Chagas disease remains a significant public health issue in many parts of the world despite its discovery one hundred years ago, and is estimated to account for more than 10,000 cases of deaths in 2008. In Latin America alone, it is estimated that 25 million people live in high-risk areas, and 7 to 8 million people have the disease1,2. The etiologic agent of Chagas disease is the protozoan Trypanosoma cruzi(Kinetoplastida: Trypanosomatidae), which is transmitted by insects of the subfamily Triatominae (Hemiptera: Reduviidae)3. In the past, Triatoma infestans was responsible for the highest number of Chagas disease cases4, and in 1983, the World Health Organization (WHO) conducted a vector control program to eradicate T. infestans by means of chemical control, dwelling improvements, and reeducation of the exposed population.
Following these efforts, Chagas disease transmitted by T. infestans or blood transfusion was eradicated by 20065. However, residual vector foci remain in the States of Bahia, Minas Gerais, and Rio Grande do Sul4. T. infestans are the major vectors for Chagas disease because they are exclusively domestic, highly anthropophilic, and easily infected by T. cruzi. The wide distribution of T. infestans has been attributed to transport associated with human migration and enhanced species adaptation to the intradomicilliary environment, including sheltering within wall cracks, roofs, human apparel, under beds, and additional micro-habitats6. Additionally, studies have shown frequent human infection in areas of concentrated T. infestans7. Recently, a resident of Ibipeba observed the presence of a triatomine in his dwelling, raising important epidemiological questions regarding the immergence of triatomine foci and transmission of Chagas disease. The objective of this study was to identify Triatominae foci in Ibipeba, Bahia, and to collect and characterize each identified species.
This was a cross-sectional epidemiological study of data collected by the entomology team of the Epidemiological Surveillance Board of the Bahia State Bureau of Health (Diretoria de Vigilância Epidemiológica, Secretaria da Saúde do Estado da Bahia, DIVEP/SESAB) in November 2009. The research was conducted in the City of Ibipeba, after a resident identified a triatomine specimen in his dwelling located in the urban area of the city. The City of Ibipeba is located in the State of Bahia within the country of Brazil (Figure 1A and 1B). Ibipeba is in the mesoregion of Irecê and the physiographic area of Northern Chapada Diamantina (encompassing the entire Drought Polygon characterized as the cerrado biome). Triatomines were collected on an Amaralina farm (at an altitude of approximately 593m with the coordinates 11°61.297′ S, 42°11.283′ W).
FIGURE 1 – Geographical location of the study ecotope. A) The map of South America indicates the location of our Triatominae species survey. The City of Ibipeba is in the State of Bahia, which is one of 26 states in Brazil. B) Image of the Ibipeba ecotope where Triatoma infestans was initially discovered.
Environments consisting of domestic units closed by doors (i.e., houses and annexes) were considered domestic ecotopes. Triatomines were discovered sheltering within infrastructure cracks of the domestic environments and under beds or behind objects placed along walls. The studied peridomestic ecotopes (where domestic or wild animals sleep or are bred) were in a radius of 50m from the dwellings. During the field research, triatomines were collected manually with tweezers and placed in individual flasks labeled with information regarding the place of collection8.
Entomological indicators were calculated according to standard equations: index of domiciliary infestation = (number of domiciliary units with triatomines / number of domiciliary units searched) × 100; index of domiciliary triatomine density = number of samples captured / number of domiciliary units searched; index of colonization = (number of domiciles with nymphs / number of houses inspected) × 1009.
The initial reference point for investigation of Triatominae foci was the dwelling first reported to house a triatomine specimen. From this reference point, 9 locations were surveyed in Ibipeba. The initial T. infestans specimen (Figure 2A) discovered in Ibipeba was identified using an entomological key6 at the entomology laboratory of the 21st Regional Health Board in Irecê. Images shown in Figure 2Bdemonstrate traces of triatomine feces on intradomicile walls that corresponded to the presence of specimens identified in that area. The image in Figure 2C indicates that wild animals, as armadillo, were bred in the peridomicile where triatomine specimens were identified. Figure 2D demonstrates a tree trunk (Leucaena leucocephala) located approximately 50 m from a rural residence (Amaralina farm in Ibipeba) where T. infestans nymphs and adults were identified.
