The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cruzi in Triatoma infestans (Insecta, Hemiptera).

The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cruzi, which colonise the intestinal tract of the blood-sucking bug Triatoma infestans, was investigated. In established infections of controls without azadirachtin treatment, the small intestine of fifth-instar T. infestans contained up to 7 x l0(6) B. triatomae and the rectum 3 x 10(6). In comparison to this homoxenous flagellate, the population densities of T. cruzi in the respective regions were 99.3 and 76% lower. Treatment with azadirachtin (1 microg ml(-1)) via a blood meal and a concurrent infection with B. triatomae resulted in an increase of the population density (3 weeks p.i.), caused mainly by the mastigote stages in the rectum. In an established B. triatomae infection (12 weeks p.i.), feeding of azadirachtin did not affect the population density and composition. In an optimal T. cruzi-vector system, i.e. parasite and bug originate from the same locality, the treatment with azadirachtin at 20 weeks p.i. strongly reduced the population density in the small intestine of all bugs up to 100 days after treatment, but only in a minor percentage of the bugs in the rectum. Trypanosoma (cruzi incubated for up to 24 h in faeces of azadirachtin-treated bugs were not affected, indicating that the rectum of these bugs contained no toxic substances. The importance of these findings is that investigations of the mechanisms of action of azadirachtin offer a possibility to identify vector-derived compounds, which are necessary for the development of T. cruzi, thereby, giving us a possible new strategy to combat Chagas' disease.     

The effect of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bug Triatoma infestans: influence of group size

Developmental time and mortality in uninfected larvae of the reduviid bug Triatoma infestans and in those infected by feeding a mixture of blood and cysts of the homoxenous trypanosomatid Blastocrithidia triatomae were compared. Larvae were maintained isolated in 77-cm3 (area 9.6 cm2) beakers or in groups of 20, 30, 40, and 50 bugs per 1-liter beaker (area 722 cm2). In uninfected groups, only a minor proportion of isolated bugs showed delayed development, but in groups infected with B. triatomae, additionally, a retardation in groups of 50 larvae occurred. Infected bugs needed more time to complete development in fourth and fifth instar than did uninfected bugs. Mean mortality rates of about 10% in uninfected groups were unaffected by group size. Mortality rates in most groups of infected bugs were about 50%, but in groups consisting of 50 larvae a statistically significant higher mortality rate of 75% was observed. This indicates a subpathological overcrowding stress, increased by the synergistic action of the flagellate.     

Scanning Electron Microscopic Studies of Blastocrithidia triatomae (Trypanosomatidae) in the Rectum of Triatoma infestans (Reduviidae)12

ABSTRACT. The morphology of Blastocrithidia triatomae, when colonizing the rectum of Triatoma infestans, was studied by scanning electron microscopy. The posterior end of the epimastigote's body is tapered and often rolled up. The “straphangers” (cyst stages) are connected with the flagellum by “cytoplasmic bridges”; after “straphanger” detachment these bridges persist as remnants. A comparison of colonization densities of B. triatomae and Trypanosoma cruzi shows that both prefer to colonize the rectal gland, but minor density differences are apparent for B. triatomae in other rectal regions. The colonization density in established infections of B. triatomae is always greater than that of T. cruzi, especially near the midgut exit.     

Pathological effects of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bug Triatoma infestans after infection by membrane feeding and long-term starvation

Developmental time and mortality in larvae of the reduviid bug Triatoma infestans were studied in uninfected groups and in those infected with Blastocrithidia triatomnae by in vitro feeding with 10(4) cyst stages/cm(3) blood. Bugs were subsequently subjected to two different starvation periods. In bugs fed at weekly intervals infection with B. triatomae was associated with developmental retardation, increasing in the final instars, and with increased mortality in the third and preadult instar. Compared to these groups, long-term starvation caused slightly lower mortality rates of uninfected groups and in infected bugs a remarkably higher mortality rate in the preadult instar. Total mortality rates of infected groups were nearly unaffected by starvation.     

