Trypanosoma cruzi I genotype among isolates from patients with chronic Chagas disease followed at the Evandro Chagas National Institute of Infectious Diseases (FIOCRUZ, Brazil)

ABSTRACT

INTRODUCTION:

Trypanosoma cruzi is the etiologic agent of Chagas disease in humans, mainly in Latin America. Trypanosome stocks were isolated by hemoculture from patients followed at Evandro Chagas National Institute of Infectious Diseases (FIOCRUZ) and studied using different approaches.

METHODS:

For species and genotype identification, the stocks were analyzed by parasitological techniques, polymerase chain reaction assays targeted to specific DNA sequences, isoenzyme patterns, besides sequencing of a polymorphic locus of TcSC5D gene (one stock).

RESULTS:

The isolates presented typical T. cruzi morphology and usually grew well in routine culture media. Metacyclic trypomastigotes were found in cultures or experimentally infected Triatoma infestans. All isolates were pure T. cruzi cultures, presenting typical 330-bp products from kinetoplast DNA minicircles, and 250 or 200-bp amplicons from the mini-exon non-transcribed spacer. Their genetic type assignment was resolved by their isoenzyme profiles. The finding of TcI in one asymptomatic patient from Paraíba was confirmed by the sequencing assay. TcVI was found in two asymptomatic individuals from Bahia and Rio Grande do Sul. TcII was identified in six patients from Pernambuco, Bahia and Minas Gerais, who presented different clinical forms: cardiac (2), digestive with megaesophagus (1), and indeterminate (3).

CONCLUSIONS:

The main T. cruzi genotypes found in Brazilian chronic patients were identified in this work, including TcI, which is less frequent and usually causes asymptomatic disease, unlike that in other American countries. This study emphasizes the importance of T. cruzi genotyping for possible correlations between the parasite and patient’ responses to therapeutic treatment or disease clinical manifestations.

Keywords:
Trypanosoma cruzi genotypes; Chronic Chagas disease; TcI; Paraíba State; Brazil.

INTRODUCTION

Trypanosoma cruzi Chagas, 1909 is the etiologic agent of the American trypanosomiasis or Chagas disease, one of the most important neglected human infections. About 6-7 million people worldwide are infected with T. cruzi, mainly in endemic areas of 21 countries of Latin America¹. Since the 1990s, several successful initiatives for controlling the parasite vectors, and preventing transmission by blood transfusion or organ transplantation have drastically reduced the number of new cases of Chagas disease². However, the international migration, generally of asymptomatic patients, from Latin American to non-endemic countries of North America (United States and Canada), Western Pacific region (mainly Japan and Australia), and Europe (Spain, Portugal, France, and other countries), has spread the Chagas disease by non-vectorial routes. Nowadays, this disease has become an emerging global health problem^3-5.

Trypanosoma cruzi is composed of heterogeneous populations of the parasite that circulate among humans, vectors, domestic animals and wild reservoirs^6-8. The high genetic variability of T. cruzi has been confirmed by different approaches, and this species was classified in different sub-groups, as zymodemes^6,7,9, major groups or lineages^10,11, and thereafter in six discrete typing units (DTUs)¹², which correspond to the six clusters of isozyme genotypes found by Tibayrenc and Ayala¹³. According to consensus among specialists, the main T. cruzi genetic types were correlated to those six DTUs, and they were renamed Trypanosoma cruzi I-VI (TcI-TcVI)^7,14,15. Subsequently, a new genotype closely related to TcI was described in Brazilian bats¹⁶ and named Tcbat or TcVII, although without consensus regarding its DTU assignment^8,17,18.

In Brazil, TcI (formerly Z1) is widely distributed among mammalian hosts within the wild cycle, mainly the common opossum, Didelphis marsupialis, but it can also be found in human acute infections and more rarely in chronic patients^6,7,19-23. Otherwise, TcII (formerly Z2) and TcVI (formerly ZB or Paraguayan Z2) are mainly restricted to hosts within the domiciliary habitats, including humans^7,8. All T. cruzi genotypes can be found in asymptomatic chronic patients. However, TcII is the most important agent of severe heart disease, including megacardia, and digestive syndromes, such as megaesophagus and megacolon, mainly in central and eastern regions of Brazil^6-8,19,20. The TcVI genotype is prevalent in Southern Brazil (Rio Grande do Sul), and it has been also associated with cardiac and digestive forms^7,8,24.

