Fine-Scale Predictions of Distributions of Chagas Disease Vectors in the State of Guanajuato, Mexico

Abstract

One of the most daunting challenges for Chagas disease surveillance and control in Mexico is the lack of community level data on vector distributions. Although many states now have assembled representative domestic triatomine collections, only two triatomine specimens had been collected and reported previously from the state of Guanajuato. Field personnel from the stateÕs Secretarṍa de Salud conducted health promotion activities in 43 of the 46 counties in the state and received donations of a total of 2,522 triatomine specimens between 1998 and 2002. All specimens were identiÞed, and live insects examined for Trypanosoma cruzi. In an effort to develop Þne-scale distributional data for Guanajuato, collection localities were georeferenced and ecological niches were modeled for each species by using evolutionary-computing approaches. Five species were collected: Triatoma mexicana (Herrich-Schaeffer), Triatoma longipennis (Usinger), Triatoma pallidipennis (Stål), Triatoma barberi (Usinger), and Triatoma dimidiata (Latreille) from 201 communities located at elevations of 870 Ð2,200 m. Based on collection success, T. mexicana had the broadest dispersion, although niche mapping indicates that T. barberi represents the greatest risk for transmission of Chagas disease in the state. T. dimidiata was represented in collections by a single adult collected from one village outside the predicted area for all species. For humans, an estimated 3,755,380 individuals are at risk for vector transmission in the state, with an incidence of 3,500 new cases per year; overall seroprevalences of 2.6% indicate that 97,640 individuals are infected with T. cruzi at present, including 29,300 chronic cases. . Nine of these species are considered as primary vector species (Ramsey et al. 2003), and most belong to two species complexes (phyllosoma and protracta) in the genus Triatoma (Lent and Wygodzinsky 1979). Multiple triatomine species are frequently found within a single region or state in Mexico. As a result, Ͼ71% of the Mexican population is at direct risk of acquiring T. cruzi infections from triatomines, and Ͼ96% of all T. cruzi transmission occurs via these vectors (Ramsey et al. 2003). KEY WORDSOne of the most signiÞcant challenges for Chagas disease surveillance and control in Mexico is the lack of Þne-scale (at the level of local communities) vector distribution data, as well as the almost complete ignorance of the diseaseÐtransmission characteristics and risk areas, both by the public health community and by at-risk populations. With improved malaria control in the country, in the last decade, "additional" operative vector control activities have focused primarily in urban environments owing to increases in classical and hemorrhagic dengue transmission. (To date, vector-borne disease control activities are budgeted only for malaria in the country.) Moreover, the recent decentralization of primary health care services to the state level has emphasized the need and the opportunity to review local and state health care prio...

Projected Future Distributions of Vectors of Trypanosoma cruzi in North America under Climate Change Scenarios

“…Chagas disease is controlled by using insecticides and improvements in housing, but such publicly organized programs do not exist in the United States, partly due to lack of information regarding human cases, vector-parasite incidence, and reservoirs of the disease. Studies that can provide baseline data for addressing these critical concerns should combine field work, molecular analysis (e.g., examining blood meals of triatomines) and ecological modeling techniques to assess the potential for Chagas disease at a fine-geographic scale (e.g., areas at most risk for Chagas disease; see [38]) are encouraged. Findings from that work can be used to advise health program managers in their efforts to control or prevent transmission of Chagas disease effectively and provide a cost-effective method of predicting locations of high transmission risk of this disease, particularly in light of the economic burden that Chagas disease might represent (similar or higher than other diseases such as rotavirus, cervical cancer, or Lyme disease [39]).…”

Phylogeny and Niche Conservatism in North and Central American Triatomine Bugs (Hemiptera: Reduviidae: Triatominae), Vectors of Chagas' Disease

“…the growth of transportation networks and inter-locality human movement or migration) [85], [86]. Since NCA triatomines are both sylvatic and synanthropic [12], [59], [87], [88], they are prone to suffer involuntary translocations due to human migration. A well-documented case of this dispersal process was the Central American and southern Mexico invasion of Rhodnius prolixus [89].…”

“…This species succeeded in sub-tropical forest areas in southern Mexico and CA, although it was never collected in conserved habitats, possibly because niche conservatism prevented the species from establishing outside its ecological requirements. Recent distribution shifts for NCA triatomines have been recorded based on extra-range collections for T. dimidiata and sylvatic T. nitida and T. mazzottii [59], [88], [90]. The latter two records are inside the ecological range of each species, as predicted using niche conservatism analysis, but outside reported distribution areas.…”

“…Only one sister species pair ( T. gerstaeckeri – T. mexicana ), was defined based on data from the single locus analysis of both cytb and ITS2, while the rest were supported with the multilocus analysis. Georeferenced occurrence locations reported elsewhere were used to build ENM models [12], [27], [59] (see Ibarra-Cerdena et al [12]) for a description of occurrence dataset sources). Niche models were constructed for members of each species for pairs, using 188 data points for T. barberi , 477 for T. dimidiata group 2, 42 for T. dimidiata group 1a, 235 for T. gerstaeckeri , 115 for T. longipennis , 42 for T. mazzottii , 265 for T. mexicana , 22 for T. nitida , 33 for T. phyllosoma , 154 for T. p. protracta , 44 for T. recurva , and 42 for T. rubida (Table S4).…”

The potential for emergence of Chagas disease in the United States

“…Wood (1938) described the northward range expansion of T. protracta in California, but since that time, research on the triatomine's range has been limited in the United States with the exception of modeling the species' range in parts of Texas Beard et al, 2003). Modeling efforts have mapped the triatomine range in much of Latin America (Abad-Franch et al, 2001;Costa et al, 2002;Peterson et al, 2002;Guzman-Tapia et al, 2005;López-Cárdenas et al, 2005;Bustamante et al, 2007). In particular, Peterson et al (2002) applied the genetic algorithm for rule-set prediction (GARP) model to the T. gerstaeckeri species' range in Mexico to evaluate the environmental characteristics under which the disease agent and vector thrive.…”