Developmental time and mortality of the reduviid bug Triatoma infestans with differential exposure to coprophagic infections with Blastocrithidia triatomae (Trypanosomatidae)

Developmental time and survival in larvae of the reduviid bug Triatoma infestans were studied in uninfected groups and in those exposed to a coprophagic infection with Blastocrithidia triatomae. Addition to young uninfected larvae of (a) different numbers of infected bugs, (b) infected and uninfected bugs, and (c) fresh or dry infectious feces were compared. Retardation of development was evident in groups given infected larvae or fresh feces. Mortality rates were correlated with infection rates and were higher in groups given more infected bugs, independent of the presence of uninfected bugs. Therefore, bugs did not discriminate between feces from infected and uninfected bugs, or they did not reject infectious feces. Dry feces had to be redissolved with fresh feces before infection was possible.     

The biting rate of Triatoma infestans in Argentina

1. The daily proportion of fed individuals in a population of the reduviid bug Triatoma infestans (Klug), maintained under natural climatic conditions in experimental chicken houses in central Argentina, was estimated from the proportion of bugs retaining colourless urine in the rectum. 2. From the estimates of feeding frequency throughout a 1 year period, it was shown that temperature has a dominant effect on biting rate, but density-dependent effects became apparent during the warmest months. 3. These and other data on the determinants of blood consumption by T. infestans, were incorporated into a detailed hypothesis of density regulation in this species.     

Triatoma infestans in Greater Buenos Aires, Argentina

The Health Administration Agencies of many municipalities in Greater Buenos Aires (GBA) receive frequent reports on triatomines in houses. The aim of this work was to identify and describe the dispersal foci of Triatoma infestans in an urban neighborhood of GBA, and contribute to the knowledge of the epidemiological situation in the region. In June 1998, potentially infested places were entomologically evaluated. T. infestans was only detected in a hen building for egg production, which housed approximately 6,000 birds. A total of 2,930 insects were collected. Density was about 9 triatomines/m(2). The proportions of fifth instar nymphs and adults were significantly higher than those of the other stages (p<0.001). The number of triatomines collected largely exceeded the highest domestic infestation found in one house from rural endemic areas of Argentina. Though triatomines were negative for Trypanosoma cruzi, they could acquire the parasite by coming in contact with infected people living in GBA. Besides, the numerous and widely distributed places housing hens and chickens, would favor the settlement of the vector. Together, both facts may constitute a risk of parasitic vectorial transmission. It is recommended to intensify systematic activities of vector search and case detection in GBA.     

Mitochondrial 16S DNA variation in populations of Triatoma infestans from Argentina

Abstract.  Variation in the mtDNA 16S ribosomal RNA gene in populations of Triatoma infestans (Klug) was surveyed. DNA sequence comparisons yielded 18 haplotypes among 130 individuals from 16 localities that represent a large proportion of the range of T. infestans in Argentina. The most common genotype in all populations was found in 76.9% of individuals and two other haplotypes were shared among different populations. The remaining 15 haplotypes were present exclusively in one of the populations, suggesting currently low levels of genetic exchange. Analysis of mtDNA 16S sequences uncovered substantial genetic variation among T. infestans populations. Haplotype and nucleotide diversities varied among populations, from 0% to 0.84% and 0% to 0.29%, respectively. It appears that this locus has a low mutation rate. Uncorrected pairwise differences of T. infestans haplotypes ranged from 0% to 1.2%. The molecular phylogeny supported the monophyly of T. infestans haplotypes and clustered two different pairs of haplotypes with a moderate degree of bootstrap support (∼ 60%). Mitochondrial DNA phylogeographic differentiation was not evident, suggesting a recent rapid spread of the species. Analysis of molecular variance showed hierarchical structure in the data. Considerably less variation was found among T. infestans populations from the northwest and northeast regions than among those belonging to the central area. Such a lack of variation may be indicative of one or more past population bottlenecks.     

Spatial pattern of reinfestation by Triatoma infestans in Chancanif, Argentina.

