Feeding behavior of triatomines from the southwestern United States: An update on potential risk for transmission of Chagas disease

Abstract

Chagas disease is an emerging infectious disease in North America due to the immigration of individuals from endemic areas. The parasite has been transmitted to patients in non-endemic areas by blood transfusion and organ donation. Only six autochthonous cases have been described in humans in the United States yet the parasite is widespread among native mammals and resident triatomines are competent vectors. We attempted to determine if common southwestern triatomines, Triatoma protracta and Triatoma rubida have the potential to amplify the disease among human residents of the Southwest. The defecation patterns of the bugs were studied while feeding upon immobilized mice. Wild-caught adult male and female triatomines were observed feeding one to three times for a total of 71 observed feedings. T. rubida (15 bugs) appeared to be more aggressive, beginning feeding shortly after being placed in proximity to the host (within 2.3 min) whereas Triatoma protracta (12 bugs) was more deliberate, beginning feeding, on average, at 4 min. There were 40 observations of T. rubida, which fed for 27.9 ± 13.6 min, whereas T. protracta fed for 22.8 ± 7.5 min (n = 31). Bugs were weighed pre- and post-feeding and T. rubida females ingested > T. protracta females > T. rubida males > T. protracta males. Weight gain did not correspond to the feeding duration. Defecation occurred on 42% of the feedings (30 of 71), and no bugs defecated on the host. The majority of the defecations occurred within 1 min of feeding, usually at the time of repletion. A large proportion of defecations occurred after the bugs left the vicinity of the host. All bugs and at least one fecal smear from each feeding bug were tested for Trypanosoma cruzi and 21% of T. protracta were positive by PCR (4 bugs and 1 feces). No T. rubida tested positive for T. cruzi. The bugs’ defecation pattern is similar to that reported >50 years ago. Furthermore, there is no indication that they are becoming more domesticated in the desert Southwest. Thus, based on our observations, we do not believe that T. protracta and T. rubida pose an imminent risk for transmission of Chagas disease to residents of the southwestern United States.

Introduction

Chagas disease, caused by Trypanosoma cruzi, is an emerging public health concern in the United States and Canada principally because of its potential to contaminate the blood transfusion supply. Immigration to the United States of asymptomatic, infected individuals from endemic areas in Latin America has led to transmission of the disease through donor blood (Young et al., 2007) as well as through surgical implantation of infected donor organs to patients in non-endemic areas (Mascola et al., 2006). Seroprevalence of infection is notable among immigrants in Miami and Los Angeles (Leiby et al., 2002), some of whom have PCR evidence of ongoing parasitemia (Leiby et al., 2008). The parasite has been found in over 18 species of mammals in the United States (John and Hoope, 1986) as well as six autochthonous cases of Chagas in humans. One case each was reported from California (where Triatoma protracta (Uhler) was implicated) (Schiffler et al., 1984) and Tennessee (Herwaldt et al., 2000), three cases from Texas (Woody and Woody, 1955, Ochs et al., 1996) and the most recent case involved a woman in Louisiana whose house and surroundings were heavily infested with T. sanguisuga (Leconte) (Dorn et al., 2007).

This study set out to determine whether or not the feeding behavior of T. protracta and Triatoma rubida (Uhler), posed a significant risk for transmission of Chagas disease to humans in the Southwest at the current time. These two species are known vectors of T. cruzi (Guzman-Bracho, 2001). Triatomine bites are common in the Southwest (Lynch and Pinnas, 1978), but are mainly feared because of their potential to cause anaphylaxis (Wood, 1942, Wood, 1950). Wood studied T. protracta and T. rubida as possible vectors of Chagas disease in the southwestern United States over 50 years ago (Wood, 1951).

We studied wild-caught, adult triatomine feeding behavior on immobilized mice, measuring their feeding duration and blood intake, recording where they fed on the mouse and whether or not they defecated after feeding. We documented how far from the host they defecated and also determined whether or not they were infected with T. cruzi.