Modification of the Daily Activity Pattern of the Diurnal Triatomine Mepraia spinolai (Hemiptera: Reduviidae) Induced by Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) Infection.

Mepraia spinolai, (Porter) 1934, is a diurnal triatomine endemic to Chile and a wild vector of the protozoan Trypanosoma cruzi, (Chagas) 1909, which causes Chagas disease. Behavioral changes in M. spinolai induced by this parasite have been reported previously, which include detection of a potential host, defecation latency, and some life history traits. In this study we assessed changes in locomotor and daily activity due to infection with T. cruzi. No difference was detected in distance traveled between infected and uninfected individuals. However, the groups differed in their daily activity patterns; infected individuals showed significant reduction of movements during the light phase and concentrated their activity in the dark phase. Uninfected individuals showed no differences in locomotor activity between the phases. The results suggest that T. cruzi induces a displacement in the activity of M. spinolai toward the dark phase of the circadian cycle, which may improve its vector competence.

Feeding profile of Mepraia spinolai, a sylvatic vector of Chagas disease in Chile.

American trypanosomiasis is a chronic disease transmitted mainly by vectors. The hematophagous triatomine vectors transmit Trypanosoma cruzi to a wide variety of mammals, which usually are their food source. This study determined the feeding profile of Mepraia spinolai, a sylvatic triatomine vector, present in endemic areas of Chile. Vectors were captured in the north-central area of Chile. Samples of intestinal contents were analyzed by an Enzyme-linked immunosorbent assay (ELISA) that identifies and discriminates the presence of serum antigens from Homo sapiens and nine animal species (Canis familiaris, Felis catus, Capra hircus, Mus musculus, Gallus gallus, Octodon degus, Thylamys elegans, Phyllotis darwini and Oryctolagus cuniculus). Our data indicate the most frequent feeding source in this area was P. darwini, followed by O. degus, O. cuniculus, M. musculus, G. gallus, T. elegans, C. familiaris, F. catus and C. hircus. Mixed food sources were also identified.

Comparative population dynamics of the bug Mepraia spinolai, a sylvatic vector of Chagas' disease, in different hosts.

The aim of this work was to determine the impact of specific hosts on a population of Mepraia spinolai (Porter) (Hemiptera, Reduviidae), a sylvatic vector of Chagas' disease in Chile. We assessed whether a recently introduced host could be an important epidemiological factor in maintaining Chagas' disease in Chile. The study stressed the variations in survival, individual weight and fecundity in the insect population when the vector was raised with a species-specific food supply. The study compared the European rabbit Oryctolagus cuniculus, introduced in Chile

Predominance of Trypanosoma cruzi genotypes in two reservoirs infected by sylvatic Triatoma infestans of an endemic area of Chile.

We report results of Trypanosoma cruzi infection and parasite genotypes in the wild Octodon degus and synantropic reservoir Rattus rattus from an endemic area with sylvatic Triatoma infestans as the only detected vector. The infection status was determined by hemi-nested PCR directed to minicircles DNA and genotyping by hybridization tests with a panel of five specific probes, including two probes for TcI subgroups (clones 19 and 20). O. degus was found infected with 13.3% and mainly with sublineage TcIId, and less with TcIIb and TcI. Meantime the synantropic R. rattus was found infected with 27.7% and mainly with TcI and much less with TcIId, TcIIb and TcIIe. The results are discussed to explain the distribution of T. cruzi genotypes between these two reservoirs and the importance of sylvatic foci of T. infestans allowing the permanence of the wild and peridomestic cycle of Chagas disease.

Blood host sources of Mepraia spinolai (Heteroptera: Reduviidae), wild vector of chagas disease in Chile.

There are two vectors of the Chagas' disease in Chile: Triatoma infestans Klug the domestic vector and Mepraia spinolai Porter the sylvatic vector. The alimentary profile of M. spinolai has been poorly studied. In this work we study the participation of humans, goats, dogs, cats, rodents, rabbits, birds (hens) and reptiles in the diet of M. spinolai by analyzing the intestinal content through immunoradiometric assay. To put our results in a general context, we also compared the diet with that described for T. infestans. In decreasing order, we detected blood of rabbits, dogs, goats, rodents, humans, and birds (hens). There were 12.3% of insects infected with T. cruzi, but this fact was not significant for diet variance. In warm weather there was a larger diversity of alimentary sources than in a cold one. The niche breadth increased from 0.029 in cold weather to 0.464 in warm weather. The niche overlap of T. infestans and M. spinolai was 0.23.

[Situation of Mepraia spinolai, a wild vector for Chagas disease in Chile, in relation to others vectors from the perspective of their feeding profile]. / Situación de Mepraia spinolai, vector silvestre de la enfermedad de Chagas en Chile, en relación con otros vectores desde la perspectiva de sus fuentes de alimentación.