We examined the environmental correlates and the spatial pattern of infestation by Triatoma infestans, a vector of Chagas disease, in a rural area of Argentina five years following an insecticidal campaign. Patterns of infestation were identified in an entomological survey, as mapped with high-resolution satellite imagery and analyzed in a geographic information system. Logistic regression was used to relate infestation to observed household characteristics as well as the location and density of households. Location was the most significant predictor of infestation for domiciles. For peridomestic structures surrounding the domiciles, the combination of location and the presence/absence of goat pens was most significant. In considering any infestation, whether domiciliary or peridomestic, the combination of location, presence/absence of animal pens, and the type of household construction were found to be most significant. Using these statistical relationships to back-classify the field data resulted in accuracies between 85% and 87%. A map of infestation probability for the town of Chancaní was developed from the logistic regression.     

The effects of aposymbiosis and of an infection with Blastocrithidia triatomae (Trypanosomatidae) on the tracheal system of the reduviid bugs Rhodnius prolixus and Triatoma infestans

We have investigated the effects of the absence of symbionts and of infection with a trypanosome on the tracheal supply to different organs in larvae of the blood-sucking bugs, Rhodnius prolixus and Triatoma infestans. In bugs grown without symbionts there were extensive reductions in the tracheal supply to all the internal organs examined. These bugs also excreted less fluid after blood meals, perhaps because of a reduction in the oxygen supply to the Malpighian tubules. Inclusion of vitamin B in the diet of these affected insects reversed both the adverse effects on diuresis and on the extent of the respiratory supply to the different internal organs. The results of these studies suggest that vitamin B may play a key role in the development and maintenance of an adequate tracheal supply to the tissues in these insects. Infection with the trypanosome Blastocrithidia triatomae also greatly reduced the density of tracheoles supplying the rectum, small intestine and Malpighian tubules in infected T. infestans, but not in R. prolixus. It is possible, therefore, that the parasite exerts at least part of its pathogenic effect by causing a vitamin B deficiency, that in turn affects oxygen supply to the tissues.     

Molecular phylogeography of the Chagas' disease vector Triatoma infestans in Argentina

Triatoma infestans is the main vector of Chagas' disease in South America between latitudes 10°S and 46°S. A multilocus microsatellite data set of 836 individuals from 27 populations of T. infestans, from all its range of distribution in Argentina, was analyzed. Our results favor the hypothesis of two independent migration events of colonization in Argentina and secondary contacts. The majority of the populations of the western provinces of Catamarca, La Rioja, San Juan and the west of Cordoba province, had almost no shared ancestry with the rest of the populations analyzed. Probably those populations, belonging to localities close to the Andean region, could have been established by the dispersal line of T. infestans that would have arrived to Argentina through the Andes, whereas most of the rest of the populations analyzed may have derived from the dispersal line of T. infestans in non-Andean lowlands. Among them, those from the provinces of Formosa, Chaco, Santiago del Estero and Santa Fe shared different percentages of ancestry and presented lower degree of genetic differentiation. The migratory movement linked to regional economies and possibly associated with passive dispersal, would allow a higher genetic exchange among these populations of T. infestans. This study, using microsatellite markers, provides a new approach for evaluating the validity of the different hypotheses concerning the evolutionary history of this species. Two major lineages of T. infestans, an Andean and non-Andean, are suggested.     

Dispersive flight by Triatoma infestans under natural climatic conditions in Argentina

Male and female T. infestans were released on two consecutive nights in the salinas of Cordoba Province, Argentina, when air temperatures during the flying period averaged 28.5 degrees C. 136 males (43% of the total released) and 170 females (57%) flew on the first night, and 6 males (18%) and 7 females (27%) on the second. Of these, we recovered 23 males and 14 females within 100 m, and a further female within 200 m, all from the first night's release. The remainder appear to have flown more than 100 m and possibly more than 200 m. In support of this conclusion 4 male and 5 female bugs were recovered in an abandoned brick house 550 m from the release point. Since the proportion of bugs apparently flying more than 200 m is considerably greater than that deduced from previous experiments at lower temperatures (Lehane & Schofield, 1981) it is possible that temperature influences not only the proportion of bugs flying but also the distance flown. Flight appears to be affected by wind speed. On the first night, when there was negligible wind, 43% of male and 57% of female bugs flew. On the second night, with winds gusting at 4-5 m/s, only 18% of the male and 27% of the female bugs flew.     

