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Biomedical subjects

P Azambuja

Publications and source records attributed to P Azambuja.

At least 37 records · Page 2Linked to original sources
PubMed1997

Immune responses in Rhodnius prolixus: influence of nutrition and ecdysone.

Starved larvae of Rhodnius prolixus, when challenged with Enterobacter cloacae B12, had their mortality related to their period of starvation. R. prolixus larvae fed on plasma alone, compared with insects fed on whole blood, had their immune reactivity affected as shown by: (i) a significant reduction in the ability to produce cecropin-like and lysozyme activities in the haemolymph when inoculated with E. cloacae; (ii) a reduction in numbers of haemocytes and nodule formation following challenge with bacteria; (iii) a decreased ability of plasma-fed insects in destroying their infection caused by inoculation of E. cloacae cells; and (iv) alpha-ecdysone therapy counteracted the immune depression in Rhodnius larvae fed on plasma alone. However, unlike other immune reactions, this set of experiments failed to demonstrate any interference of the plasma feeding on the prophenoloxidase-activating system, since melanin production was not reduced when the system was stimulated by the presence of bacteria in the haemolymph. The significance of these data is discussed in relation to the effect of diet components and the moulting hormone on the immune reactivity in insects.

Journal Article↗
PubMed1997

Biological effects of canatoxin in different insect models: evidence for a proteolytic activation of the toxin by insect cathepsinlike enzymes.

Canatoxin is a toxic protein isolated from the jackbean, Canavalia ensiformis. The toxin injected intraperitoneally is lethal for mice and rats; however, it is inactive if given orally. In this study, Manduca sexta (L.) (Lepidoptera), Schistocerca americana (Drury) (Orthoptera), Drosophila melanogaster (L.) (Diptera), Aedes aegypti (L.) (Diptera), Rhodnius prolixus (Stål) (Hemiptera), and Callosobruchus maculatus (F.) (Coleoptera) were fed on canatoxin-containing diets. No effects were seen in M. sexta, S. americana, D. melanogaster, or A. aegypti. No traces of canatoxin were found in their feces, suggesting that the protein was digested completely by these insects, which characteristically have a trypsin-based digestion. In contrast, canatoxin was lethal for insects displaying cathepsin-based digestion. Thus, for C. maculatus, a diet containing 0.25% wt:wt canatoxin caused complete inhibition of larval growth. When R. prolixus were fed on canatoxin, 2 effects were seen: impairment of water excretion and increased lethality 48-96 h after feeding. The lethal effect of canatoxin in R. prolixus was blocked partially or completely when the digestion of the toxin by R. prolixus midgut enzymes was impaired. The data showed that canatoxin is highly toxic when ingested by some species of insects but not affecting others, probably in correlation with the characteristics of the digestive process of the insect.

Aedes↗
PubMed1996

Differential in vitro and in vivo behavior of three strains of Trypanosoma cruzi in the gut and hemolymph of Rhodnius prolixus.

A comparison was made of the agglutination and lysis of three strains of Trypanosoma cruzi in gut extracts and hemolymph of Rhodnius prolixus and the results obtained were correlated with the success or failure of the parasite strain to infect the digestive tube or to survive in the hemocel after inoculation. Both T. cruzi strains Dm28c and Cl urine 35 days after feeding with parasites. Concomitantly, both of these strains were agglutinated but not lysed by the crop extracts. In contrast, T. cruzi Y strain parasites rapidly disappeared from the gut and showed no agglutination, but some lysis, in the crop extract. Following inoculation into the hemocel, only the Cl strain survived at high levels and was also the only strain agglutinated significantly in the hemolymph. Both Dm28c and Y strains rapidly disappeared from the hemocel with the former parasite being removed more slowly than the latter, probably due to clearance by the cellular defenses. The rapid clearance of the Y strain was correlated with the presence of a high titer lysin in the hemolymph. Subsequent experiments using FITC-labeled lectins and FACS to probe the carbohydrates on the parasite surfaces showed significant differences between the three strains. Thus, only Dm28c was stained strongly by Arachis hypogea (PNA) lectin, indicating the presence of galactose/N-acetylgalactosamine residues, and Dm28c and Y strains by Phytolacca lectin for N-acetyl glucosamine moieties. Finally, the fact that, in contrast to Dm28c and Y, the Cl strain strongly interacted with Triticum vulgaris (WGA) but not with Phytolacca lectin may be due to the presence of N-acetyl neuraminic acid residues on these organisms. These surface carbohydrate differences may be correlated both to the behavior and agglutination variations between the three strains recorded in this work.

