An Appraisal of the Status of Chagas Disease in the United States (eBook)

Chapter 1 Introduction and Historical Background

After critically reviewing old and new literature, a general picture of the situation of Chagas disease in the United States is presented by the authors. In the first two chapters, besides an historical background, several aspects of the local transmission potential by the vectors are presented; their distribution, present relationship with human dwellings, infection rates with T. cruzi, ethology and bionomics, and the severe allergic reactions they may cause are discussed. In another chapter, the zoonotic angle of the disease is considered; both wild and domestic reservoirs are described, and the epidemiological importance of some animals such as wood rats, opossums, raccoon, and dogs is stressed. There is a chapter dedicated to the different characteristics of the locally isolated parasites, including experimental infections and molecular genotype analysis. The final chapter discusses the present situation concerning the disease in human beings; specifically, indigenous cases, serological prevalence, blood transfusion, congenital and organ transplant transmission, the disease in immigrants, and laboratory-acquired infections. An overview is presented that considers the disease as a new endemic disease that is transmitted in certain areas of the country by a vector; the burden to the United States caused by Latin America immigrants who carry the disease with them is also considered. This book will help to create greater awareness about the status of Chagas disease in the United States and will help in the evaluation of certain parameters from the standpoints of ecoepidemiological and public health, facilitating future control actions.

Keywords: Chagas disease, triatomines, Trypanosoma cruzi, wood rat, United States

Chagas disease (American trypanosomiasis) was named after the Brazilian physician Carlos Justiniano Ribeiro Chagas, who in 1909 announced to the world the discovery of this new parasitic disease in animals and humans, in the town of Lassance, State of Minas Gerais, Brazil. In 1908, Chagas observed, for the first time, flagellate forms of the parasite in the intestine of the hematophagous bug Panstrongylus megistus (initially called Conorhinus megistus), which he found residing in human dwellings in Brazil. A few months later, he studied the parasite by experimentally infecting monkeys, rodents, and dogs. At the beginning of 1909, Chagas discovered the same flagellate in the blood of a cat and in a 2-year-old girl and realized that he had discovered a new disease-causing agent, transmitted by hemipteran insects in the family Reduviidae, subfamily Triatominae. He named the new trypanosome Schizotrypanum cruzi, which was later renamed Trypanosoma cruzi. The enzootic condition of the new trypanosomiasis was also demonstrated by Chagas after he found a natural infection in an armadillo (Dasypus novemcinctus) and a bug (Panstrongylus geniculatus) sharing the same burrow (Chagas, 1909a, 1909b, 1912; Coura, 1997).

According to the classical WHO data, it was estimated that Chagas disease affected 16–18 million people with at least 100 million at risk of contracting the infection in 21 countries throughout Latin America. There were an estimated 1 million new cases of chronic disease and some 45,000 deaths annually (WHO, 1991, 1995). Recent data indicate that these figures have been reduced drastically to less than 10 million, mainly due to the action of the various control “initiatives” throughout Latin America. Marked reductions in incidence and prevalence have been observed since the Southern Cone Initiative was launched in 1991, with consequent important savings in healthcare expenditures for the countries (Moncayo and Ortiz-Yanine, 2006; Schofield et al., 2006; Yamagata and Nakagawa, 2006). Likewise, the efforts toward the total elimination of Rhodnius prolixus from the Central American subregion, a target of the Central American Initiative, have been extremely successful (cf. Zeledón et al., 2008). In fact, the transmission of Chagas disease by R. prolixus is presently considered to be interrupted in the entire subregion, due to its apparent elimination (OPS, 2011).