The present paper describes the characterization and DTU identification of nine T. cruzi isolates obtained from patients with chronic Chagas disease who were under ambulatory care at the Evandro Chagas National Institute of Infectious Diseases (INI, FIOCRUZ, Brazil). The finding of TcI among these isolates is emphasized, as well as the importance of the routine genotyping of samples from patients with Chagas disease to better understand possible correlations between the parasite and the human responses to drug treatment, or even disease clinical outcomes.

METHODS

Patients and trypanosome cultures

Patients with chronic Chagas disease who donated blood samples for the trypanosome isolation were under clinical care at INI and had not yet begun chemotherapeutic treatment. They presented different clinical forms and proceeded from the States of Pernambuco, Paraíba, Bahia, Minas Gerais, and Rio Grande do Sul. These patients were of both sexes and aged 44-66 years, as shown in Table 1.

TABLE 1
Data on the patients with chronic Chagas disease who donated blood for parasite isolation, and data on the isolates of Trypanosoma cruzi obtained from them, including their code number in the Trypanosomatid Collection (CT-IOC), molecular and biochemical characterization, and genotype assignment.

Data of the patients				Trypanosoma cruzi isolates			Molecular and biochemical analyses			Genotype
Patients	Age (years)	Sex	Origin (Brazilian states)	Clinical form	Stock	CT-IOC	kDNA*	Mini-exon*	Zymodeme	DTUs
L.F.S.	49	M	PE	Indeterm.	LFS49	537/542**	330	250	Z2	TcII
J.M.C.	55	M	MG	Digestive (1)	JMC55	538	330	250	Z2	TcII
M.C.J.B.	51	F	BA	Indeterm.	MCJB51	539	330	250	ZB	TcVI
L.T.A.	47	F	RS	Indeterm.	LTA47	540	330	250	ZB	TcVI
J.N.S.	65	M	PB	Indeterm.	JNS65	541	330	200	Z1	TcI***
J.M.M.	51	M	BA	Indeterm.	JMM51	543	330	250	Z2	TcII
J.J.C.	66	M	PE	Cardiac (2)	JJC66	544	330	250	Z2	TcII
M.N.A.G.	44	F	MG	Cardiac (2)	MNAG44	545	330	250	Z2	TcII
C.S.	53	M	MG	Indeterm.	CS53	553	330	250	Z2	TcII

• M: male; F: female; PE: Pernambuco; MG: Minas Gerais; BA: Bahia; RS: Rio Grande do Sul; PB: Paraíba; Indeterm.: indeterminate; (1) megaesophagus; (2) cardiac form, stage A33; CT-IOC IOC: Trypanosomatid Collection at the Oswaldo Cruz Institute; kDNA: kinetoplast DNA; DTUs: discrete typing units (TcI, TcII, TcVI). ^*Data in base pairs (bp). ^**CT-IOC 542 is a subculture of the isolate CT-IOC 537. ^***Genotype confirmed by DNA sequencing and BLAST analysis.

For trypanosome isolation in cultures, blood samples (5mL) from each patient were collected in Vacutainer^® tubes [ethylenediaminetetraacetic acid (EDTA), as an anticoagulant], divided in aliquots (~1.2 mL), and thereafter seeded into 16(150-mm screw-cap tubes containing blood-agar slants (NNN) overlaid with liver infusion tryptose broth (LIT) supplemented with 10% or 20% fetal calf serum, as described elsewhere²⁵. Positive hemocultures were subsequently maintained in LIT and/or NNN+LIT at 27.3(0.4^oC. When rich cultures from each isolate were obtained, samples of them were cryopreserved in liquid nitrogen (stabilates), which previously received a name and a code number for deposit in the Trypanosomatid Collection at the Oswaldo Cruz Institute (CT-IOC). For characterization studies, the stocks usually proceeded from stabilates, being grown in axenic cultures as aforementioned. After several passages, the subcultures only returned to the cryobank with another code number.

