Summary: Chagas' disease is caused by the protozoan parasite Trypanosoma cruzi and causes potentially life-threatening disease of the heart and gastrointestinal tract. The southern half of the United States contains enzootic cycles of T. cruzi, involving 11 recognized triatomine vector species. The greatest vector diversity and density occur in the western United States, where woodrats are the most common reservoir; other rodents, raccoons, skunks, and coyotes are also infected with T. cruzi. In the eastern United States, the prevalence of T. cruzi is highest in raccoons, opossums, armadillos, and skunks. A total of 7 autochthonous vector-borne human infections have been reported in Texas, California, Tennessee, and Louisiana; many others are thought to go unrecognized. Nevertheless, most T. cruzi-infected individuals in the United States are immigrants from areas of endemicity in Latin America. Seven transfusion-associated and 6 organ donor-derived T. cruzi infections have been documented in the United States and Canada. As improved control of vector- and blood-borne T. cruzi transmission decreases the burden in countries where the disease is historically endemic and imported Chagas' disease is increasingly recognized outside Latin America, the United States can play an important role in addressing the altered epidemiology of Chagas' disease in the 21st century.

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Trypanosoma cruzi and Chagas' Disease in the United States

The enormous amount of literature on Chagas' disease makes it almost impossible to present a review of all its aspects, a task that would require the collaboration of numerous specialists. This review presents mainly some ecological aspects, with particular emphasis on the ethology of insect vec­ tors and their participation in transmission of the disease. Finally, we discuss some human social factors related to ecological and epidemiological aspects of the disease.

Chagas' disease: an ecological appraisal with special emphasis on its insect vectors.

Distribution and characterization of canine Chagas disease in Texas.

Data were pooled from multiple sources including newly collected triatomine specimens, preserved specimens, government reports, and scientific articles to create a biogeographical profile of triatomine vector species found in Texas. Triatomine specimens were documented in 97 of 254 counties, and Trypanosoma cruzi-infected specimens were reported from 48 counties. Triatomine specimens were distributed in 11 of the 12 ecoregions in Texas, with all but one species found in multiple ecoregions. Of the 241 newly collected specimens, 50.74% were infected with T. cruzi. Triatoma gerstaeckeri was the most frequently collected and most geographically dispersed species followed by T. sanguisuga. Three species, T. gerstaeckeri, T. sanguisuga, and T. lecticularia, were associated with human dwellings, and over half of the new specimens found inside or near houses were infected with T. cruzi. Chagas disease vectors in Texas are widely distributed and have adapted to ecologically diverse settings. The high T. cruzi infection prevalence of specimens found in close proximity to human settings suggests the presence of an active peridomestic Chagas disease transmission cycle.

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Biogeography and Trypanosoma cruzi infection prevalence of Chagas disease vectors in Texas, USA.

Trypanosoma cruzi, the causative agent of Chagas' disease, is a substantial public health concern in Latin America. Although rare in humans and domestic animals in the United States, T. cruzi is commonly detected in some wildlife species, most commonly raccoons (Procyon lotor) and Virginia opossums (Didelphis virginiana). To increase our understanding of the reservoir host species range and geographic distribution, 11 species of mammals from six states spanning the known range of T. cruzi (Arizona, California, Florida, Georgia, Missouri, and Virginia) were tested for antibodies to T. cruzi using indirect immunofluorescent antibody testing. In addition, culture isolation attempts were conducted on a limited number of animals from Georgia and Florida. Evidence of T. cruzi was found in every state except California; however, low numbers of known reservoirs were tested in California. In general, the highest seroprevalence rates were found in raccoons (0-68%) and opossums (17-52%), but antibodies to T. cruzi were also detected in small numbers of striped skunks (Mephitis mephitis) from Arizona and Georgia, bobcats (Lynx rufus) from Georgia, two coyotes (Canis latrans) from Georgia and Virginia, and a ringtail (Bassariscus astutus) from Arizona. Culture-based prevalence rates for raccoons were significantly greater than those for opossums; however, seroprevalences of raccoons and opossums from several geographic locations in Georgia and Florida were not different, indicating that exposure rates of these two species are similar within these areas. For both raccoons and opossums, seroprevalence was significantly higher in females than in males. No difference was detected in seroprevalence between adults and juveniles and between animals caught in urban and rural locations. Our results indicate that T. cruzi prevalence varies by host species, host characteristics, and geographic region and provides data to guide future studies on the natural history of T. cruzi in the United States.

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Seroprevalence of Trypanosoma cruzi Among Eleven Potential Reservoir Species from Six States Across the Southern United States

TrypanOsoma cruzi (Chagas) was isolated from 17 of 126 (13.5%) opossums and 5 of 35 (14.3%) raccoons from east-central Alabama. Inoculation of blood, heart muscle, kidney tissue, urine, and peritoneal fluid from survey animals into NNN or Chang's medium showed that the organism was most often isolated from heart muscle followed by blood, kidney, peritoneal fluid, and urine. The trypanosome was recovered from 11 of 181 (6%) triatomid bugs collected in the same area. Of the 44 collections, 32 were from hollow trees or stumps, 10 were from human habitations, and 2 from the quarters of domestic animals. In some instances, both infected vectors and reservoirs were found in heavily populated areas. Trypanosoma cruzi (Chagas), the etiologic agent of Chagas' disease, was first reported from triatomid bugs and man by Chagas (1909). Subsequent reports showed the organism to be present in many areas of Latin America. The first report of T. cruzi in the United States was that of Kofoid and McCulloch (1916), who found the flagellate in triatomid bugs in California. At the time, they named the organism Trypanosoma triatomae since they could not find the organism in the blood of wood rats upon which the bugs were feeding. Later reports verified the presence of T. cruzi in vertebrate reservoirs and triatomid bugs in the southwestern United States (Kofoid and Donat, 1933; Kofoid and Whitaker, 1936; Wood and Wood, 1941). Woody and Woody (1955) reported the first naturally acquired human case of Chagas' disease in the United States in a child from Corpus Christi, Texas. In the same year, a second indigenous case, also diagnosed in a child, was reported from Bryan, Texas, according to a report by Goble (1958). Walton et al. (1956) reported the isolation of T. cruzi from three raccoons captured in Maryland; however, they were unable to find triatomid vectors in the area where the raccoons were captured, according to a report in 1958. McKeever et al. (1958) reported finding an organism resembling T. cruzi in 107 animals of four species in southwestern Georgia and northwestern Florida. Later research verified that the organism was T. cruzi (Norman et al., 1959). Yaeger (1961) found inf cted triatomid bugs in areas of Louisiana where mammals harboring trypanosomes had been collected. These reports indicate that T. cruzi is probably present throughout the southeastern United States. This paper reports the incidence of T. cruzi in wild mammals and triatomid bugs collected in east-central Alabama between September 1960 and June 1963.

Jon P. Shoemaker

Papers

Incidence of trypanosoma cruzi (chagas) in wild vectors and reservoirs in east-central alabama.

Occurrence of Macracanthorhynchus ingens Meyer, 1933, in a West Virginia Raccoon

Trombicula fitchi (Loomis, 1954) in West Virginia