Cannibalism and coprophagy are modes of transmission of Blastocrithidia triatomae (Trypanosomatidae) between triatomines

Transovarial transmission was not detectable among Blastocrithidia triatomae-infected Triatoma infestans. Rather, B. triatomae was transmitted directly between triatomines by cannibalism and coprophagy. Cannibalism conditions that excluded coprophagy always resulted in an infection of Dipetalogaster maxima. The efficiency of transmission was not influenced by the blood source--mice or chickens--fed to the infected donor bugs although chicken blood lyses the epimastigotes of the stomach population. Triatoma infestans was infected by coprophagy only if fed, not if unfed. Blastocrithidia triatomae in dry feces was taken up only if the feces were redissolved in fresh feces. Infections also appeared in groups of bugs fed on chickens previously used for feeding infected bugs.     

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.     

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.     

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.     

Development of symbionts in triatomine bugs and the effects of infections with trypanosomatids

In the intestinal tract of fifth instars of the hematophagous reduviid bugs Rhodnius prolixus and Triatoma infestans blood ingestion induced an initial decrease of the concentration of the respective symbiotic bacteria Rhodococcus rhodnii and Nocardia sp. and then within 10 days a 15- or 18-fold increase of the total population/bug to about 0.8 x 10(9) colony-forming units in R. prolixus and 1.8 x 10(9) colony-forming units in T. infestans. About 95-99% of the total populations of both symbionts developed in the anterior midgut regions, i.e., cardia and stomach. The passage from the blood-storing stomach to the digesting small intestine caused a considerable breakdown of symbiont populations, and only about 0.01% of the total population was present in the rectum. These were excreted mainly within 4 h after a blood meal. After infection with three species of trypanosomatids, R. rhodnii, the symbiont of R. prolixus, was affected by Trypanosoma rangeli, but not by Blastocrithidia triatomae or Trypanosoma cruzi. On the other hand, in T. infestans the concentration of Nocardia sp. was reduced after infection with B. triatomae, but not by T. rangeli nor T. cruzi. In long-term B. triatomae-infected T. infestans, this reduction and a reduced diuretic activity after feeding synergistically lowered the symbiont concentration in the singly deposited feces/urine drops drastically compared to uninfected controls. These data strongly support the theory of the mechanisms of pathogenicity of T. rangeli and B. triatomae for R. prolixus and T. infestans, respectively, that the primal point of attack is the host-specific symbiont, R. rhodnii and Nocardia sp., respectively.     

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 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.     

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.     

Effects of non-susceptible hosts on the infection with Trypanosoma cruzi of the vector Triatoma infestans: an experimental model.

We tested experimentally the effects of the presence of non-susceptible hosts on the infection with Trypanosoma cruzi of the vector Triatoma infestans. The experiment consisted in two treatments: with chickens, including two chickens (non-susceptible hosts) and two infected guinea pigs (susceptible hosts), and without chickens, including only two infected guinea pigs. The hosts were held unrestrained in individual metal cages inside a closed tulle chamber. A total of 200 uninfected T. infestans third instar nymphs were liberated in each replica, collected on day 14, and examined for infection and blood meal sources on day 32-36. The additional presence of chickens relative to infected guinea pigs: (a) significantly modified the spatial distribution of bugs; (b) increased significantly the likelihoods of having a detectable blood meal on any host and molting to the next instar; (c) did not affect the bugs' probability of death by predation; and (d) decreased significantly the overall percentage of T. infestans infected with T. cruzi. The bugs collected from inside or close to the guinea pigs' cages showed a higher infection rate (71-88%) than those collected from the chickens' cages (22-32%). Mixed blood meals on chickens and guinea pigs were detected in 12-21% of bugs. Although the presence of chickens would decrease the overall percentage of infected bugs in short term experiments, the high rate of host change of T. infestans would make this difference fade out if longer exposure times had been provided.     