The following T. cruzi stocks were used as references: Y (CT-IOC 106), CL Brener (CT-IOC 005), Dm28c (CT-IOC 010), F (CT-IOC 003), and Colombian (CT-IOC 004). The references of T. rangeli were H14 (CT-IOC 038; KP1+), SC-61 (CT-IOC 272; KP1(), and two isolates from Brazilian patients with Chagas disease²⁵: US42 (CT-IOC 535) and APS56 (CT-IOC 536 and its subculture CT-IOC 546).

Parasitological characterization

For trypanosome species identification, each isolate was first analyzed with regard to its morphological peculiarities in Giemsa-stained smears, as seen under optical microscopy ((1,000), by comparing them with typical T. cruzi and T. rangeli forms^25,26. Two biometrical parameters for distinguishing these species were also examined: the total length (TL, flagellum included) of the trypomastigotes and the length of rod-like kinetoplasts at their major axis (KL) of the epimastigotes²⁵.

The biological behavior of these stocks was analyzed according to their ability to grow in routine culture media (LIT and NNN+LIT) and their cellular differentiation to typical T. cruzi metacyclic trypomastigotes. The percent of these stages was evaluated by counting 100-200 randomly chosen forms in Giemsa-stained slides. If necessary, the occurrence of metacyclics was searched in the gut of Triatoma infestans (third instar nymphs) experimentally infected through an artificial system (MM Lima: Personal Communication).

Molecular and biochemical characterization

For molecular and biochemical analyses, parasite cells from axenic ecultures of each isolate were harvested by centrifugation (1,500×g, 15 minutes, 4ºC), washed twice in saline plus EDTA (0.1M, pH 8.0), and the pellets stored in liquid nitrogen until use. Genomic DNA from each isolate was extracted using DNAzol (Invitrogen), according to the manufacturer’s instructions.

All isolates were first analyzed by polymerase chain reaction (PCR) targeted to sequences of their kDNA minicircles using the primers Tc121/Tc122, which reveal a single 300-bp amplicon (T. cruzi) or 760-bp and ~330-bp products (T. rangeli)^25,27. Thereafter, a PCR multiplex assay based on the non-transcribed spacer of the mini-exon gene was performed using the primers Tc1/Tc2/Tc3/Tr/ME^28,29, which can yield products with 200bp (TcI), 250bp (TcII and TcVI), 150bp (TcIII and TcIV), and 100bp (T. rangeli). The amplicons were electrophoresed on 1.6% agarose gels, stained with ethidium bromide, and visualized and photographed under ultraviolet light.

All isolates were also analyzed by multilocus enzyme electrophoresis (MLEE) at four selected loci, which enable the identification of T. cruzi DTUs, their mixtures, T. rangeli, and other trypanosome species^{13,24,25,28,30-33}, as follows: malate dehydrogenase (MDH, E.C.1.1.1.37), glucose phosphate isomerase (GPI, E.C.5.3.1.9), phosphoglucomutase (PGM, E.C.2.7.5.1), and malic enzyme (ME, E.C.1.1.1.40).

For T. cruzi genotype confirmation, the isolate JNS65 (CT-IOC 541) was also analyzed using a PCR assay based on a 832-bp fragment of the TcSC5D gene from the T. cruzi CL-Brener genome (TcCLB.473111.10 and TcCLB.507853.10 loci) with the primers TcSC5D-fwd (5’-GGACGTGGCGTTTGATTTAT-3’) and TcSC5D-rev (5’-TCCCATCTTCTTCGTTGACT-3’)¹⁷. The amplified products were monitored on agarose gel electrophoresis stained with 3% GelRed (Biotium). For amplicon sequencing, we used a terminator kit (BigDye, Applied Biosystems), and the sequencing was performed using a DNA analyzer (ABI PRISM^® 3730, Applied Biosystems) at the Fiocruz Genomics Technological Platform. The acquired sequences were compared with others from the GenBank through the Basic Local Alignment Search Tools (BLAST).

