INDEX OF COMMUNITY AND HOUSE INFESTATION IN BOLIVIA

(adapted from Valencia 1990a:36)

Within Stratum B¹, communities from 1,000 to 4,999 inhabitants, the infestation rate was 27.71 percent, which was close to the national average. These communities are market, provincial, and regional centers scattered throughout the plains, valleys, and mountains of Bolivia. Some communities have pre‑Columbian origins, while others were founded during the colonial period as reducciones and pueblos to administer the colonies. Spanish conquistadores attempted to control Andeans by clustering them into religious indoctrination centers (reducciones ) and municipal centers (pueblos ). These houses are constructed of adobe, with thatched roofs and dirt or brick floors, and many stand as architectural monuments to another generation. They have become centers for triatomines. Rarely does one find that the vecinos (villagers from 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 (Muñoz 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.