Distribution and pathogenicity of Trypanosoma cruzi isolated from peridomestic populations of Triatoma infestans and Triatoma guasayana from rural Western Argentina

We assessed the distribution of Trypanosoma cruzi infection in peridomestic triatomines collected manually at a district-wide scale in rural villages around Olta, Western Argentina, and typed the isolated strains according to their pathogenicity to laboratory mice. Of 1623 triatomines examined, only 14 (0.9%) were infected with T. cruzi based on microscopical examination of feces. The prevalence of T. cruzi infection was 0.8% in Triatoma infestans, 2.3% in T. guasayana, and nil in T. garciabesi, T. platensis, and T. eratyrusiformis. Local transmission occurred in kitchens, store-rooms and goat corrals or nearby, though at very low levels. T. cruzi was detected by at least one parasitological method in 11 (79%) of 14 microscope-positive bugs. Hemoculture was the most sensitive method (67%) followed by culture of organ homogenates, histopathology or xenodiagnosis of inoculated suckling mice (55-58%), and culture of microscope-positive bug feces (46%). The evidence suggests that most of the isolated T. cruzi strains would be myotropic type III. Our study establishes for the first time that peridomestic, microscope-positive T. guasayana nymphs were actually infected with T. cruzi, and may be implicated as a putative secondary vector of T. cruzi in domestic or peridomestic sites.     

Experimental Infection of Triatoma infestans and Rhodnius prolixus with Trypanosomatidae of the Genera Crithidia and Blastocrithidia*

SYNOPSIS. Dissections of Triatoma infestans and Rhodnius prolixus at various intervals after experimental infection with insect Trypanosomatidae of the genera Blastocrithidia and Crithidia (B. euschisti, C. luciliae, C. acanthocephali and C. mellificae) disclosed the protozoa to be surviving and in most instances undergoing reproduction in the experimental bugs for as long as 2 months following infection. Epimastigotes and amastigotes were seen in bugs infected with B. euschisti and choanomastigotes and amastigotes were observed in insects experimentally infected with the Crithidia. Since C. acanthocephali and C. luciliae were from clones, this is the 1st finding of these 2 structural types in this genus using cultures originating from a single choanomastigote. In view of the loose host specificity of the insect Trypanosomatidae as further emphasized by this work, it would appear that the necessity is increased for field workers in trypanosomiasis and leishmaniasis areas of the world to become well acquainted with the infective potentialities of the insect trypanosomatids of their areas for the vectors of Trypanosoma and Leishmania along with the possible association in nature of these vectors with insects which might harbor insect-limited Trypanosomatidae.     

Pathological effects of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bugs Triatoma sordida, T. pallidipennis and Dipetalogaster maxima after coprophagic infection

ABSTRACT. Developmental time and mortality in nymphs of the reduviid bugs Triatoma sordida (Stål), Triatoma pallidipennis (Stål) and Dipetalogaster maxima (Uhler) were studied in uninfected groups and in those infected with Blastocrithidia triatomae Cerisola et al. (Trypanosomatidae). In T. sordida and T. pallidipennis, major vectors of Chagas' disease in Brazil and Mexico respectively, infection with B. triatomae was associated with slight developmental retardations in the final instars, and increased mortality in the pre-adult instar. These effects were less evident in T. pallidipennis, but in this species a total infection rate of only 5–15% was achieved, compared with about 45% in T. sordida. In contrast, D. maxima was strongly affected by B. triatomae: nymphal development was retarded and complete mortality occurred in some groups exposed to infection, although not all bugs were infected.