Ethical considerations

The inclusion of patients in this study and blood collections were performed after receiving approval from the Fiocruz Ethical Committee for Research in Humans (approval no.: 0050.0.009.000-05).

RESULTS

Trypanosome cultures and parasitological characterization

The trypanosome cultures obtained from each patient and used throughout the present work were deposited in the Trypanosomatid Collection at the Oswaldo Cruz Institute, and identified with a name and a code number (CT-IOC), as shown in Table 1.

As seen in Giemsa-stained smears under light microscopy ((1,000), all cultures only displayed typical T. cruzi stages regarding the general features of their epimastigotes and trypomastigotes with large kinetoplasts (Figure 1A-G), which were very distinct from those found in T. rangeli (Figure 1h-i). The TL of the trypomastigotes (metacyclics) averaged from 19.1(2.5μm (CT-IOC 541) to 23.2(0.5μm (CT-IOC 545), and the KL of the epimastigotes ranged from 1.6(0.2μm (CT-IOC 544) to 1.8(0.2μm (CT-IOC 553). Most of the isolates were able to grow both in LIT and NNN+LIT media, with the exception of the stock CT-IOC 538, which only grew in the latter condition. Typical T. cruzi metacyclic trypomastigotes (Figure 1A-E) were found in cultures of eight stocks at rates ranging from 2.9% (CT-IOC 538) to 19.8% (CT-IOC 543). The isolate CT-IOC 537/542 only presented metacyclics (16.7%) in the gut of experimentally infected T. infestans.

FIGURE 1
Representative forms from axenic cultures of Trypanosoma cruzi and Trypanosoma rangeli isolates from patients with Chagas disease followed at the Evandro Chagas National Institute of Infectious Diseases (INI, FIOCRUZ). Trypanosoma cruzi stages: metacyclic trypomastigotes (A-E), and epimastigotes (F, G). Trypanosoma rangeli stages: epimastigote (H), and trypomastigote (I) (CT-IOC 535). Compare the differences in size between the trypomastigotes of T. cruzi and T. rangeli, as well as their kinetoplasts. Trypanosoma cruzi genotypes are represented as follows. TcI: (A, B), CT-IOC 541. TcII: (C, D, F), CT-IOC 543 and 544. TcVI: (E, G), CT-IOC 539 and 540. Giemsa-stained smears under optical microscopy (?1,000). All images have the same magnification.

Results of the PCR using the primers Tc121/Tc122 showed that all isolates from the patients presented a single 300-bp amplicon derived from the kDNA minicircles, as the reference strain of T. cruzi (Y; CT-IOC 106) (Figure 2A). The multiplex PCR assay of the non-transcribed spacer of the mini-exon gene displayed 250-bp products in most isolates (CT-IOC 537-540, 543-545, and 553) and the Y reference strain (CT-IOC 106). Amplicons with 200bp were only found in the isolate JNS65 (CT-IOC 541) and TcI reference strains (CT-IOC 010 and 003) (Figure 2B).

FIGURE 2
Polymerase chain reaction products of Trypanosoma cruzi isolates from patients with Chagas disease followed at the Evandro Chagas National Institute of Infectious Diseases (INI, FIOCRUZ), and reference strains. A: Typical T. cruzi amplicons (330bp) derived from kDNA minicircles using the primers Tc121/Tc122. B: Amplicons from the mini-exon non-transcribed spacer using a polymerase chain reaction multiplex assay with the primers Tc1/Tc2/Tc3/Tr/ME; 200 and 250-bp bands were from TcI and TcII/TcVI genotypes, respectively. The numbers at the top of the gel indicate the code number of each stock in the Trypanosomatid Collection (CT-IOC). Trypanosoma cruzi reference strains: CT-IOC 106 (Y), 010 (Dm28c), and 003 (F). Negative control: (N). Molecular markers: ɸX174 DNA Hae digest (M1), and 100-bp ladder (M2).