BACKGROUND: Three triatomine species, Triatoma infestans, Mepraia spinolai and Mepraia gajardoi, are vectors for Chagas disease in Chile. AIM: To compare the alimentary profile of Mepraia spinolai, the Chilean wild vector of Chagas disease, with that of the several other triatomines. MATERIAL AND METHODS: The alimentary profile of Mepraia spinolai was compared with that of other triatomines using cluster analysis (Q and R techniques) with the Jaccard index. RESULTS: Three basic groups of triatomines were identified: domestic, wild and specialists, such as P. coreodes and C. pilosa. Our wild vector M. spinolai was in an intermediate position between wild and domestic clusters, grouping with T. rubrovaria, T. sordida and P. megistus. The feeding sources, animals of the domestic and peri-domestic habitat and wild animals, corresponded to the clusters of the two groups. CONCLUSIONS: Mepraia spinolai, being a preponderantly wild species, approaches human dwellings and obtains food from domestic animals and eventually, from human blood (Rev Méd Chile 2000; 128: 1108-12).

Comparison of some behavioral and physiological feeding parameters of Triatoma infestans klug, 1834 and Mepraia spinolai porter, 1934, vectors of chagas disease in Chile

There are two vectors of Chagas disease in Chile: Triatoma infestans and Mepraia spinolai. We studied the feeding behavior of these species, looking for differences which could possibly explain the low impact of the latter species on Chagas disease. Both species used thermal cues to locate their feeding source and consumed a similar volume of blood which was inversely related to the body weight before the meal and directly related to the time between meals. The average time between bites were 6.24 and 10.74 days. The average bite of M. spinolai lasted 9.68 min, significantly shorter than the 19.46 min for T. infestans. Furthermore, while T. infestans always defecated on the host, this behavior was observed in M. spinolai in only one case of 27 (3.7 per cent). The delay between the bites and defecation was very long in M. spinolai and short in T. infestans. These differences may affect the reduced efficiency of transmission of Chagas infection by M. spinolai.

Population parameters of Triatoma spinolai (Heteroptera: Reduviidae) under different environmental conditions and densities.

Population parameters of Triatoma spinolai Porter were studied using specimens collected in the north and central region of Chile. Two cohorts of 17 and 44 first instars were maintained at a constant temperature of 28 degrees C and 70% RH. Two similar cohorts of bugs were exposed to 16-24 degrees C and 55-75% RH and maintained under a photoperiod of 14:10 (L:D) h for 16 mo. The preimaginal period ranged between 285 and 372 d under constant conditions. The lower-density cohort required 9.5 mo to reach the adult stage compared with 12.4 mo for the high-density cohort. Bugs placed under variable temperature and relative humidity conditions did not survive long. Cohorts with higher densities had similar mortality rates with greater mortality occurring in cohorts that had lower numbers of bugs. Cohorts under constant temperature and relative humidity reproduced and basic reproduction rates (Ro, intrinsic growth rate [r], and generation time [G]) were estimated. Cohorts with higher numbers of bugs had higher Ro and r, whereas values of G were similar for both groups. Apparently, 25 degrees C was a critical temperature threshold for T. spinolai and there appeared to be a minimal population density that allowed reproduction.

Assessing the impact of disease vectors on animal populations.

Many studies have attempted to assess the relative effects of different vectors of a disease on animal populations. To this end, three measures have been proposed: Vectorial efficiency, Vectorial capacity and recently Vectorial effectiveness (or Vectorial impact). In this study we relate these measures to derive some of their properties emphasising in the vectorial impact for its importance in both, population performance of parasites and the proportion of the prevalence of one parasite due to a given vector. We applied the quantitative expressions advanced in this study to a simple Chilean example with one parasite (Trypanosoma cruzi), two vectors (Triatoma infestans and Mepraia spinolai) and one animal population (humans: Chagas's disease).

Preliminary studies on temperature selection and activity cycles of Triatoma infestans and T. spinolai (Heteroptera:Reduviidae), Chilean vectors of Chagas' disease.

Preferred temperature and activity patterns of Triatoma infestans Klug and Triatoma spinolai Porter were studied, both are vectors of Chagas' disease in Chile. In the laboratory, 24 T. spinolai and 18 T. infestans were exposed to a temperature gradient between 50 and 15 degrees C and a photoperiod of 14:10 (L:D) h. Temperature and hourly position of bugs in an experimental chamber were recorded for 24 h. Both species showed a cycle of preferred temperature, and both selected higher temperatures beginning at 1600 hours, although T. infestans maintains this preference over a longer period. For both species, activity patterns were synchronized with the light-dark cycle, although these activity rhythms were significantly different. T. spinolai had higher activity during the photophase, and T. infestans showed a lower activity in the photophase and a higher one during the scotophase. The similar pattern of preferred temperatures may facilitate the selection of similar environments in the event of colonization of houses by T. spinolai. Diurnal activity of this species might be a disadvantage (in terms of more exposure to defensive responses of the vertebrate hosts) but may allow T. spinolai to share the same habitat with T. infestans without competitive interference.