Agglutination Tests↗
PubMed1996

Trypanosoma cruzi and erythrocyte agglutinins: a comparative study of occurrence and properties in the gut and hemolymph of Rhodnius prolixus.

The activity of agglutinins found in the gut tissues and hemolymph of Rhodnius prolixus was tested using rabbit erythrocytes, Trypanosoma cruzi, or Trypanosoma rangeli as test particles. In addition, investigations were made of the influence of parasitic infection and insect diet on the agglutination titers. A range of physicochemical tests and carbohydrate-binding studies were performed and inhibitors were subsequently found for both the crop agglutinin (p-nitrophenol-derived sugars) and the hemolymph agglutinin (galactose-type sugars). As a result, affinity chromatography was utilized for an attempted purification of these agglutinins, and a one-step purification protocol for the R. prolixus hemolymph agglutinin has been developed. Preliminary results of some biological and physicochemical characteristics of this pure agglutinin are described. These results represent a starting point for future studies of lectin/parasite interaction in this reduviid-trypanosome model.

Animals↗
PubMed1995

Trypanosoma cruzi and Trypanosoma rangeli: interplay with hemolymph components of Rhodnius prolixus.

Studies were carried out on the course of infection of Trypanosoma cruzi (clone Dm28c) and Trypanosoma rangeli (clone San Agustin) and their interactions with hemolymph components of Rhodnius prolixus. These parasites when inoculated into the hemocoel of adult R. prolixus (i) had different courses of infection (T. rangeli had high rates of both multiplication and infection and T. cruzi had no division and disappeared soon from the hemolymph); (ii) induced high but no differential increases in lysozyme levels; (iii) failed to induce any other antibacterial activity; (iv) showed similar patterns of hemolymph agglutination activity for erythrocytes and parasites, although there was evidence of limited, unquantifiable, agglutination of T. cruzi; (v) elicited different hemocyte responses with only the T. rangeli infection resulting in significantly increased hemocyte counts; and (vi) did not induce trypanolytic activity. These experiments, unlike previous studies, also showed (i) an interaction of these trypanosomes with the prophenoloxidase-activating system [phenoloxidase (PO) production was spontaneously activated by both parasites but the number of T. cruzi in the hemolymph was directly correlated with PO levels] and (ii) that the elimination of T. cruzi also corresponded to the formation of nodules in the hemolymph. The significance of these results is discussed in relation to the hypothesis that T. rangeli but not T. cruzi has the ability to escape from and perhaps utilize the vector immune system in order to successfully colonize the R. prolixus hemolymph.

Animals↗
PubMed1994

Rhodnius prolixus: salivary antihemostatic components decrease with Trypanosoma rangeli infection.

Feeding behavior and some antihemostatic properties of the saliva of Rhodnius prolixus infected with Trypanosoma rangeli were studied and compared with those of uninfected controls. Insects with salivary gland infection pierced host skin more often and drew less blood and at a lower rate than controls when feeding on a rabbit. None of these differences was observed when feeding was performed through a membrane feeder. Salivary gland homogenates from infected insects, at 30 days after feeding/infection, had a significantly lower amount of total protein/salivary gland pair and less anticoagulant activity than controls. Also, infected salivary glands exhibited significantly reduced apyrase activities and reactive nitrogen groups when compared to controls. It is concluded that salivary infection of T. rangeli impairs the ability of the vector to locate blood vessels by affecting salivary antihemostatic properties, thus enhancing the possibility of intradermal inoculation of parasites into the mammalian host.

Animals↗
PubMed1991

Development and interactions of Trypanosoma cruzi within the insect vector.

Transmission of Chagas disease or American trypanosomiasis depends on Trypanosoma cruzi development and differentiation within its triatomine insect vector. In this review, Eloi Garcia and Patricia de Azambuja aim to outline the current areas of research that may explain aspects of the parasite-vector interaction.

Journal Article↗
PubMed1991

Effects of azadirachtin in Rhodnius prolixus: data and hypotheses.

