Coinfection by Trypanosoma cruzi and a fungal pathogen increases survival of Chagasic bugs: advice against a fungal control strategy

Triatomine bugs carry the parasitic protozoa Trypanosoma cruzi, the causal agent of Chagas disease. It is known that both the parasite and entomopathogenic fungi can decrease bug survival, but the combined effect of both pathogens is not known, which is relevant for biological control purposes. Herein, the survival of the triatomine Meccus pallidipennis (Stal, 1872) was compared when it was coinfected with the fungus Metarhizium anisopliae (Metschnikoff) and T. cruzi, and when both pathogens acted separately. The immune response of the insect was also studied, using phenoloxidase activity in the bug gut and hemolymph, to understand our survival results. Contrary to expectations, triatomine survival was higher in multiple than in single challenges, even though the immune response was lower in cases of multiple infection. We postulate that T. cruzi exerts a protective effect and/or that the insect reduced the resources allocated to defend itself against both pathogens. Based on the present results, the use of M. anisopliae as a control agent should be re-considered.

Immune defence mechanisms of triatomines against bacteria, viruses, fungi and parasites

Triatomines are vectors that transmit the protozoan haemoflagellate Trypanosoma cruzi, the causative agent of Chagas disease. The aim of the current review is to provide a synthesis of the immune mechanisms of triatomines against bacteria, viruses, fungi and parasites to provide clues for areas of further research including biological control. Regarding bacteria, the triatomine immune response includes antimicrobial peptides (AMPs) such as defensins, lysozymes, attacins and cecropins, whose sites of synthesis are principally the fat body and haemocytes. These peptides are used against pathogenic bacteria (especially during ecdysis and feeding), and also attack symbiotic bacteria. In relation to viruses, Triatoma virus is the only one known to attack and kill triatomines. Although the immune response to this virus is unknown, we hypothesize that haemocytes, phenoloxidase (PO) and nitric oxide (NO) could be activated. Different fungal species have been described in a few triatomines and some immune components against these pathogens are PO and proPO. In relation to parasites, triatomines respond with AMPs, including PO, NO and lectin. In the case of T. cruzi this may be effective, but Trypanosoma rangeli seems to evade and suppress PO response. Although it is clear that three parasite-killing processes are used by triatomines - phagocytosis, nodule formation and encapsulation - the precise immune mechanisms of triatomines against invading agents, including trypanosomes, are as yet unknown. The signalling processes used in triatomine immune response are IMD, Toll and Jak-STAT. Based on the information compiled, we propose some lines of research that include strategic approaches of biological control.

Immunogenic salivary proteins of Triatoma infestans: development of a recombinant antigen for the detection of low-level infestation of triatomines

BACKGROUND

Triatomines are vectors of Trypanosoma cruzi, the etiological agent of Chagas disease in Latin America. The most effective vector, Triatoma infestans, has been controlled successfully in much of Latin America using insecticide spraying. Though rarely undertaken, surveillance programs are necessary in order to identify new infestations and estimate the intensity of triatomine bug infestations in domestic and peridomestic habitats. Since hosts exposed to triatomines develop immune responses to salivary antigens, these responses can be evaluated for their usefulness as epidemiological markers to detect infestations of T. infestans.

METHODOLOGY/PRINCIPAL FINDINGS

T. infestans salivary proteins were separated by 2D-gel electrophoresis and tested for their immunogenicity by Western blotting using sera from chickens and guinea pigs experimentally exposed to T. infestans. From five highly immunogenic protein spots, eight salivary proteins were identified by nano liquid chromatography-electrospray ionization-tandem mass spectrometry (nanoLC-ESI-MS/MS) and comparison to the protein sequences of the National Center for Biotechnology Information (NCBI) database and expressed sequence tags of a unidirectionally cloned salivary gland cDNA library from T. infestans combined with the NCBI yeast protein sub-database. The 14.6 kDa salivary protein [gi|149689094] was produced as recombinant protein (rTiSP14.6) in a mammalian cell expression system and recognized by all animal sera. The specificity of rTiSP14.6 was confirmed by the lack of reactivity to anti-mosquito and anti-sand fly saliva antibodies. However, rTiSP14.6 was recognized by sera from chickens exposed to four other triatomine species, Triatoma brasiliensis, T. sordida, Rhodnius prolixus, and Panstrongylus megistus and by sera of chickens from an endemic area of T. infestans and Chagas disease in Bolivia.