The isoenzyme analysis at MDH, PGM, and ME loci clearly distinguished T. cruzi from T. rangeli (Figure 3 and Figure 4). The isoenzyme profiles of the T. cruzi stocks at GPI and PGM loci provided evidence of the zymodemes of the isolates from patients with Chagas disease, according to the reference strains (Figure 4). The Z2 pattern was found in six isolates (CT-IOC 537/542, 538, 543, 544, 545, and 553) and the Y reference strain (CT-IOC 106). The ZB pattern was found in the isolates CT-IOC 539, 540, and the CL Brener reference strain (CT-IOC 005). Only the isolate CT-IOC 541 (JNS65) presented the ZI pattern, as Dm28c and Colombian stocks (CT-IOC 010 and 004, respectively). Otherwise, only discrete differences were found at the ME loci among the T. cruzi stocks, as follows (Figure 4). All Z2 strains presented identical profiles, and they could be distinguished from ZB isolates (CT-IOC 539, 540, and 005) at the ME-2 locus, and from Z1 stocks (CT-IOC 541, 010 and 004) at the ME-1 locus, being noteworthy that the isolate CT-IOC 541 and the Colombian strain (CT-IOC 004) presented the same pattern. Results and conclusions of the biochemical and molecular analyses are summarized in Table 1.

FIGURE 3
Isoenzyme patterns at malate dehydrogenase locus displayed by Trypanosoma cruzi isolates from patients with Chagas disease followed at the Evandro Chagas National Institute of Infectious Diseases (INI, FIOCRUZ), and reference strains. The numbers at the bottom of the gel are the code numbers of each stock in the Trypanosomatid Collection (CT-IOC). Trypanosoma rangeli reference isolates from Chagas disease patients: CT-IOC 535 (US42), and 536/546 (APS56). Trypanosoma cruzi reference stocks: CT-IOC 005 (CL Brener), 106 (Y), and 010 (Dm28c). Note the clear distinction between T. cruzi and T. rangeli at this enzyme locus.

FIGURE 4
Diagrammatic representation of the electrophoretic patterns of glucose phosphate isomerase (GPI), phosphoglucomutase (PGM), and malic enzyme (ME) displayed by Trypanosoma cruzi isolates from patients with Chagas disease followed at the Evandro Chagas National Institute of Infectious Diseases (INI, FIOCRUZ), and reference strains. The numbers at the bottom of the diagram are the code numbers of each stock in the Trypanosomatid Collection (CT-IOC). Trypanosoma rangeli KP1+ and KP1- references strains: CT-IOC 272 (SC-61) and 038 (H14), respectively. Trypanosoma cruzi references stocks: CT-IOC 005 (CL Brener), 106 (Y), 010 (Dm28c), and 004 (Colombian). Zymodemes of the isolates from chagasic patients: Z1 (CT-IOC 541), Z2 (CT-IOC 537/542, 538, 543, 544, 545, and 553), and ZB (CT-IOC 539 and 540).

The acquired sequences from the amplification products of the isolate CT-IOC 541 were deposited in GenBank (accession number KX781993) and analyzed through BLAST. Its genetic similarity (99%) with several TcI strains and Tcbat (TCC1122 stock) was confirmed, as follows (GenBank accession numbers in parentheses): Sylvio X-10 (JN050585.1), PALV2 (JN050577.1), LL015 (JN050571.1), Dm28c (JN050567.1), JR cl4 (KC881183.1), Teda2 (JN050579.1), CAI72 (JN050565.1), and Tcbat (KC881185.1).