In the United States, the parasite was first observed in California in another species of bug, Triatoma protracta, a few years after Chagas’ initial observation (Kofoid and McCulloch, 1916). Nevertheless, when these authors failed to find the blood forms in the natural host of the bug, the wood rat (Neotoma fuscipes), they thought that the flagellate they had found was a different species and named it Trypanosoma triatomae. Furthermore, according to Kofoid and Donat (1933a) at that time, they were unable to transmit the parasite to laboratory albino rats through the bite of the infected insects. Later on, Kofoid and Donat (1933a, 1933b) succeeded in infecting laboratory and wild Neotoma rats plus one opossum (Didelphis virginiana) through T. protracta-infected feces, demonstrating that the previously observed flagellate present in the bug was indeed the same trypanosome described by Chagas in Brazil several years earlier. These authors stressed the fact that, of the six subspecies of N. fuscipes present in California, they found that the bugs (T. protracta) in Neotoma fuscipes macrotis and Neotoma fuscipes annectans nests, but only those associated with the former wood rat were infected with T. cruzi (Kofoid and Donat, 1933b).

The experiments were extended by Wood (1934a, 1934b), who proved that in fact Triatoma protracta and N. fuscipes are natural hosts of the parasite, that it is possible to experimentally infect different mammals (including rhesus monkeys and dogs), that amastigotes are formed in tissues of the infected animals, and that the infections tend to be light, suggesting a low virulence of the trypanosome.

Also in the 1930s, T. cruzi infections were discovered in other species of bugs such as Triatoma uhleri (also known as Triatoma rubida) in Arizona (Kofoid and Whitaker, 1936) and Triatoma sanguisuga and Triatoma gerstaeckeri in Texas (Anonymous, 1938; Packchanian, 1939). Additional species were also later found infected as indicated below. An interesting antecedent is that T. sanguisuga was reported from the state of Georgia as early as 1855 by Le Conte, who made the observation that people, particularly children, were bitten by the bug there (Le Conte, 1855). The same species was confirmed in Georgia by Stal (1859) a few years later. Similarly, this species was found in beds and reported to bite humans in Illinois in counties such as Madison, Jersey, Union, and Adams (Walsh and Riley, 1869). Uhler (1876, 1878) made reference to T. sanguisuga as inhabiting Virginia, Maryland, Ohio, Texas, Florida, and Illinois and pointed out that it was a “blood-thirsty tenant of the beds in houses.” Ryley and Howard (1892) presented evidence of Conorhinus sanguisugus (T. sanguisuga) biting humans in Missouri and Oklahoma (Indian Territory). In the latter place, the bugs were in a bed in a log house, and apparently representatives of the species were also reported in the forests. Kimball (1894) found this bug, in large numbers, in poultry houses and in barns attacking horses, and occasionally in houses in Manhattan, Kansas, causing serious allergic reactions in people. A similar situation was pointed out by Marlatt (1896) in parts of Texas and Kansas, where the insect was a frequent visitor of homes.

John Lembert made observations of humans bitten by T. protracta in the Yosemite Valley in the 1860s (Mortensen and Walsh, 1963). Thurman (1944) mentioned the first finding of Triatoma neotomae in Texas by Schwartz in 1898, even though the specimens were not properly identified at that time.

In 1899, there were several nationwide newspaper releases, originating with the story of a lady from Washington D.C. who developed a severe reaction when bitten on the face by one of these insects (T. sanguisuga). This seems to be the origin of the common name “kissing bug,” used for the first time on that occasion (Howard, 1899; Shields and Walsh, 1956). Other common names found in the American literature are cone-nosed bug, bloodsucker, Mexican bed bug, China bug, and assassin bug.

Stal (1859) makes reference to other species of the same group being present in the United States, including C. gerstaeckeri and C. variegatus (aka Triatoma lecticularia) in Texas. Uhler (1876) also mentions the presence of the latter species in California, Georgia, Louisiana, and Illinois. Ryley and Howard (1893) reported that in Washington County, Florida, T. lecticularia “frequently fly into houses.” Howard (1899) added that C. protracta was present in California, Arizona, and Utah and included Missouri in the distribution of C. sanguisugus.

Collectively, these reports demonstrate that triatomine vectors of Chagas diseases have existed in the United States, under wild conditions, for many centuries, and that some species have been associated with human dwellings for a long time, causing allergic reactions of varying degrees...