pueblos, as distinct from campesinos, or farmers) replace these antiquated buildings with new ones; rather, they build alongside the old ones, thus providing areas for triatomines. This helps explain why 139 families are living in category x housing and an almost equal number, 135 families, are living in category z housing. It also explains why the density index (which is derived from the number of bugs captured divided by the houses investigated) is high (2.5). The fact that housing in B1 is fairly divided between categories x, y, and z places all residents at risk, because triatomines will travel over 1,000 meters in search of blood meals.
Similar explanations more readily apply to stratum B2, which has 45.51 percent of the houses infested, a density rate (5.2) double that of B1, and an accumulation index of 11.4. Within B2, 55 percent of the homes fall within category z and 27 percent within category y, which increases the probability for infestation.
The peasants in stratum C suffer the same risk as those in stratum B2, with similar indices for infestation (45.51 percent), density (5.2), and accumulation (11.9); also, 55 percent of households fall within category z. The major difference is that the sample (1,226) in stratum C is much larger than the sample (309) in B2. An obvious conclusion is that Bolivians living in small communities (200 to 1,000 inhabitants), smaller hamlets, and farms suffer from high rates of triatomine infestation due to their living conditions and large number of domestic animals. More than half the houses within these strata have dirt floors, thatched roofs, cloth ceilings, and adobe walls, usually unplastered. Also, 17,588 animals were counted (25 percent dogs, 13 percent cats, 27 percent pigs, and 35 percent guinea pigs). The census did not include poultry such as chickens, ducks, and geese that attract and provide blood meals for triatomines but are not subject to, or hosts of, Chagas’ disease. Bird nests also provide favored hiding places for triatomines.
Even though lower-class strata have a higher incidence of infestation than other strata, within urban centers and peri-urban peripheral areas triatomines are spreading because of massive migration, both permanent and seasonal, from rural areas in Bolivia to industrialized areas. Housing can be even worse in these crowded areas, with scores of people living in rapidly constructed dwellings.
The percentage of vectors positive for T. cruzi in parts of Bolivia was indicated by a study done in 1991 by the SOH/CCH Chagas Control Pilot Program (1994). It conducted a baseline study within the departments of Chuquisaca, Cochabamba, and Tarija of 1,037 houses (93.6 percent coverage of the areas’ 1,108 houses); examined 4,128 blood samples from persons living in the houses (64 percent were seropositive for Chagas’ disease); and collected 13,000 peri- and intradomiciliary vectors. My analysis of these results indicates that Cochabamba had the lowest percentage of houses with basic services (only 3 percent had latrines, and none had potable water and electricity) and the lowest percentage (38.6) of houses infested by vectors positive for T. cruzi, with 46 percent of the insects carrying the parasite. The availability of latrines, potable water, and electricity does not appear to correlate with infection rates. Tarija has the highest percentage of electricity, 55.6 percent, and the highest percentage50 percentof intradomiciliary vectors positive for T. cruzi. This calls into question the notion that lighting would keep photosensitive triatomines outside of the house.
Environmental and climatic factors play a key role in the epidemiology of Chagas’ disease. The Department of Tarija is a sub-Andean region, around 6,400 feet in elevation, with a warm, dry winter season. Temperature fluctuates from 64 to 77°F, and the area receives 28 inches of rain a year, beginning in October and subsiding in March (Munoz 1977). This climate is preferred by triatomines, as there are no severe cold spells to immobilize the insects. The principal cultivation is of semitropical fruits, coca, coffee, grapes, and cocoa, and many of these plants provide nesting sites for triatomines. Some of this region has been cleared for cattle range, destroying wildlife and plants and forcing triatomines to invade houses. Less hospitable to vinchucas, the Department of Cochabamba is a mesothermic valley (at 8,310 feet) of the Cordillera Cochabamba. Temperatures fluctuate from 54 to 72°F, and rainfall is 26 inches, falling mainly between November and March. Principal cultivation is of corn, potatoes, wheat, barley, fruits, and vegetables. The Department of Chuquisaca is a sub-Andean temperate zone with a median temperature of 59°F and an average altitude of 8,200 feet above sea level. This department also includes lower regions, which might explain its high triatomine infestation and infection rates discussed in Chapter 8.
