Community-Based Entomological Surveillance Reveals Urban Foci of Chagas Disease Vectors in Sobral, State of Ceará, Northeastern Brazil

Abstract

Background: The aim of this work was to explore the potential risk of vector-borne Chagas disease in urban districts in northeastern Brazil, by analyzing the spatiotemporal distributions and natural infection rates with Trypanosoma cruzi of triatomine species captured in recent years. The main motivation of this work was an acute human case of Chagas disease reported in 2008 in the municipality of Sobral.

Methodology/principal findings: We analyzed data from community-based entomological surveillance carried out from 2010 to 2014. Triatomine natural T. cruzi infection was assessed by examination of insect feces by optical microscopy. Sites of triatomine capture were georeferenced through Google Earth and analyzed with ArcGIS. A total of 191 triatomines were collected, consisting of 82.2% Triatoma pseudomaculata, 7.9% Rhodnius nasutus, 5.8% T. brasiliensis, 3.7% Panstrongylus lutzi, and 0.5% P. megistus, with an overall natural infection index of 17.8%. Most infestations were reported in the districts of Dom José (36.2%), Padre Palhano (24.7%), and Alto do Cristo (10.6%). The overwhelming majority of insects (185/96.9%) were captured inside houses, and most insects tended to be collected in intermittent peaks. Moreover, captured triatomines tended to constitute colonies. The acute case reported in 2008 was found to be situated within a T. pseudomaculata hotspot.

Conclusion: The triatomine collection events carried out by dwellers were aggregated in time and space into distinct foci, suggesting that insects are intermittently and artificially introduced into the city, possibly via accidental migration from their natural reservoirs. The relatively high T. cruzi infection rate indicates considerable circulation of the parasite in these areas, increasing the risk of vector-borne Chagas disease infection. These data suggest a need to strengthen epidemiological surveillance and integrate appropriate control actions targeting triatomines, T. cruzi reservoirs, and human populations. Our data also identify Chagas disease transmission as a hazard in urban areas of Sobral.

Fig 1. Location of the municipality of Sobral, Ceará State, northeastern Brazil.

Collection sites were georeferenced with Google Earth (base map modified from IBGE (ftp://geoftp.ibge.gov.br/recortes para fins estatísticos/malha de setores censitários/censo2010/base de faces de logradouros).

Fig 2. Landscapes of Sobral, Ceará, Brazil.

A: Aerial view of the city. In the background one can observe the Serra da Meruoca, a region of preserved forest near the city; B: Modern buildings in the city center; C: Chickens and domestic devices piled in the peridomicile; D: Clay house with cracks, vulnerable to colonization by triatomines; E: Garbage accumulated in a shed, attractive for rodents; F: Waste accumulated in a yard, site potentially harboring triatomines.

Fig 3. (A, B)—Mapping of the triatomine distribution in the urban area of Sobral.

A—Relative distribution of the collected triatomine species: the chart sizes indicate the total number of the captured specimens, whereas pies displays the percentage of collected species. B—Spatial distribution of collected triatomine species related to PIT spots.

Fig 4. Numbers of triatomine insects found in the urban area of Sobral, Ceará, Brazil, from 2010–2014, according to species by month and year.

Fig 5. Map of the spatial distribution of the triatomines collected in the urban region of Sobral, Ceará, Brazil.

The pictures framed in blue (A) represent the distribution mapping of triatomine species collected in Sobral residences (Triatoma pseudomaculata, Rhodnius nasutus, T. brasiliensis, Panstrongylus lutzi, and P. megistus); the pictures framed in yellow (B) represent Trypanosoma cruzi infection among the examined triatomines; the pictures framed in blue (C) represent the distribution of T. pseudomaculata; and the pictures framed in yellow (D) represent T. cruzi infection in T. pseudomaculata.