Chagas Disease Vectors of Espírito Santo, Brazil: First Report of Triatoma infestans (Klug, 1834) (Hemiptera, Triatominae) in the Brazilian State and Development of an Identification Key Based on Cytogenetic Data

Abstract.

Chagas disease is a potentially life-threatening illness caused by the protozoan Trypanosoma cruzi and transmitted, mainly, by hematophagous insects of the Triatominae subfamily. In Brazil, there are currently about 66 triatomine species distributed throughout the country’s 27 states. Triatoma infestans is considered as a species of great vectorial importance, mainly because of its biological characteristics, such as the high degree of anthropophilia, adaptation to the home environment, ability to withstand long periods of fasting, and present a wide geographical distribution. Taking into account the epidemiological importance of these species, we carried out the first report of T. infestans in the Espírito Santo, Brazil, and development of an identification key for all species notified in that state, based on cytogenetic data. This information is important because they contribute to the direction of epidemiological surveillance activities carried out by vector control programs of the Espírito Santo, Brazil.

Chagas disease is a potentially life-threatening illness caused by the protozoan Trypanosoma cruzi (Chagas, 1909) (Kinetoplastida, Trypanosomatidae) and transmitted, mainly, by hematophagous insects of the Triatominae subfamily (Hemiptera, Reduviidae).^1,2 An estimated 8 million people are infected with T. cruzi worldwide, mainly in Latin America where this disease remains one of the biggest public health problems, causing incapacity in infected individuals and more than 10,000 deaths per year.¹

Vector control remained the most effective method of preventing transmission of this neglected disease in Latin America,¹ because of the 154 species described (grouped into 19 genera and five tribes),^3–8 more than 130 were reported in this region of the American continent,⁹ and all are considered as potential vectors of Chagas disease.

In Brazil, there are currently about 66 triatomine species distributed throughout the country’s 27 states,^3,10 being five of them with greater importance in the domiciliary transmission of Chagas disease, namely, Triatoma brasiliensis (Neiva, 1911), Triatoma pseudomaculata (Corrêa and Espínola, 1964), Triatoma sordida (Stål, 1859), Panstrongylus megistus (Burmeister, 1835), and Triatoma infestans (Klug, 1834).³ In the state of Espírito Santo, for example, there are seven species notified (P. megistus, Panstrongylus diasi [Pinto and Lent, 1946], Panstrongylus geniculatus [Latreille, 1811], Cavernicola pilosa [Barber, 1937], Rhodnius domesticus [Neiva and Pinto, 1923], Triatoma tibiamaculata [Pinto, 1926], and Triatoma vitticeps [Stål, 1859]), with T. vitticeps being the most prevalent species.⁹

Triatoma infestans is considered as a species of great vectorial importance, mainly because of its biological characteristics, such as the high degree of anthropophilia, adaptation to the home environment, ability to withstand long periods of fasting, and present a wide geographical distribution.^11,12 Although there are currently only rare residual foci in Rio Grande do Sul and Bahia¹³ (because of the success of the control programs of the Ministry of Health that resulted in a reduction of 99.3% reduction in the number of specimens captured between 1983 and 1997),¹³ this triatomine has been reported in 17 Brazilian states: Alagoas, Bahia, Goiás, Maranhão, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Paraná, Paraíba, Pernambuco, Piauí, Rio de Janeiro, Rio Grande do Sul, Santa Catarina, Sergipe, São Paulo, and Tocantins.³

Based on a survey carried out in the entomological collection of Museum of Zoology of the University of São Paulo, São Paulo, Brazil, the presence of a specimen of T. infestans deposited from the state of Espírito Santo was observed, which was collected in 1956 (Figure 1A and D) (time when chemical control with pyrethroids had not yet been implemented in Brazil).^14,15 Taking into account the epidemiological importance of these species, we carried out the first report of T. infestans in this Brazilian state and development of an identification key for all species notified in that state, based on cytogenetic data.

Figure 1.

(A) Male specimens of Triatoma infestans; (B) head and thorax detail of T. infestans; (C) connexivum detail of T. infestans; and (D) specimen label. This figure appears in color at www.ajtmh.org.

