Excito-repellency effect of deltamethrin on triatomines under laboratory conditions.

This work demonstrates that deltamethrin in low doses produces an excito-repellency effect on triatomines, as already observed for mosquitoes. A wooden box covered with a cloth impregnated with deltamethrin at doses of 2.5 and 5mg ai/m2 was utilized for the experiment. The triatomine species studied were Triatoma infestans, Panstrongylus megistus, Rhodnius neglectus and Triatoma sordida. Adults were released in one of the sides of the box and their position was noted in subsequent periods. The observations were realized on the day the cloth was impregnated and subsequently repeated at 30 and 60 days for T. sordida; on day 120, the remaining species were included. Insect mortality and attempts at flight from the box were also observed. Excito-repellency was evident for all species and doses up to day 120. The only species that attempted to fly was P. megistus. The excito-repellency effect may be considered as an additional advantage to the insecticide power, as it should be able to prevent the installation of new colonies by females that fly into the homes, and at the moment of the spraying, it should promote the flushing out of triatomines from the wall crevices and from other shelters.

Comparative kinetics of bloodmeal intake by Triatoma infestans and Rhodnius prolixus, the two principal vectors of Chagas disease.

Chagas disease vector insects Triatoma infestans and Rhodnius prolixus (fifteen stage III nymphs per 4 litre cage) were allowed to feed on anaesthetized mice for 1 h (control group), or on active non-anaesthetized mice (NAM) for 2, 4 or 8 h exposure. The bloodmeal size (weight increase) for both species was proportional to the duration of contact with NAM, due to ingestion of multiple small bloodmeals, up to 142% of control weight for T. infestans with 8 h exposure to NAM. The mean weight increase of T. infestans nymphs after 4 h contact with NAM was similar to that of the control group, whereas for R. prolixus, 8 h contact with NAM gave only 64% of the control value. For both species of insect, within 4 h of feeding, > 20% of the bloodmeal weight was lost by defaecation and diuresis. The proportions of unfed nymphs and mortality during 2 h contact with NAM were significantly higher for R. prolixus, demonstrating better exploitation of the host blood source by T. infestans, apparently because during blood-feeding the latter insect species caused less irritation to the host.

A role for lymphocytes and cytokines on the eosinophil migration induced by LPS.

In the present work we review the existing evidence for a LPS-induced cytokine-mediated eosinophil accumulation in a model of acute inflammation. Intrathoracic administration of LPS into rodents (mice, rats or guinea pigs) induces a significant increase in the number of eosinophils recovered from the pleural fluid 24 hr later. This phenomenon is preceded by a neutrophil influx and accompanied by lymphocyte and monocyte accumulation. The eosinophil accumulation induced by LPs is not affected by inhibitors of cyclo or lipoxygenase nor by PAF antagonists but can be blocked by dexamethasone or the protein synthesis inhibitor cycloheximide. Transfer of cell-free pleural wash from LPS injected rats (LPS-PW) to naive recipient animals induces a selective eosinophil accumulation within 24 hr. The eosinophilotactic activity present on the LPS-PW has a molecular weight ranging between 10 and 50 kDa and its effect is abolished by trypsin digestion of the pleural wash indicating the proteic nature of this activity. The production of the eosinophilotactic activity depends on the interaction between macrophages and T-lymphocytes and its effect can not be blocked by anti-IL-5 monoclonal antibodies. Accumulated evidence suggest that the eosinophil accumulation induced by LPS is a consequence of a eosinophilotactic cytokine produced through macrophage and T-cell interactions in the site of a LPS-induced inflammatory reaction.

Anticoagulant activity of Triatoma infestans and Panstrongylus megistus saliva (Hemiptera/Triatominae).

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.

Triatoma infestans is more efficient than Panstrongylus megistus in obtaining blood meals on non Anaesthetized mice

We compared the influence of the bug density in the capacity of Triatoma infestans and Panstrongylus megistus in obtaining blood meal in non anaesthetized mice. The regression anlysis for increase in body weight (mg) versus density (no. of bugs/mouse) showed that in experiments with anaesthetized mice (AM), no correlation was observed. In experiments with non anaesthetized mice (NAM) the weight increase was inversely proportional to density. The regression slope for blood meal size on density was less steep for T. infestans than for P. megistus (-1.9 and -3.0, respectively). The average weight increase of P. megistus nymphus in experiments with AM was higher than for T. infestans nymphs; however, in experiments with NAM such results were inverted. Mortality of P. megistus was significantly higher than of T. infestans with NAM. However, in experiments with AM very low mortality was observed. Considering the mortality and the slope of regression line on NAM, T. infestans is more efficient than P. megistus in obtaining blood meal in similar densities, possibly because it caused less irritation of the mice. The better exploitation of blood source of T. infestans when compared with P. megistus in similar densities, favours the maintenance of a better nutritional status in higher densities. This could explain epidemiological findings in which T. infestans not only succeeds in establishing larger colonies but also dislodges P. megistus in human dwellings when it is introduced in areas where the latter species prevails.

Triatoma infestans is more efficient than Panstrongylus megistus in obtaining blood meals on non anaesthetized mice.

We compared the influence of bug density in the capacity of Triatoma infestans and Panstrongylus megistus in obtaining blood meal in non anaesthetized mice. The regression analysis for increase in body weight (mg) versus density (no. of bugs/mouse) showed that in experiments with anaesthetized mice (AM), no correlation was observed. In experiments with non anaesthetized mice (NAM) the weight increase was inversely proportional to density. The regression slope for blood meal size on density was less steep for T. infestans than for P. megistus (-1.9 and -3.0, respectively). The average weight increase of P. megistus nymphs in experiments with AM was higher than for T. infestans nymphs; however, in experiments with NAM such results were inverted. Mortality of P. megistus was significantly higher than that of T. infestans with NAM. However, in experiments with AM very low mortality was observed. Considering the mortality and the slope of regression line on NAM, T. infestans is more efficient than P. megistus in obtaining blood meal in similar densities, possibly because it caused less irritation of the mice. The better exploitation of blood source of T. infestans when compared with P. megistus in similar densities, favours the maintenance of a better nutritional status in higher densities. This could explain epidemiological findings in which T. infestans not only succeeds in establishing larger colonies but also dislodges P. megistus in human dwellings when it is introduced in areas where the latter species prevails.

[Feeding and defecation dynamics of Triatoma sordida]. / Dinâmica da alimentação e dejeção do Triatoma sordida.

Today, Triatoma sordida is the most frequently captured triatomine in Brazil. For a better understanding of its vectorial potential, its feeding dynamics and dejections behaviour were studied in comparison with Triatoma infestans and P. megistus. The proportion of T. sordida and T. infestans that blood fed on anaesthetized rats did not differ significantly. There was no significant difference in the time elapse between release of the bugs and the initiation of blood feeding. The mean time between completion of a blood meal and the first dejection was significantly lower in T. infestans than in T. sordida. The numbers of insects that defecated during the blood meal or immediately afterwards was similar for both species. Approximately 80 specimens of each of T. sordida, T. infestans and Panstrongylus megistus were offered daily blood meals for 30 minutes, over a period of 30 days. T. sordida bit more frequently than did P. megistus and T. infestans. These data could indicate that T. sordida may not be completely adapted to its host and might have difficulty in complete its blood meal.