Infestation with T. infestans
A major reason for the spread of Chagas’ disease throughout Bolivia and Latin America is the domestication of T. infestans (see Appendices 5 and 6). In endemic areas of the disease in Bolivia, T. infestans has invaded domestic areas to a staggering degree. The percentages of infestation for houses in the departments of Bolivia are as follows: Cochabamba, 38.2 percent; Chuquisaca, 78.4 percent; Tarija, 78.2 percent; La Paz, 42.2 percent; Potosi, 62.5 percent; and Santa Cruz, 96.5 percent (SOH/CCH 1994:20; Valencia 1990a:44). Thus, 70 percent of houses in the most populated departments of Bolivia are infested with T. infestans.
Once they are inside domestic areas, triatomines hide in a variety of places. Of 1,090 vinchucas gathered from 191 houses, 529 were in the walls, 46 in the roof, 48 in the beds, 324 in the peridomicile area, and 143 in surrounding corrals (Valencia 1990a:42-65). All vinchucas were identified as T. infestans: 581 (53 percent) were nymphs and 509 (47 percent) were adults. The infestation rate for homes in the study area was 92 percent (Valencia 1990a:44).
The medium index of vinchucas with T. cruzi parasites was 31 percent, with the index reaching as high as 53 percent in one community (Valencia 1990a: 44). Some 46 percent of the infected vinchucas were found in dormitories, which indicates that they transmit T. cruzi best among sleeping humans. Infection rates within the nymph stages was 25 percent; within the adult stage it was 37 percent. The vector was infected incrementally with T. cruzi from its initial nymph stages to adult stages. [16]
T. infestans is accountable for 97 percent of the cases of Chagas’ disease in Bolivia; twelve other species account for the remaining 3 percent. The most prominent of these species are T. guasyana, T. melanocephala, T. oswaldoi, and T. venosa, which are primarily sylvatic, prey on wild animals, and spread Chagas’ disease among such animals. This becomes another threat to the threatened and depleted species of wild animals in the Andes and Amazon. Large numbers of Triatoma infestans and lesser numbers of Triatoma sordida are found in every department of Bolivia except Oruro, which is located at an elevation of 3,500 meters.
Triatoma infestans usually inhabits areas at elevations from 1,100 to 11,200 feet (330 to 3,450 m.) above sea level; nevertheless, it has been found at higher elevations, such as Llallagua, Potosi, at 13,300 feet (4,100 m.) (Borda 1981:16). Sylvatic triatomine vectors of T. cruzi are primarily found within forested areas of the departments of Beni, Pando, and Santa Cruz and within the Yungas area of the Department of La Paz. Sylvatic triatomines spread Chagas’ disease more in animals than in humans within the departments of Santa Cruz, Beni, and Pando, although they do infect some forest dwellers.
Although T. infestans are found throughout Bolivia, the insects prefer warm and humid conditions, being found more in the lower elevations and warmer climates of the central regions and the lowlands rather than in the highlands such as La Paz and the Altiplano. Chagas’ disease occurs primarily in the valleys, plains, and forests lying between elevations of 1,000 to 11,400 feet (300 and 3,500 m.) above sea level. Roughly 84 percent of Bolivian territory lies within this zone. Some 47 percent of Bolivia’s populace reside in endemic areas of the disease, thereby placing approximately 3 million people at risk for Chagas’ disease. Many more Bolivians are also at risk because of possible infection through blood transfusions in non-endemic urban areas (Ault 1992, Schmunis 1991, Valencia 1990a).
Rates of household infestation of T. infestans are higher in rural and periurban areas of Bolivia; but urban infestation has increased significantly with increased urban migration and rapid transportation between rural and urban areas. Infestation rates presently are 70-100 percent for rural areas, 40- 60 percent for peri-urban areas, and 20-40 percent for urban areas (SOH/CCH 1994). A general average is that 50 percent of vinchucas found anywhere in Bolivia are infected with T. cruzi parasites. This percentage increases proportionally as more people become infected with these parasites and pass them on to uninfected vinchucas. In endemic areas, T. cruzi passes rapidly from sick persons to healthy persons, because vinchucas prey on different people, many of them sleeping together, until virtually all the hosts are infected with Chagas’ disease.
Adaptation of Bolivians and Bugs
The spread of T. cruzi throughout Bolivia is accomplished by certain selective and adaptive mechanisms of vinchucas. A combination of nocturnal predation, crawling and gliding, and transformation through nymph stages, means that there are bugs with different sizes, air and land mobility, and the cover of darkness in which to hide, move, and draw blood from humans, easily targeting those sleeping in run-down adobe houses with thatched roofs.
Vinchucas are sensitive to light, and, at the laboratory for Proyecto Chagas at the National University at Cochabamba, biologist J. Delgado keeps them in loosely covered jars during the day. As he explained to me, “as long as there’s light in the room, they stay as still as sleeping sloths.” Reaching into the jar with pinchers, he grabbed a vinchuca around the thorax and held it. It remained motionless, occasionally wiggling its antennae, while I photographed it (see Figure 14). He then replaced the vinchuca in a tightly covered jar and draped a dark cloth over its top and sides; within seconds you could hear this vinchuca moving about inside the jar.
Figure 14. Laboratory assistant at Chagas Project at the Universidad San Simon in Cochabamba holding a vinchuca bug that will be used to diagnose victims of Chagas’ disease. Uninfected vinchucas are placed under the armpit for thirty minutes to draw blood; thirty days later their feces are examined for T. cruzi. This diagnostic test is called xenodiagnosis and is commonly used throughout Bolivia to determine parasite population and zydomenes. Indirect ELISA tests are frequently used first to determine antibodies to T. cruzi. (Photograph by Joseph W. Bastien) When vinchucas are caught in the light of day, they appear to be friendly domesticated bugs, neither biting, kicking, or trying to get away. Not surprisingly, many Bolivian children play with them. Boys race the bugs, and some put them in girls’ lunch boxes. Girls gather their rice-shaped eggs in tiny wicker baskets, pretending they are chicken eggs. Even some adults consider the insects’ eggs to be good omens predicting fertility or a bountiful harvest. They are referred to as “harbingers of good luck,” “kissing bugs,” “friends,” and “toys.” Their perceived personalities disassociate these bugs from their disease-carrying capability.
Attitudes about vinchucas were revealed in the following conversation I had with Sarah Arredondo outside of Tarija, Bolivia, in 1997 (see Figure 15). Sarah was seven years old at the time and had been bitten while she was sleeping by a vinchuca, which her mother removed from under her nightie. Her mother squashed it against the floor and blood squeezed out. Sarah said that she didn’t mind vinchucas and was unaware that they caused sickness. Sarah wants to be a hairdresser because she likes to dress up dolls. She coyly expressed herself, slightly twisting her head to purse her lips to hide shyness, which eventually turned into a smile. She then told me how her ducks ate vinchucas. Sarah’s mother hated vinchucas and had grown up in a house filled with them. She said that they were inside the house and that she had removed unnecessary items