[Tripano-triatomine infection of Triatoma spinolai in a zone with epidemiological risk]. / Infección tripano-triatomina de Triatoma spinolai en una zona de riesgo epidemiológico.

BACKGROUND: Triatoma spinolai is the only wild vector for Chagas disease in Chile and its epidemiological importance is being studied. AIM: To study the proportion of insects infected with Trypanosoma cruzi (tripano-triatomine index) in a zone with epidemiological risk in the Metropolitan Region of Chile. METHODS: Four hundred ninety two specimens of Triatoma spinolai were collected in four sites of a quarry zone, 14 kilometers north of Santiago. Their maturity and the presence of Trypanosoma cruzi in their intestinal contents were determined. RESULTS: Mean tripano-triatomine index was 26.02 +/- 2% (range 0 to 34% in different sites). The proportion of infected insects increased along with their maturity and 58% of adult specimens were infected. There was a seasonal variation of the proportion of infected specimens, being lower in March and June and higher in July and February. CONCLUSIONS: The studied zone has a potential epidemiological risk for the transmission of Chagas disease by Triatoma spinolai.

[Compared dynamics of Triatoma infestans cohorts in residential environment]. / Dinámica comparada de cohortes Triatoma infestans en ambiente habitacional.

Triatoma infestans is an insect with a high colonization capacity, capable of maintaining populations near saturation levels in different environments. However, it has a great lability in its population parameters when exposed to variable environmental conditions. The aim of this work was to explore the response of two cohorts with 4 initial egg densities, in two environmental conditions ("shelter" at 24 +/- 2.7 degrees C and 73 +/- 7% of relative humidity and "room" at 16.9 +/- 2.1 degrees C and 69.8 +/- 5% of relative humidity), similar to those commonly found in houses at Santiago, Chile. The proportion of fertile egg was higher in shelter conditions (93.7 vs 74.6%). Survival curves were similar in both environments and mortality was not influenced by density or maturity of individuals. Maturation was retarded in both environment, specially in the colder one, compared to constant environments. It is concluded that maturation of T infestans is the most affected parameter in the unprotected environment. Even though, considering the insect's longevity, its reproductive function is probably accomplished. The great lability of T. infestans population parameters, suggests that the finding of favorable microenvironments is essential for their survival.

[Dynamics of Chagas infection transmission in Chile: model and simulation]. / Dinámica de transmisión de la infección chagásica en Chile: modelo y simulación.

Triatoma infestans is the principal vector for Chagas disease in Chile. Although there is enough epidemiological information about human infection, the effect of vector and host (animals and man) populations interrelations over Chagas disease prevalence has not been studied. This work studies a determinist mathematical model for the dynamics of Chagas disease transmission by Triatoma infestans, relating entomological population parameters with infection propagation. The effect of invasion of susceptible animal and human populations by infected triatomine insects and the stability of Chagas disease endemic was simulated. The Ro parameter was estimated. This is a gross appraiser of the infection reproductive rate that relates triatomine insect density, bite rate and mortality. The infected population at equilibrium was estimated. The resulting endemic was highly stable with a great amount of chronic and few acute cases. There is always an acute Chagas epidemic stage after a recent invasion. The need for a threshold triatomine insect population for the genesis of an endemic is proposed.

[Population effects of fluctuation in fecundity and mortality in Triatoma infestans: simulation using Leslie matrices]. / Effectos poblacionales de fluctuaciones de la fecundidad y la mortalidad de Triatoma infestans: simulacion mediante matrices de Leslie.

The population effects of known fluctuations in fecundity and mortality of T. infestans was studied through simulation using Leslie matrices. The effect of mortality and fecundity cycles was a stepped cycling through the growing phase, with no significant population decreases. Density dependent regulation stabilizes changes during the steady phase. The main effect is on population composition with the establishment of a regular annual cycle in the proportion of different age groups. Cycles with high number of larvae may be misinterpreted as an adult plague.

[Biology of Triatoma infestans populations: fluctuations of fecundity and mortality]. / Biología de poblaciones de Triatoma infestans: fluctuaciones de la fecundidad y la mortalidad.

Fecundity and mortality in population of insects is relevant to the epidemiology of insect transmitted diseases. These variables were studied for T. infestans during 5 years under constant conditions of temperature, relative humidity, light periods and individual density. Mean fecundity was 0.96 +/- 0.69 eggs/female-week, range 0 to 4. Minima were observed in april and maxima in october and november. Mean mortality of intermediate forms was 0.058 +/- 0.031/individual-week, range 0.009 to 0.135, similar for females and males. Minima for mortality were observed in june and july, maxima from november to march. Fluctuations of fecundity are attributed to endogenous cyclic changes related to mating and egg laying. Possible explanations for fluctuations in mortality include the action of infectious agents. The secondary mortality cycle may be related to delayed effect of population density or to differential mortality of cohorts born under different environmental conditions.