The biology of triatomine bugs native to south central Texas and assessment of the risk they pose for autochthonous Chagas' disease exposure
American trypanosomiasis (Chagas' disease) is a well-recognized cause of cardiac arrhythmia, cardiomyopathy and heart failure in Mexico and Central and South America with sporadic autochthonous cases being documented in the southern United States. In an attempt to assess the risk for Chagas' disease exposure in the region, Texas Health Service Region 8 (HSR8) was surveyed for triatomine bug vectors in an attempt to better characterize their distribution, rate of infection with the parasite Trypanosoma cruzi, and their species-specific biology. Between May 2010 and August 2013, a total of 542 triatomine bugs representing all 5 known indigenous species ( Triatoma gerstaeckeri, Triatoma lecticularia, Triatoma sanguisuga, Triatoma protracta and Triatoma indictiva) were collected from over 40 sites across the 28 county region, most of which were recovered from within or on human habitations. Triatoma gerstaeckeri was the species most commonly found in the peridomestic and domiciliary microhabitats, representing over 80% of the total number of triatomines collected during the 39-month period. The appearance of adult T. gerstaeckeri in and around human habitations exhibited a definite seasonal trend that was consistent from year to year over the three-year period of investigation. The first adult T. gerstaeckeri typically appeared in late April and was followed a rapid increase in emergence that reached a peak in mid-May to early June across HSR 8. After mid June, the rate of adult T. gerstaeckeri emergence sharply declined and then continued at a low level out to the month of October resulting in a curve that was skewed to the right. Unlike the other triatomine species native to Texas, T. gerstaeckeri was characteristically a late night species with many specimens being collected after midnight. On homes constructed with available cervices in the exterior walls, adult T. gerstaeckeri were frequently observed emerging from or entering these protective microhabitats. This observation suggests that T. gerstaeckeri readily colonizes the exterior compartment of the walls of some human habitations, suggesting that the species may be exhibiting a trend towards domestication. Occasional variably-sized nymphs were also recovered from inside the living space of several homes across the region suggesting there to be some level of home colonization in Texas. None of the other 4 native triatomine species demonstrated a distinct pattern of temporal emergence or were observed colonizing the walls of homes. Laboratory testing of triatomines by PCR (minicircle and/or TCZ loci) demonstrated an overall T. cruzi infection rate of 64.4% across all five native Triatoma species and a T. gerstaeckeri-specific infection rate of 64.0% across HSR 8. Monitoring the T. cruzi infection rate over the period of adult bug emergence demonstrated a statistically significant increase (p<0.01) in the infection rate adult T. gerstaeckeri in the later aspect (beyond June 1) of the seasonal emergence peak. This finding suggests that many of the T. cruzi-infected adult T. gerstaeckeri found on or in human habitations either fly in from the surrounding environment, or acquire the parasite around the home as adults. Regardless of the species involved, triatomine infestation of human dwellings across the region appeared to be most common in rural homes or those on the outer fringes of cities and towns, most notably in areas in close proximity to tracts of undisturbed native habitat. In most situations, triatomine bug infestations in Texas HSR 8 were characterized as being largely seasonal and transient in nature, with a low level colonization of the internal living compartment of the home occurring in some instances. These findings are similar to those reported in parts of southern Mexico and Central America where the triatomine species Triatoma dimidiata and Triatoma pallidipennis persist as transient seasonal vectors that annually infest and occasionally colonize human dwellings. Reports of human bites and the recovery of blood-engorged adult bugs from human beds were common across the region with a total of 41 well documented human exposure cases during the 39-month study. Of the five species of native triatomines in the region, only T. gerstaeckeri, T. lecticularia and T. sanguisuga were implicated in human bites. The results and observations noted during this study show that T. gerstaeckeri is a widespread and common peridomestic triatomine species across Texas HSR 8 and suggests that this species has some notable synanthropic tendencies. The high rate of T. cruzi infection in our native triatomines once again documents that Chagas' disease is endemic to south central Texas and suggests that the risk of human exposure to T. cruzi may be higher than previously thought. Because of this, Chagas' disease should be considered on the list of differential diagnoses for cases of cardiac arrhythmia and heart failure in both humans and domestic animals from south-central Texas. (Abstract shortened by UMI.)
Wozniak, Edward J, "The biology of triatomine bugs native to south central Texas and assessment of the risk they pose for autochthonous Chagas' disease exposure" (2013). Texas Medical Center Dissertations (via ProQuest). AAI1552333.