Historical overview

Historical data allow us to infer that when the Europeans arrived in the New World, there was already a local knowledge of triatomine insects, including their habits and some biological characteristics directly related to man; however, these insects were not known to be associated with the disease first described by Carlos Chagas in 1909.

Geronimo de Bibar, Chilean author of a chronicle from early 1500, writes “for six years now there is a type of bugs that sting very badly and give little itching, they are as big as cockroaches and their time is in summer.”³³ Various chroniclers, such as Antonio de Ciudad Real, also make references to bugs with wings. There are other references to bugs with wings that correspond to Triatominae (i.e., kissing bugs, pitos hyphae, hocicones) (texcan in Nahuatl, pec in Maya, and yta in Quechua). Lizarraga also refers to this group of insects saying the following about Bolivia and Argentina:

Here called hyphae, cockroaches (black), as large as the insects found in the ships of the North Sea, and that color, with wings: but with the difference that they are almost invisible, they sting and bite so delicately at night that it is not felt after the fire is finished, however after two days a welt rises as a bean, so itchy it is insufferable (...) The insects are afraid of fire, and when the fire goes out they fall down the walls or from the ceiling and bite the sleeper in the legs, in the head and face (. ..) They have clumsy feet, and when they have filled their bellies with the blood they have sucked, cannot walk.

Felix de Azara also describes these bugs “like flat beetles,” adding the important observation that “when defecating on the wound, they leaved an indelible stain.”

When describing the existence of “vinchucas” in Venezuela, the Jesuit Jose Gumilla, reports that the bite is painless, however, once the arthropod detaches, unbearable itching pain occurs. In Peru, especially in the area of Charcas, Bernabe Cobo comments that they are harmful, locate their victims by scent, and are known by the natives as hyphae.³⁴

Archeological excavations have been carried out along the Aleutian Islands and the west coasts of Canada and the United States, as well as on the west coasts of Central and South America. The origin and spread of humans coincided with the latter part of the Pleistocene ice ages, and the geographical distribution of early humans was influenced by these ice ages in a number of ways. All of the excavations have yielded evidence of the presence of human activity since nearly 15,000 years ago. However, the precise date of the first human presence on the continent may be even earlier, as far back as 20,000—25,000 years, although this is still a matter of debate among archeologists. For the purpose of this chapter, it is safe to conclude that humans were spreading south and east of North America and that these small bands of hunter gatherers had reached the northern tip of South America around 10,000—12,000 years ago.²³

This amount of time was enough for the adaptation of various parasitic diseases to their new hosts. Cultural developments, such as agriculture and permanent or semipermanent settlement patterns, created an ideal environment for the spread of infectious diseases, including tuberculosis and syphilis. Human cultural adaptation to warm and humid environments allowed Chagas disease to spread widely.

The epidemiological pattern of T. cruzi reveals that primitive transmission was restricted to established cycles in tropical forest environments. The parasite was spread via anal gland secretions and urine from opossums and later via triatomine insects that fed on small mammals in broad areas of the South American continent, with no human intervention in this natural cycle. This would suggest a balance between species.

Because of long periods of adaptation, the parasite has a wide range of wild mammal reservoirs, including D. marsupialis, P. opossum, D. novemcinctus, T. tetradactyla, S. sciurius, C. satanas, and bats of the genus Phyllostomus. The same situation persists today in the wild, where the disease maintains an enzootic epidemiological character. The presence of T. cruzi does not seem to significantly affect triatomines nor does it impact mammals that have been naturally infected. Humans might then have become infected as a single addition to the already extensive host range of T. cruzi, which also includes other primates.

Human Chagas disease is a purely coincidental occurrence. As humans came into contact with the natural foci of infection and caused different degrees of ecological transformations, infected triatomine insects were forced to occupy their dwellings.^23,35

Thus began a process of adaptation and domiciliation to human habitations through which the vectors had direct access to abundant food as well as protection from climatic changes and predators. A good example of this adaptation is T. infestans, the main vector of T. cruzi in the Southern Cone countries of South America. T. infestans is considered to be an almost exclusively domiciliary species, and the same is true for R. prolixus in the northern region of South America and Central America.²³

Estimates have been made about the age of the order Xenarthra (which contains armadillos, anteaters, and sloths), one of the four major clades of placental mammals reported to be hosts for T. cruzi. All four of these clades were isolated in South America following its separation from the other continental land masses. Xenarthrans diverged over a period of about 65 million years, leaving more than 200 extinct genera and only 31 living species.

The next placental mammal T. cruzi reservoirs to emerge in South America were the caviomorph rodents and platyrrhine primates during the Eocene. These clades appear following colonizations by rafting or island hopping across the Atlantic Ocean from Africa by their respective most recent ancestors. The continental isolation ended when the Isthmus of Panama land connection between South and North America emerged approximately 3.5 Mya in the Pliocene, marking the beginning of the Great American Biotic Interchange.²⁵ In regard to mammals, the northern invaders of South America included carnivores, insectivores, noncaviomorph rodents, lagomorphs, artiodactyls, and perissodactyls. However, bats are conspicuously absent in this scenario despite their contribution to 20% of the mammalian species diversity.

Based on molecular dating, interordinal diversification occurred in Laurasia during the Cretaceous, including the appearance of bats estimated at 85 Mya²⁶ (Fig. 2.3).