FIGURE 2 – Discovery of Triatoma infestans at the study ecotope. A) Image of an adult Triatoma infestansspecimen captured inside a dwelling in Ibipeba. B) Image depicting traces of triatomine feces on a dwelling wall. C) Wild animal breeding in the peridomicile of a dwelling in Ibipeba. D) Image demonstrating the tree bark where Triatoma infestans nymphs were discovered in association with rodents.
Three triatomine species were discovered in the intradomicile and peridomicile regions of study ecotopes as shown in Table 1. The species were T. infestans (183 specimens), Triatoma sordida (176 specimens), and Triatoma pseudomaculata (13 specimens). The calculated indices of domiciliary infestation, domiciliary density, and colonization were 14%, 1.32, and 1%, respectively. Overall, 280 domiciliary units were surveyed and triatomine were discovered in 39 of the units. T. pseudomaculata and T. sordida adult specimens and T. infestans adult and nymph specimens were found in three of the dwellings.
TABLE 1 – Number of collected triatomine species in Ibipeba, Bahia, Brazil according to ecotope.
| Species | Ecotope | Total | |||
|---|---|---|---|---|---|
| intradomicile | peridomicile | ||||
| n | % | n | % | ||
| Triatoma infestans | 16 | 8.7 | 167 | 92.3 | 183 |
| Triatoma pseudomaculata | 13 | 100.0 | 0 | 0.0 | 13 |
| Triatoma sordida | 174 | 98.8 | 2 | 1.2 | 176 |
| Total | 203 | 54.5 | 169 | 45.5 | 372 |
Over the last 5 years, initiatives such as the T. infestans Eradication Program (Programa de Erradicação do Triatoma infestans (PETi)), which use insecticides to target T. infestans, have been conducted throughout Brazil. These initiatives and large-scale entomological surveys carried out since 1975 have shown extensive distribution of T. infestans (711 Brazilian cities with domestic infestation)10. In 1983, approximately 190,000 specimens of T. infestans were collected during surveys, while by 1993, only 83 cities reported T. infestans infestation. In 1998, the number of specimens decreased to 485, and in 2007, only 205 specimens were captured from 21 dwellings in 13 cities11.
Although the State of Bahia and Brazil as a whole were considered free from T. cruzi transmission by T. infestans and blood transfusions in 1995 and 20065, respectively, interventions to control spread of Chagas disease must continue. This is due to the presence of other transmitting species (e.g., Panstrongylus megistus, Rhodnius prolixus, Triatoma brasiliensis, Triatoma maculata, T. pseudomaculata, and T. sordida) that colonize human environments in many areas of Brazil.
Although T. sordida and T. pseudomaculata are less likely to transmit Chagas disease when compared to T. infestans, these species are a continual risk for the emergence of new cases of the disease. Furthermore, a recent survey conducted in 2009 in Macaúbas, Bahia, discovered that Triatoma lenti adults and nymphs also carried an isolated T. cruzi strain13. Additionally, a serological survey carried out in Mulungu do Morro, Bahia, suggested the existence of vector transmission of T. cruzi14. These studies demonstrate that vector transmission persists despite breakthroughs in the control of Chagas disease. These findings question the efficacy of insecticide use and indicate a possible resistance to alpha-cypermethrin 20% SC, an insecticide recommended by the Ministry of Health11 for domestic use.
The results from this study demonstrate the presence of T. infestans, T. pseudomaculata, and T. sordida in Ibipeba, Bahia, for the first time. Discovery of T. infestans specimens in a tree trunk located in the peridomicile (50 m from a dwelling) is a novel finding, as there are few reports of similar observations in Brazil12. This finding indicates the possibility of T. infestans colonies infesting the extradomicile, thus undermining intervention and control programs only intended to control the vector in the peri- and intradomicile. Importantly, this study demonstrates that vectors could infest dwellings in subhuman conditions. This indicates the need for public authority involvement in controlling infestation beyond the typical range of the health sector.
