Trypanosoma cruzi infection reduces the population fitness of Mepraia spinolai, a Chagas disease vector.

The hematophagous insect Mepraia spinolai (Hemiptera: Reduviidae: Triatominae) is naturally infected with the protozoan parasite Trypanosoma cruzi, the agent of Chagas disease in humans. In this study, we compared the demographic parameters of M. spinolai with and without T. cruzi infection. We collected the immature life table data of 479 M. spinolai individuals of control cohort (reared on mice without T. cruzi infection) and 563 M. spinolai individuals of treatment cohort (reared on mice with T. cruzi infection). Nymphs were maintained in individual compartments inside a growth chamber (26°C; 65-75%) until adult emergence; moulting and survival were recorded daily. For the adult life table study of the control, we used 24 pairs of adults from the control cohort. For the adult life table study of T. cruzi-infected cohort, 25 infected females were paired with 25 males from the control cohort. Life table data were analysed using bootstrap-match technique based on the age-stage, two-sex life table. The preadult survival rate (0.5282) of the control cohort was significantly higher than that of the infected cohort (0.2913). However, the mean fecundity of reproductive females (Fr = 22.29 eggs/♀) and net reproductive rate of population (R0 = 5.07 offspring/individual) of the 0.5th percentile bootstrap-match control cohort were not significantly different from those of the infected cohort (Fr = 23.35 eggs/♀, R0 = 3.77 offspring/individual). Due to the shorter total preoviposition period and higher proportion of reproductive female, the intrinsic rate of increase (r = 0.0053 d-1 ) and finite rate of increase (λ = 1.0053 d-1 ) of control cohort of M. spinolai were significantly higher than those of the T. cruzi-infected cohort (r = 0.0035 d-1 , λ = 1.0035 d-1 ). These results suggest that T. cruzi infection reduces the population fitness of the Chagas disease vector M. spinolai.

Opportunistic or selective? Stage-dependent feeding behavior in a wild vector of Chagas disease.

The composition and contribution of different host species in the dynamics of vector-borne zoonotic parasites are particularly relevant for public health. Hence, the study of host selection by vectors is fundamental. Developmental stage and infection status are factors that may modulate vector feeding behavior. In the semi-arid Mediterranean ecosystem of South America, the transmission of Trypanosoma cruzi, the protozoan causing Chagas disease, includes the triatomine vector Mepraia spinolai and several vertebrate species. In this field study, we examined whether M. spinolai exhibits an opportunistic feeding behavior dependent upon developmental stage and/or infection status. We found that M. spinolai does not feed according to the relative availability of vertebrate species. In addition, early stage nymphs (first/second instars) fed on twice as many different species as middle (third/fourth instars) and late (fifth instars and adults) M. spinolai, with the former feeding on native rodents and lizards and the latter mostly on rabbits. Infected and uninfected M. spinolai showed similar feeding profiles. Wild triatomine species might be described as stage-dependent selective blood feeders, as a consequence of the temporal and spatial scale at which host-vector interactions occur, highlighting that all developmental stages might be infected and capable of transmitting T. cruzi.

Trypanosoma cruzi could affect wild triatomine approaching behaviour to humans by altering vector nutritional status: A field test.

Hematophagous insects exhibit complex behaviour when searching for blood-meals, responding to several host stimuli. The hematophagous insect Mepraia spinolai is a wild vector of Trypanosoma cruzi, causative agent of Chagas disease in humans, in the semiarid-Mediterranean ecosystem of Chile. In this study, we evaluated the association between the approaching behaviour to a human host, with T. cruzi infection status and nutritional condition of M. spinolai. To this end, we captured 501 individuals in six consecutive 10 min-timespan, using a human as bait. Captured vectors were weighed, photographed and measured to calculate their nutritional status by means of a Standardized Body Mass Index. Trypanosoma cruzi infection was assessed in the intestinal content by using a real-time PCR assay. Ordinal logistic regressions were performed separately for infected and uninfected groups to evaluate if the nutritional status was associated with the approaching behaviour to a human host, recorded as the time-span of capture. Nutritional status of uninfected triatomines was higher than that from infected ones (p < 0.005). Among the infected, those with higher nutritional status approached first (p < 0.01); there was no effect of nutritional status in the uninfected group. Trypanosoma cruzi infection might affect the foraging behaviour of M. spinolai under natural conditions, probably deteriorating nutritional status and/or altering vector detection abilities.