DISCUSSION

In a previous study, Sousa et al.²⁵ reported the finding of T. rangeli in two patients with Chagas disease who were under ambulatory care at the Evandro Chagas Clinical Research Institute (FIOCRUZ, Brazil), now known as INI. In the present paper, nine trypanosome isolates from patients with Chagas disease who were also followed at INI were characterized by different techniques for identifying the trypanosome species and its genetic type. Using classical parasitological approaches, such as the parasite morphological features (Figure 1), biometrical data, growth, and differentiation in routine culture media, all isolates under study were T. cruzi^25,26,34. The confirmation that they were pure cultures was evidenced by their single 330-bp amplicon derived from the kDNA minicircles^25,27, and their products from the mini-exon gene non-transcribed spacer^28,29 (Figure 2), which had 250bp in most isolates and 200bp only in one stock (CT-IOC 541) identified as TcI. The isoenzyme analyses also confirmed the presence of T. cruzi in all isolates (Figure 3), as well as resolved their DTU identification^24,31,32,33 (Figure 4 and Table 1).

The TcII genotype (formerly Z2) is the main agent of chronic Chagas disease in Brazil, and it can cause severe cardiomyopathy and digestive megasyndromes^7,8,19,20. This genotype was found in isolates from six patients, two with the cardiac form in stage A³⁵ (CT-IOC 544, 545), one with megaesophagus (CT-IOC 538), and the others with the indeterminate form (CT-IOC 537/542, 543, and 553). It is worth mentioning that the patient with megaesophagus proceeded from the Minas Gerais State, where this clinical form has been associated with TcII^7,36. Although the present study did not aim to determine correlations between biological features of T. cruzi strains and Chagas disease clinical manifestations, it is interesting to note that the isolate from the patient with megaesophagus (CT-IOC 538) was the most fastidious in cultures, presenting the lowest rates of metacyclic trypomastigotes. The DTU TcVI (formerly ZB) was found in two isolates (CT-IOC 539 and 540), both from asymptomatic patients, one of them originating from the Rio Grande do Sul State, where this genotype is prevalent.

The finding of TcI (formerly Z1) in Brazilian patients with chronic Chagas disease is infrequent, and it usually produces mild disease, although its pathogenicity in acute infections is similar to that caused by TcII^19,20. In the present study, TcI was identified in a single isolate (CT-IOC 541) from a chronic patient with the indeterminate form, who originated from the Paraíba State (Northeastern Brazil). A sequencing assay followed by BLAST analysis displayed its higher genetic similarity (99%) with several TcI strains, first Sylvio X10, a stock originally of a human case from the Pará State (Northern Brazil), besides a Tcbat stock^16,17.

The genotype TcI had already been found in two patients from the Paraíba State by Barnabé et al.³⁷, and in three individuals from another close State (Rio Grande do Norte) by Câmara et al.³⁸. However, these authors did not mention their clinical forms. Barnabé et al.³⁷ also found TcI in Triatoma pseudomaculata, T. brasiliensis, and Didelphis albiventris from Paraíba, thus evidencing the existence of epidemiological conditions for circulation of this genotype there. Teixeira et al.³⁹ also isolated a TcI strain (José-IMT) from the myocardium of an end-stage chronic patient also from the Paraíba State. This is an uncommon disease outcome caused by this genotype in Brazil, but it had been previously described by Barrett et al.¹⁹ in a chronic patient from another Northeastern State (Bahia). More recently, Martins et al.²³ found TcI in chronic patients from the State of Rio Grande do Norte, three being asymptomatic, two with the cardiac form, and one with the digestive form. The finding of digestive form in an individual infected with TcI is surprising, since it is uncommon in Brazil and Latin American countries where this DTU is the main agent of Chagas disease^7,8.

In Southeastern Brazil, the genotype TcI was reported in five chronic patients from the State of Minas Gerais^40,41, three of them being asymptomatic and two others presenting clinical forms typically caused by TcII, which is prevalent in that state, thus suggesting mixed infections. More recently, Sangenis et al.⁴² identified TcI mixed with TcVI in an asymptomatic patient from the Rio de Janeiro State. Otherwise, in the Amazon region (Northern Brazil), TcI is the prevailing DTU found in humans as the agent of acute infections^6,7,21, but this genotype was also identified in fourteen chronic patients with the indeterminate form of Chagas disease^22,40.