CONCLUSIONS/SIGNIFICANCE

The recombinant rTiSP14.6 is a suitable and promising epidemiological marker for detecting the presence of small numbers of different species of triatomines and could be developed for use as a new tool in surveillance programs, especially to corroborate vector elimination in Chagas disease vector control campaigns.

Susceptibility of different triatomine species to Trypanosoma rangeli experimental infection

Trypanosoma rangeli is a kinetoplastid protozoan parasite that has been found in the majority of Latin American countries, overlapping its distribution area with that of Trypanosoma cruzi, the causative agent of Chagas disease. This parasite shares the same reservoirs and vectors as T. cruzi. Triatomines from genus Rhodnius are considered the most susceptible hosts to infection. In this work, we report the susceptibility of different triatomine species (Rhodnius neglectus, Panstrongylus megistus, Triatoma infestans, T. sordida, T. braziliensis, and T. vitticeps) to experimental infection by T. rangeli isolated from Didelphis albiventris in a highly endemic region for Chagas disease. An intense parasitism was evidenced in feces (56% to 81%) of the majority of the species studied on the 10th day after infection, decreasing during the period of the experiment (30 days). T. vitticeps did not present parasites in feces at any time. All triatomine species presented parasites in the hemolymph. In T. vitticeps and P. megistus, this parasitism was scarce (6.3% and 6.6%, respectively). In the other species, the parasitism was variable (62.5% to 100%). Triatomine mortality varied between 3% to 40%, increasing during the infection in all species studied. The lowest mortality was observed for T. infestans. Also, we showed that only trypomastigotes forms from salivary glands, and hemolymph were infective for mice. We conclude that all triatomine species used were susceptible to infection by T. rangeli at different levels. There was no direct correlation between intensity of parasitism and mortality.

Human immune response to triatomine embryo extract

Dipetalogaster maximus embryo extracts were used to stimulate peripheral blood mononuclear cells (PBMC) and in ELISA with sera either from Trypanosoma cruzi infected or non-infected individuals. The results showed that there was significant proliferative response and high antibody, titers in sera of chagasic patients.

Trypanosoma cruzi strain-specific monoclonal antibodies: identification of Colombian strain flagellates in the insect vector

Spleen cells from mice immunized with insect-derived Trypanosoma cruzi metacyclic trypomastigotes were used to obtain Colombian strain-specific monoclonal antibodies. At least 4 different strain-specific antigens were recognized by the monoclonal antibodies on epimastigotes or metacyclic trypomastigotes. There was no reactivity with other stages of Colombian strain T. cruzi, nor with any stage of 15 other T. cruzi strains or isolates, nor with 22 other Trypanosomatidae. One of the monoclonal antibodies was used to identify, by indirect immunofluorescence, Colombian strain flagellates in cryostat sections or glass-slide smears of the insect vector's intestine.

Identification and partial purification of species-specific allergens from Triatoma protracta (Heteroptera:Reduviidae)

This article describes the immunochemical characterization of allergens from Triatoma protracta, a hematophagous insect that causes IgE-mediated anaphylactic reactions when it bites sensitized allergic persons. Comparison of the allergenic potency of T. protracta salivary gland extract, thoracic and abdominal hemolymph, and a whole body extract by RAST inhibition demonstrated that salivary glands were the main source of T. protracta allergens. Concentrated salivary gland extracts were purified by gel filtration and isoelectric focusing. Fractions were tested for allergenic activity by RAST inhibition and for protein purity by polyacrylamide gel electrophoresis and immunoelectrophoresis. Two protein peaks were obtained on gel filtration. The high-molecular-weight peak contained a 70,000 MW protein/glycoprotein that had little allergenic activity. The low-molecular-weight peak comprised six proteins, molecular weight 17,000 to 25,000, and T. protracta allergen(s) eluted in parallel with this peak. These proteins were resolved by isoelectric focusing, and two fractions, pI 6.7 to 7.3 and pI 8.2, contained most of the allergenic activity. By RAST, 25/28 sera from T. protracta-allergic patients contained IgE antibody to these fractions, suggesting that they were major allergens. Each fraction demonstrated a single precipitin arc on immunoelectrophoresis and two bands, molecular weight 18,000 to 20,000, on gel electrophoresis. Cross-inhibition radioimmunoassays demonstrated that each fraction completely inhibited binding of the other fraction to IgE antibody, suggesting that they contained different isoelectric forms of the same allergen.