The activity of nifluridide on reduviids and rodent and human trypanosomes

The ability of nifluridide to kill reduviids was assayed in mice fed 7 ppm in diet and on cattle injected subcutaneously at 5 mg/kg body weight. Nifluridide was systemically active against Triatoma infestans on mice and Rhodnius prolixus on cattle. No effects on Trypanosoma (Schizotrypanum) cruzi could be detected in the intestinal contents of Triatoma infestans killed by the compound. In vitro and in vivo studies were conducted to determine the effects of nifluridide on trypanosomes growing in medium and in experimentally infected mice. Culture forms of Trypanosoma cruzi grown at 27 degrees C that are morphologically similar to epimastigotes found in infected bugs were affected by 2.5 to 10 ppm in the medium. Mice fed nifluridide in the diet simultaneous with infection of Trypanosoma cruzi or Trypanosoma (Herpetosoma) musculi exhibited parasitemias and tissue infections similar to nontreated infected mice. At the concentration tested, bloodstream trypomastigotes and culture epimastigotes of Trypanosoma musculi were unaffected by nifluridide. Only the culture epimastigotes of Trypanosoma cruzi were affected by the drug but not the bloodstream and tissue forms.     

The peculiarities of Blastocrithidia triatomae

Blastocrithidia triatomae parasitizes triatomine bugs, the vectors of Chagas disease. Co-cultivation with a host-derived cell line permits continuous culture but the host cells are destroyed. Removal of the reduviid cells induces the formation of drought-resistant cysts, but the factors that induce encystment are unknown. Excystment is triggered after the onset of blood digestion in the insect host, a transition that is associated with unusual ultrastructural alterations. Günter Schaub, Dagmar Reduth and Mary Pudney believe that B. triatomae is a good candidate for the biological control of Chagas disease, not least because of its capacity to form highly resistant cysts in vitro.     

Trypanosoma cruzi: origin of metacyclic trypomastigotes in the urine of the vector Triatoma infestans

Population density and percentage of the different stages of an established infection of Trypanosoma cruzi were determined for two parts of the excretory system and for the rectum of fifth instars of Triatoma infestans unfed and 4 hr after feeding. These data were also evaluated for feces and urine of the fed bugs. In the first unfed group only small populations of the flagellate occurred in the Malpighian tubules and ampullae and not in all bugs. The three rectal populations (rectal lumen and anterior and posterior rectal wall) consisted of approximately equal numbers. About 10% were spheromastigotes and about 10% were stages intermediate to epimastigotes. Significantly fewer epimastigotes and more trypomastigotes were present on the rectal wall than in the lumen. Two intermediate forms leading to the trypomastigote stage occurred in similar numbers. In nearly all bugs the initial excretion (feces) contained the highest number of flagellates as compared to the following drops of urine. More flagellates were excreted through the urine than were contained in the excretory system of unfed bugs. The population in the feces reflected the percentage of forms present in the rectal lumen of unfed bugs, but in the urine the percentage of trypomastigotes increased up to 100%. Four hours after blood uptake, dissection of bugs still showed parasites in the Malpighian tubules and ampullae; the total number of parasites in the rectum was reduced by more than 50%. This reduction was more pronounced in the rectal lumen and on the posterior rectal wall. In stained smears from all three rectal populations there were rarely spheromastigotes but high percentages of epimastigotes. The intermediate stages leading to trypomastigotes mainly originated from short epimastigotes. Comparison of the T. cruzi populations before and after feeding demonstrates that the trypomastigotes in the urine should originate from the rectal wall, especially from the posterior part.     

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.     

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.     

Does Trypanosoma cruzi stress its vectors?

Trypanosoma cruzi seems to compete with its vector, Triatoma infestans, for nutrients. When starved the resistance of infected Triatoma is reduced but it is rarely affected i f it is given an adequate food supply. Infected individuals also might be more sensitive than uninfected bugs to other environmental stress factors. Günter Schaub believes that the theory, that T. cruzi does not affect its vectors, should be re-examined.     

Triatomines involved in domestic and wild Trypanosoma cruzi transmission in Concepción, Corrientes, Argentina

An entomological and serological survey was performed in three localities of the Department of Concepción, Province of Corrientes, Argentina in 1998 and 1999, to identify triatomines species involved in domestic and wild transmission of Chagas disease. Triatomines were collected by man/hour capture in 32 houses randomly selected and 44 nearby outdoor ecotopes. Trypanosoma cruzi infection in triatomines was assessed by direct microscopic observation (400x) of feces and polymerase chain reaction. Serological techniques used for people were Indirect Hemagglutination Test and Indirect Fluorescent Test. Triatomines were collected in 28.1% of the houses and 31.8% of the wild biotopes. Triatoma infestans (Klug 1834) was exclusively found indoors and T. cruzi infected 60% of them. Triatoma sordida (St?l 1859) was mainly found in extradomestic ecotopes where trypanosome infection rate reached 12.7%. Serological study of 98 local people showed that 29.6% were seroreactive; most of their houses were closed to wild biotopes colonized by T. sordida. Results indicate that there is an active T. infestans mediated transmission of Chagas disease in this zone that yields important human prevalence and that the populations of T. sordida in wild biotopes not only sustain the wild T. cruzi cycle but also represent an actual risk for people living in the area.     

