Effects of Trypanosoma cruzi on the phenoloxidase and prophenoloxidase activity in the vector Meccus pallidipennis (Hemiptera: Reduviidae)

Abstract

BackgroundTriatomine insects are vectors of Trypanosoma cruzi, the causal agent of Chagas disease. The insect-parasite interaction has been studied in relation to the transmission and prevalence of this disease. For most triatomines, however, several crucial aspects of the insect immune response are still unknown. For example, only for Rhodnius prolixus and Triatoma infestans has the activity of phenoloxidase (PO) and its zymogen prophenoloxidase (proPO) been reported in relation to the hemolymph and anterior midgut (AM). The aim of this study was to gain insight into the immune response to T. cruzi infection of an important triatomine in Mexico, Meccus pallidipennis.MethodsParasites were quantified in the rectal contents of infected M. pallidipennis groups. We examined some key factors in disease transmission, including the systemic (hemolymph) and local (gut) immune response.ResultsParasites were present in the rectal contents at 4 days post-infection (pi) and reached their maximum density on day 7 pi. At 7 and 9 days pi mainly metacyclic trypomastigotes occurred. Compared to the control, the infected insects exhibited diminished PO activity in the hemolymph on days 9, 16 and 20 pi, and in the AM only on day 9. Additionally, infected insects displayed lower proPO activity in the hemolymph on day 1, but greater activity in the AM on day 28.ConclusionsThe parasite strain originating from M. pallidipennis rapidly colonized the rectum of nymphs of this triatomine and developed high numbers of metacyclic trypomastigotes. Neither the changes of concentrations of PO and proPO in the hemolymph nor in the AM correlated with the changes in the population of T. cruzi.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3016-0) contains supplementary material, which is available to authorized users.

Activity of the prophenoloxidase system and survival of triatomines infected with different Trypanosoma cruzi strains under different temperatures: understanding Chagas disease in the face of climate change

“…The strain ITRI/MX/12/MOR (further referred to as Morelos) was obtained from a male M. pallidipennis specimen captured and isolated in 2012 in Cuernavaca, Morelos, Mexico. This strain has been characterized as TcI [45]. The strain ITRI/MX/14/CHIL (further referred to as Chilpancingo) was obtained from a female M. pallidipennis specimen captured and isolated in 2014 in Chilpancingo, Guerrero, Mexico.…”

“…For each strain, 150 nymphs were infected by allowing them to feed from mice that had been inoculated with 20,000 T. cruzi metacyclic trypomastigotes/ml 15 days before, to ensure that the parasite was in the exponential stage of growth [45]. Additionally, 150 nymphs were allowed to feed from non-infected female CD-1 mice of the same weight (15–18 g), to be used as a control group.…”

“…After 15 days of incubation, the rectal content of each specimen was obtained by abdominal compression and examined by direct observation to confirm the presence of T. cruzi blood trypomastigotes [45]. A drop of PBS 1× pH 7.2 (Na 2 HPO 4 8 × 10 −6 M, KH 2 PO 4 10 −6 M, KCl 3 × 10 −6 M, NaCl 10 −4 M) was placed on a glass slide.…”

“…A drop of PBS 1× pH 7.2 (Na 2 HPO 4 8 × 10 −6 M, KH 2 PO 4 10 −6 M, KCl 3 × 10 −6 M, NaCl 10 −4 M) was placed on a glass slide. A drop of triatomine rectal content was added and the mixture was homogenized [45]. A 10-μl aliquot was taken and microscopically observed under a 40× objective (Olympus CH-2, Center Valley, PA, USA).…”

“…The prophenoloxidase (proPO) and phenoloxidase (PO) enzymatic cascade is known to be a key element in the immune response associated to the defense against pathogens and their removal [43–46]. In this regard, proPO and PO activity in M. pallidipennis were found associated after one week of infection with T. cruzi [45].…”