Unlike that generally occurs in Brazil, TcI is the main agent of chronic Chagas disease in some American countries (e.g., Venezuela and Colombia), where the patients can develop severe and fatal cardiomyopathy (usually without digestive megasyndromes), as well as meningoencephalitis in immunocompromised individuals^6-8,43-50. Such discrepancy deserves further investigations, but many factors should be considered for attempting to explain it, as the genetic diversity of both parasites and human beings, and the epidemiological conditions that favor the selection of T. cruzi genotypes by local vectors and hosts^51-53.

TcI is the most abundant and widely dispersed of all T. cruzi genotypes, being found from the Southern North America to the Northern regions of Argentina and Chile⁵⁴. The high genetic diversity within TcI was clearly shown by Tibayrenc and Ayala¹³, and thereafter mentioned by several authors^7,8,55,56. Analysis of the spliced-leader intergenic region (SL-IR) of several TcI stocks evidenced five SL-IR groups (TcIa-TcIe) correlated with transmission cycles^57-60. Other molecular studies displayed seven or three TcI subpopulations associated with their geographic distribution^54,61. Llewellyn et al.⁵⁴ disclosed an exclusively domestic genotype (Ven_DOM), subsequently named TcI_DOM, which corresponds to the TcIa SL-IR group⁶¹. More recently, León et al.⁵⁶ suggested the subdivision of TcI only into two main groups (TcI_DOM and sylvatic), proposing a PCR assay for identifying them. In the present study, the sequencing analysis of the TcI isolate (CT-IOC 541) showed that it is genetically closer to Sylvio X10, a stock identified as TcId⁶⁰, a sub-group related to sylvatic cycles, which was also found by Câmara et al.³⁸ in Northeastern Brazil. It is worth mentioning that TcId (or TcI sylvatic) was identified in the heart and brain of patients with severe Chagas disease outside Brazil^46,49. In the present study, the isolate CT-IOC 541 and the Colombian strain showed the same banding pattern at the ME-1 locus, which was distinct from that of the Dm28c stock (Figure 4), a finding that corroborates the variability within TcI.

Several authors have found correlations between the Trypanosoma cruzi type and responses to chemotherapeutic treatments^20,41,62-68. Together, these reports evidenced that the TcI strains were usually the most resistant to trypanocidal treatment, TcII stocks presented greatly variable responses, and TcVI isolates were the most susceptible. However, these associations have not been fully confirmed by other authors^69-71. Accordingly, further long-term studies are necessary to investigate this issue, especially those monitoring the treatment responses of patients with Chagas disease whose parasite DTU has been identified. Routine T. cruzi genotyping can be feasible at medical centers with scientific research support, since presently, there are several available molecular techniques for its characterization^8,14,17,72, and the classical MLEE analysis can reveal the main genetic groups, mixed stocks, and other trypanosome species^14,25,30-33. Despite some controversies and exceptions, nowadays there are recommendations for treating all patients with chronic Chagas disease using new dosing strategies and drug combinations for preventing side effects, thus increasing the chances of treatment completion and monitoring of patients for a longer time^73-75. Identification of the T. cruzi genotype in samples from patients is also important to better understand the possible influence of the parasite type on the clinical manifestations of the human Chagas disease, as it seems to occur in individuals infected with TcI, who rarely present digestive forms.

Acknowledgments

We acknowledge Mrs. Sheila Medeiros dos Santos Pereira and Edna Maria da Silva for technical assistance, Dr. José Jurberg for donating the triatomine bugs, Drs. Adeilton Brandão and Luiz Ney d’Escoffier for supporting the parasite molecular typing (IOC, FIOCRUZ), and the Fiocruz Genomics Technological Platform.

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• This study received financial support from Fundação Oswaldo Cruz, Universidade Federal Fluminense, and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro.

Publication Dates

• Publication in this collection
  Jan-Feb 2017

History

• Received
  06 Oct 2016
• Accepted
  02 Dec 2016