Identification of trypanosomes isolated from reduviidae from north Chile

Examination of 54 Triatoma infestans from a village near the European Southern Observatory La Silla in Chile and of 9 Triatoma spinolai from the territory of the observatory showed that 10 T. infestans were infected with trypanosomatids. Mice were infected with in vitro cultures initiated with five different trypanosomatid isolates and treated with the immunosuppressive drug cyclophosphamide to increase the parasitemia of the flagellates. Evidence of the presence of T. cruzi was provided by a comparative biometrical analysis of blood trypomastigotes and the occurrence of intracellular amastigotes. Three methods for further identification were used: examination of kDNA ultrastructure, disc electrophoresis of soluble proteins and the Aaptos papillata II lectin induced agglutination. We obtained the following results for all isolates: (1) presence of a central band of the kDNA; (2) T. cruzi specific double bands of the protein patterns; (3) positive reaction with Aaptos papillata II. No differences between the five isolates from Chile and T. cruzi or T. cruzi-like strains from other countries could be observed. Based on these results an infection of the bugs with T. rangeli and T. conorhini could be excluded.     

Effects of chickens on the prevalence of infestation and population density of Triatoma infestans in rural houses of north-west Argentina

Abstract Effects of the presence of chickens on population density of the bug Triatoma infestans , principal vector of Chagas disease, were investigated by standardized sampling (indoors and peridomestically) from sixty-eight houses of three rural communities in north-west Argentina, during March 1992.
The domiciliary density of T. infestans increased linearly with the percentage of bugs that fed on chickens, as identified by agar double-diffusion tests. Bug density was significantly higher in houses where hens usually nested indoors than in those where they did not, as determined by concurrent direct observations and interviews of householders. Multiple linear regression analysis of domiciliary bug density on (a) the total number of people, dogs and cats per house; (b) the percentage of domiciliary bugs that fed on chickens, or (c) the indoor-brooding habit of hens, showed the two variables (b, c) related to chickens as significant predictors in each regression model. Inclusion both variables representing chickens increased the fit significantly. Addition of other potentially confounding factors (domestic insecticide use, type of roof and walls of house) did not affect the significant variables retained in the best-fitting regression model.
Peridomestic infestation was positively associated with the household number of fowls. Chickens were the main bloodmeal source of peridomestic T.infestans populations. Human-fed bugs were detected in peridomestic sites of sixteen houses, indicating active dispersal of adults and large nymphal instars from bedroom areas.
Exclusion of hens from domiciliary areas and promotion of chicken sheds, of an appropriate design that would not harbour bug populations, should limit the triatomine population growth rate and reduce the risk of infestation.     

Temporal change of the aggregation response in Triatoma infestans

Adults and larvae of Triatoma infestans spend daylight hours assembled in shaded places. An assembling factor has been demonstrated in the excrement of this species. We analysed different aspects of the dynamics of the response of bugs. Recently fed insects do not aggregate around faeces. They start to show a significant assembling response from the 8th hour after feeding onwards. Just deposited faeces do not evoke assembling, but a significant rejection instead. This reaction switches 3 h after deposition, when the faeces become attractive to the insects. The attractiveness of faeces persists for about 10 days and can be recovered after this time by rehydration. These findings are discussed in relation to the biological role of faeces and the dynamics of the use of refuges by T. infestans.     

The role of water vapour in the orientation behaviour of the blood-sucking bug Triatoma infestans (Hemiptera,Reduviidae)

The behavioural response to water vapour of the haematophagous bug Triatoma infestans was analysed. Dry or humid discrete sources at different temperatures were used as stimuli for insects walking on a locomotion compensator. Humidity significantly increased the tendency of these bugs to orientate towards thermal sources. Furthermore, humid sources at room temperature were attractive to T. infestans, but this effect was limited to short-range distances. On the other hand, dynamic sources, i.e. airstreams carrying different water vapour contents did not affect the spontaneous anemotactic behaviour of this species, neither in sign (positive) nor in intensity. The anemotactic behaviour was also not influenced by the physiological water balance state of the bugs. Results are discussed in relation to the cues released by living hosts of triatomine bugs and in relation to their responses to air-currents.