The morphological pattern of the specimen analyzed (and which confirms to be a T. infestans based on the keys of Lent and Wygodzinsky¹⁶ and Galvão³) was 1) black neck with a pair of yellowish side spots (Figure 1B); 2) pronotum totally black, fore lobe with a pair of disc tubers and small lateral tubers, and hide lobe rough (Figure 1B); 3) rugged black scutellum (Figure 1B); 4) legs completely black with the trochanters and base of the yellowish femurs (Figure 1B); 5) anterior and middle femurs with a pair of small subapical denticles (Figure 1B); and 6) black connexivum, being each segment with a large yellow spot away from the anterior suture, but closely close to the border of the posterior segment (Figure 1C).

Based on the keys of Borsatto et al.,^17,18 cytogenetic data available in the literature (karyotype and constitutive heterochromatin pattern in chromatin and chromosomes) for the six of the seven species notified in Espírito Santo (with the exception of P. diasi that does not present cytogenetic data available in the literature) more T. infestans were grouped and used for the construction of the identification key (Table 1).³

Table 1.

Key for the triatomines of the Espírito Santo state based on cytogenetic data

Identification key
1. Karyotype with 2n = 21 chromosomes (18A + X1X2Y)	Panstrongylus megistus
2. Karyotype with 2n = 22 chromosomes (20A + XY)	3
3a. Prophase without heterochromatin blocks dispersed inside the nucleus	Cavernicola pilosa
3b. Prophase with heterochromatic blocks dispersed inside the nucleus	4
4a. Heterochromatin in 3–4 large pairs of autosomes	Triatoma infestans
4b. Heterochromatin in some autosomes	Rhodnius domesticus
5. Karyotype with 2n = 23 chromosomes (20A + X1X2Y)	6
6a. Prophase without heterochromatin blocks dispersed inside the nucleus	Panstrongylus geniculatus
6b. Prophase with heterochromatic blocks dispersed inside the nucleus	Triatoma tibiamaculata
7. Karyotype with 2n = 24 chromosomes (20A + X1X2X3Y)	Triatoma vitticeps

The ento-epidemiological surveys in Espírito Santo show that T. vitticeps is the most prevalent species in the state.⁹ This species that has a high rate of natural infection by T. cruzi¹⁹ has already been found in domiciliary regions,²⁰ being associated with some autochthonous cases of Chagas disease in the state.^21,22 However, the prevalence of human infection by T. cruzi in this state has always been low in surveys carried out in the general population, among schoolchildren or in blood banks,^21,23 which resulted in the classification of Espírito Santo as an epidemiological surveillance area where vector control measures need not be adopted.²² However, Santos et al.¹⁹ highlight that the high natural infection rates observed for Espírito Santo reinforce the need to maintain entomological surveillance in areas where this vector occurs.

Several species of triatomines have recently been reported in Brazilian states: Rhodnius montenegrensis (Rosa et al., 2012) in Amazonas²⁴; T. sordida and Rhodnius neglectus (Lent, 1954); Rhodnius stali (Lent, Jurberg, and Galvão, 1993); R. montenegrensis, P. megistus, and Panstrongylus rufotuberculatus (Champion, 1899); Panstrongylus lignarius (Walker, 1873) in Acre^25–31; P. lignarius and P. megistus in Rondonia^29,32; and, now, T. infestans in Espírito Santo. These ento-epidemiological surveys are of great importance for public health because the knowledge of fauna (local, regional, municipal, and/or state) of triatomines directly assists in the activities of vector control programs.

In addition to the notification of the presence of T. infestans in Espírito Santo, the development of the identification key based on cytogenetic data is also an alternative for assisting in the activities of vector control programs because the correct classification of triatomines is essential for biological, ecological, and epidemiological data to be recovered by health agents (which can direct in choosing the prophylactic measures to be adopted).

Borsatto et al.^17,18 developed keys for São Paulo, Alagoas, Amapa, Ceara, Roraima, and Santa Catarina based on cytogenetic data. Although most identification keys are based on morphological data,³ the use of cytogenetic data is an alternative tool for morphological keys (mainly for species that are difficult to distinguish, such as species of the genus Rhodnius³³). In addition, the classic cytogenetic techniques (such as those used to obtain the aggregated results in the Espírito Santo identification key) are extremely simple and of low cost, which allows their use by health agents.

So, we notified for the first time the presence of T. infestans in the state of Espírito Santo, and we developed an identification key based on cytogenetic data for the triatomine species present in that Brazilian state, contributing to the direction of epidemiological surveillance activities carried out by vector control programs.