The populations studied also differed with regard to their degree of association with human habitations (sylvatic, peridomiciliary and/or intradomiciliary) and our results suggest that the proteinaceous composition of the saliva of the three distinct populations of triatomines could be related to the hosts each is likely to encounter.

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).

Salivary gland extract of Triatoma infestans prolonged thrombin time, prothrombin time, and activated partial thromboplastin time, while salivary gland extract of Panstrongylus megistus delayed thrombin time and activated partial thromboplastin time. However, saliva of P. megistus prolonged activated partial thromboplastin time and saliva of T. infestans delayed activated partial thromboplastin time and prothrombin time. T. infestans saliva interferes particularly with activity of factor VIII (intrinsic pathway) and factor V (common pathway), but also affects other factors. Saliva of the triatomine species studied presented distinct SDS-PAGE profiles. These results demonstrate that there are differences in anticoagulant activity and protein composition of triatomine saliva.