APPENDIX 6
House Infestation in Latin America
Similar statistics to those in Bolivia (see Appendix 5: House Infestation in Bolivia) are found in endemic areas for Chagas’ disease in other countries of Central and South America (Briceno-Leon 1990). For Central America, equally high infestation rates of from 30 to 70 percent are reported for three-fourths of El Salvador (OPS 1982:3); 25 percent of vinchuca bugs examined there were infected with T. cruzi. In endemic areas of Honduras 15 percent of houses are infested (Ponce 1984), and one vector, T. dimidiata, has spread to urban settings of the capital, where a family of middle-class professionals reported an acute case of Chagas’ disease in 1989 (Briceno-Leon 1990:24). In Costa Rica, 35 percent of the houses are infested, with an average of 22 triatomines per house (Zeledon et al. 1975). Some 31 percent of the triatomines and 12 percent of the people of Costa Rica are infected with T. cruzi. Six percent of the population in Guatemala are infected with T. cruzi; and, in Panama, 3 to 22 percent are infected (WHO 1985). (See Appendix 7.)
In South America, 100 percent of the houses in endemic areas of Argentina are infested with T. cruzi, and 8 percent of children under eight years are infected with Chagas’ disease (Pavlone et al. 1988:103-5). Around 30 percent of the houses in the northern half of Chile are infested with vinchucas, and 17 percent of the insects carried T. cruzi (Schofield, Apt, and Miles 1982; Flores et al. 1983; Schenone et al. 1985). In Uruguay, Chagas’ infection rates range from 1 to 7 percent for people over twelve years old (Salvatella 1986); and, in Paraguay, all rural areas are endemic for the disease, with infection rate percentages between 22 and 72 percent being reported (Arias et al. 1988; WHO 1985).
Even though Brazil has made a concerted effort to prevent Chagas’ disease, it ranks as one of the most endemic areas in Latin America. About 4.5 percent of the rural population have antibodies against the parasite; 5 million Brazilians have Chagas’ disease and another 25 million are at risk. In the Federal District of Brazil, 4.3 percent of all deaths are attributed to Chagas’ disease (Dias 1987, Pereira 1984).
In Peru, endemic regions are Arequipa, Moquegua, and Tacna, with 12 percent infection rates. Colombia has an even higher infection rate of 16 percent of the houses infested with triatomines, and 30 percent in the Departamento del Norte de Santander.
Venezuela has more than 1 million people with Chagas’ disease. Roberto Briceno-Leon (1990) presents a carefully researched analysis of the relationship of housing to Chagas’ disease in Venezuela. Within the last fifty years, Venezuela has had zones where 54 percent of the people were seropositive for Chagas’ disease. One epidemiological study conducted between 1959 and 1965 indicated that within the 35-to-44-year-old age group 79 percent of those tested had antibodies against T. cruzi, and within the 5-to-14-year-old age group 15 percent were infected. Fortunately, these figures have dropped significantly since the 1970s because of the use of insecticides: within the group from birth to 9 years of age infection rates have lowered from 20.5 percent in 1959-1965 to 1.3 percent in 1980-1982; the rates have dropped from 28.4 percent to 2.7 percent in the group aged from 10 to 19 years. Levels of house infestation have also lowered considerablyfrom 73.2 percent of the huts and 31.1 percent of the houses at the beginning of the program in 1970 to 22.1 percent of the huts and 5.6 percent of the houses being infected in 1976 (Sequeda et al. 1986).
In Venezuela, initial success in the late 1970s led to diminishing insecticide use in the 1980s; it dropped from 74 percent coverage in 1980 to 11 percent in 1984 (Briceno-Leon 1990:29). Houses again became increasingly infested, in part because depletion of forests and sylvatic animals in Venezuela pressured triatomines to search for domestic sites for blood meals. This has been demonstrated in the Municipal Bergantin, Estado Anzoategui, where insecticides were used from 1970 until 1973, followed by three years without spraying insecticides. The rate of house infestation by triatomines increased from 2.8 percent to 11.4 percent, and hut