The effects of azadirachtin A, a tetranortriterpenoid from the neem tree Azadirachta indica J., on both development and interaction between Trypanosoma cruzi, the causative agent of Chagas' disease, and its vector Rhodnius prolixus were studied. Given through a blood meal, a dose-response relationship of azadirachtin was established using antifeedant effect and ecdysis inhibition as effective parameters. A single dose of azadirachtin A was able to block the onset of mitosis in the epidermis and ecdysteroid titers in the hemolymph, determined by radioimmuneassay, were too low for an induction of ecdysis. The survival of T. cruzi was also studied in R. prolixus treated with the drug. If the trypomastigotes were fed in presence of azadirachtin A the number of parasites drastically decreased. If the drug was applied after infection of the bug with T. cruzi, the parasite was still abolished from the gut. If the insect was pretreated with azadirachtin A before infection the same observation was obtained. A single dose of azadirachtin A was enough for a permanent resistance of the insect host against its reinfection with T. cruzi and for blocking the ecdysis for a long time. The effects of azadirachtin A on the hormonal balance of the host and growth inhibition of the parasite will be discussed on the basis of the present results.

Animals↗
PubMed1989

In vitro cytotoxicity of Rhodnius prolixus hemolytic factor and mellitin towards different trypanosomatids.

Trypanosoma cruzi strain Y and clone Dm28c and other trypanosomatids were exposed to two lytic agents, Rhodnius prolixus hemolytic factor (RHF) and mellitin, in vitro. In both cases, the result was a significant decrease in the number of parasites after a 30-min treatment at 37 degrees C. RHF and mellitin had distinct activities on different strains and species of trypanosomatids. These observations suggest that RHF may be an important factor in selecting resistant strains of trypanosomes for development in the vector's gut.

Animals↗
PubMed1987

Demonstration of a proallatotoxin-sensitive period in 4th-instar nymphs of Rhodnius prolixus.

1. Topical application of the proallatotoxin ethoxyprecocene II (60 micrograms/nymph) to 4th-instar nymphs of Rhodnius prolixus at various times before and after a blood meal induced precocious metamorphosis. 2. The highest percentage of adultoids was obtained when proallatotoxin was applied prior to feeding or up to day 3 after the blood meal. 3. The proallatotoxin-sensitive period ended 4 days after feeding just before the maximum peak of ecdysteroid concentration in the hemolymph. 4. The significance of these findings is discussed in terms of the juvenile hormone-sensitive period and the hormonal program which controls molting in this insect.

Administration, Topical↗
PubMed1987

Characterization of inducible lysozyme activity in the hemolymph of Rhodnius prolixus.

1. The characterization and partial purification of an induced lysozyme activity in the hemolymph of adult Rhodnius prolixus inoculated with Micrococcus lysodeikticus is described. 2. Little or no activity against M. lysodeikticus appeared in the first hours after inoculation, but the activity increased reaching a maximum 4 days later, which was maintained to day 12. 3. The activity was characterized as lysozyme on the basis of the following considerations: 1) pH optimum and thermostability at acidic pH; 2) rate of lysis negatively dependent on ionic strength; 3) binding to SP-Sephadex at pH 5.5; 4) apparent molecular weight of 15 kDal. 4. Crude or semi-purified enzyme preparations showed a high degree of stability during handling, freezing and thawing, and standing at 5 degrees C. 5. Incubation of abdominal fat bodies from treated insects resulted in the release of activity into the medium. 6. The relationship between induced lysozyme activity and its role as an insect defense mechanism is discussed.

Animals↗
PubMed1985

A protein diet initiates oogenesis in Rhodnius prolixus.

Oogenesis in R. prolixus females is induced by feeding blood, blood plasma, a suspension of washed erythrocytes, or 5% solutions of egg albumin, bovine serum albumin or hemoglobin. Unfed females and those fed saline, casein hydrolysate, dextran or sucrose do not initiate oogenesis. The juvenile hormone analogue epoxygeranylgeraniol methyl ester induced oogenesis in unfed females as well as in ethoxyprecocene II-treated insects. The results show that a protein meal was sufficient to initiate oogenesis. They also support the view that oogenesis depends on a relationship between protein ingestion and corpus allatum function and that oogenesis is not controlled by hormones released in response to abdominal stretching.

Animals↗
PubMedDate not supplied

Isolation of Serratia marcescens in the midgut of Rhodnius prolixus: impact on the establishment of the parasite Trypanosoma cruzi in the vector.