Species-specific allergens from the salivary glands of Triatominae (Heteroptera:Reduviidae)

We investigated allergenic cross-reactivity among species of the blood-feeding insects of the subfamily Triatominae. By skin testing, patients allergic to either Triatoma protracta or T. rubida gave positive responses only to the respective salivary antigen. RAST-inhibition experiments demonstrated that binding of IgE antibodies to T. protracta antigen was not inhibited by salivary extracts from T. rubida, T. cavernicola, T. rubrofasciata, or Rhodnius prolixus. The same level of species specificity was found for IgE antibodies to T. rubida. By direct RAST, no T. rubida positive serum bound T. protracta antigen, and 29 of 30 T. protracta positive sera failed to bind T. rubida. One serum from a T. protracta-allergic patient contained IgE antibodies to both T. protracta and T. rubida. RAST-inhibition experiments demonstrated that these antibodies did not cross-react and that this person had separate species-specific antibodies to T. protracta and T. rubida antigens. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of salivary extracts demonstrated that the lower molecular weight bands that contain the antigens responsible for human allergic reactions differed in number and size in all species tested. These studies demonstrate species specificity for the allergic response to Triatoma and stress the importance of accurate insect identification and the need for species-specific antigens for diagnosis and immunotherapy.

Studies of kissing bug-sensitive patients: evidence for the lack of cross-reactivity between Triatoma protracta and Triatoma rubida salivary gland extracts

In the southern and western sections of the United States, bites from the reduviid bug, commonly known as the kissing bug, genus Triatoma, may induce serious life-threatening allergic reactions. This study was undertaken to identify the allergens responsible for patient sensitization and to determine the extent of cross-reactivity of these allergens. The Triatoma spp. most commonly encountered in California and Arizona, T. protracta and T. rubida, were obtained, maintained in the laboratory, and dissected to prepare extracts for testing. Extracts were prepared from T. protracta and T. rubida for study by RAST, lymphocyte transformation, leukocyte histamine release, and RAST inhibition. Sera and cells were collected from patients who had generalized reactions to Triatoma bites. Our results indicate that T. protracta and T. rubida antigens to which patients are sensitized are present in extracts that contain saliva and that human responses are specific for T. protracta or T. rubida, i.e., allergic cross-reactivity could not be demonstrated.

Successful immunotherapy for Triatoma protracta-induced anaphylaxis

A successful program of immunotherapy for Triatoma protracta-induced anaphylaxis was developed. This program included a new passive extract-antigen preparation standardized by RAST inhibition. This antigen facilitated the development of a reliable skin test protocol for in vivo diagnosis of Triatoma protracta allergy. Five patients with T. protracta-induced anaphylaxis underwent a rapidly increasing dosage schedule of immunotherapy. The IgE- and IgG-antibody responses during immunotherapy were followed with solid-phase RIA. Protection against anaphylaxis was confirmed in all patients with a "bite challenge" by T. protracta. This is the first report of completely successful T. protracta immunotherapy.

Cutaneous allergic reactions to Triatoma infestans after xenodiagnosis

We determined the frequency of cutaneous allergic reactions to bites of Triatoma infestans during xenodiagnosis in a rural community where Panstrongylus megistrus is the only domestic vector of Trypanosoma cruzi. Localized urticaria or more intense cutaneous allergic reactions at 48 and 72 hours were observed in 86.7% and 82.1% respectively of the individuals in our study. Urticaria was more severe in children and older adults and in women than in men. The high frequency of reactions suggests either cutaneous reactivity to T. infestans without prior sensitization or cross reactivity between P. megistus and T. infestans. A single application of topical corticosteroid or antihistamine medication did not reduce the cutaneous reactions.

[Evidence of hepatitis B antigen (HBsAg) in Triatominae]

De 3.200 "manchas" provenientes de insetos dos gêneros Triatoma e Panstrogylus, positivas para sangue humano, 12 deram resultados presuntivamente positivos, por imunodifusão, para HBsAg. Deste total, só 7 casos foram confirmados como positivos, por radioimunoensaio, correspondendo todos eles a "manchas" obtidas de ninfas de Triatoma infestans.