The effects of resident bacteria in the stomach of 5th-instar larvae of Rhodnius prolixus on the erythrocyte lysis and Trypanosoma cruzi infection were studied. The bacteria population increased approximately 10,000-fold after feeding. Hemolysis rose to approximately 28% within 24h postfeeding and then linearly grew until day 4 attaining almost 100%. The number of surviving Y strain of T. cruzi in the stomach declined drastically, while the infection with Dm28c clone was maintained stable. Five days after feeding, few different types of bacterial colonies were obtained when stomach content suspensions were spread onto BHI agar plates. The hemolytic bacteria were isolated and identified as Serratia marcescens biotype A1a (referenced as RPH), which produces the pigment prodigiosin. In vitro experiments, comparing incubations of RPH with S. marcescens SM365, a prodigiosin pigment producer, and S. marcescens DB11, a nonpigment variant, as a control, with erythrocytes and T. cruzi demonstrated that: (i) at 30 degrees C, SM365 and RPH diminished the populations of Y strain, but not DM28c clone, and DB11 was unable to lyse both T. cruzi strains; (ii) at 0 degrees C, SM263 and RPH killed the flagellates, but DB11 did not; and (iii) all three strains of S. marcescens were able to lyse erythrocytes. These results suggest that S. marcescens trypanolytic activity from the SM365 and RPH strains is distinct from the hemolytic activity and that prodigiosin is an important factor for the trypanolytic action of the bacteria.

Animals↗
PubMedDate not supplied

In vivo and in vitro metacyclogenesis tests of two strains of Trypanosoma cruzi in the triatomine vectors Triatoma pseudomaculata and Rhodnius neglectus: short/long-term and comparative study.

Metacyclogenesis of Trypanosoma cruzi of the Y and Berenice strains was studied in Triatoma pseudomaculata and Rhodnius neglectus. Results in vivo showed a higher production of metacyclic trypomastigotes in R. neglectus' digestive tube than in T. pseudomaculata. In vitro experiments were also carried out in order to compare the behavior of culture forms of T. cruzi incubated in extracts of different compartments (stomach, intestine, and rectum) of the digestive tract of both species of triatomines. A higher percentage of metacyclic trypomastigotes for both parasite strains, Y and Berenice, was detected in the rectum extract of R. neglectus in comparison to that from T. pseudomaculata. The same results were obtained with in vitro experiments, using parasites incubated in urine from each of those vectors. The adhesion of parasites to the incubated rectum epithelial cells was also compared. In incubations with the Y strain no significant differences were detected between the two triatomine species but, however, with the Berenice strain the mean percentage of cells with adhered parasites was higher in R. neglectus than in T. pseudomaculata.

Animals↗
PubMedDate not supplied

Chagas' disease and its insect vector. Effect of azadirachtin A on the interaction of a triatomine host (Rhodnius prolixus) and its parasite (Trypanosoma cruzi).

The ED50 for moulting inhibition by injected azadirachtin A is for fourth instar larvae of all the triatomines, Triatoma vitticepes, T. pseudomaculata, T. maculata, T. brasiliensis, T. lecticularis, T. matogrossensis, T. infestans, Rhodnius prolixus. R. neglectus, R. robustus, Panstrongylus megistus, and P. herrera in the range of 10-25 ng/larva. In Rhodnius prolixus, the survival of T. cruzi was studied after treatment with the drug. If the trypomastigotes were fed in presence of 1.0 microgram azadirachtin A/ml blood, the number of parasites decreased near to the limit of detection within 30 days. If the drug was applied 20 days after T. cruzi infection, it still completely abolished the parasite in the host's gut within the subsequent 20 days. The same holds true if the insect larvae were pretreated with azadirachtin A 20 days before the subsequent infection with T. cruzi. Azadirachtin A. if applied at the dose of 1 microgram/ml, did not affect the hemolytic activity of the crop contents or the proteinase content of the intestine. A parallel between azadirachtin effects on the hormone balance of the host and growth inhibition of the parasite is discussed on the basis of the present results.

Animals↗
PubMedDate not supplied

Comparative studies on the growth and reproductive performances of Rhodnius prolixus reared on different blood sources.

Host blood source was found to affect both the development and the reproductive performance of Rhodnius prolixus. The insects were reared on citrated human, rabbit, chicken, sheep and horse blood sources, through a membrane feeder, during an entire life cycle, from eggs to adults. Development and reproduction in terms of the number of unfed insects, number of moulting, mortality intermoulting period, number of egg/female, conversion of blood into egg (mg meal/egg) and percentage of hatch as effective physiological parameters were investigated. Our results showed that human or rabbit blood meals were more nutritionally efficient than the other blood samples used because (i) the insects developed faster, presented low mortality and about 80% of them reached the adult stage; and (ii) females oviposited an average of at least 100% more eggs. The inefficiency of chicken and horse blood sources as diets for R. prolixus was manifested in (i) a decrease of the amount of ingested blood and (ii) only a reasonable nutritional quality. The inadequacy of sheep blood was observed by a mortality extremely high, poor moulting response and drastic reduction in egg production.

Animals↗