Treatment of Chagas’ Disease

Dr. Ciro Figaroa, a medical doctor in Tarija, Bolivia, administers the following dosages of nifurtimox for acute Chagas’ disease: for children, 15 to 20 milligrams per kilo of weight in four doses per day for 90 days; for adults, 8 to 10 milligrams per kilo of weight for 120 days. Figaroa claims that he has cured Chagas’ disease in the acute phase but is unable to do this once patients have passed the acute stage. In Sucre, doctors recommend Radanil (Roche’s benznidazole product) in the following dosage: 7 milligrams per kilo of weight three times a day for four weeks. The cost for Radanil for an average‑size adult for one month is $340 Bolivian (or U.S. $70), a month’s wage for the average Bolivian.

An advantage of the acute phase of Chagas’ disease is that its symptoms signal a point when it can be treated. Asymptomatic patients may realize they are infected only at the chronic stage, when cardiac and gastrointestinal damage is pronounced. There currently is no adequate treatment for the chronic phase (for future possibilities see Urbina et al. 1996). Since the trypanocidal drugs currently available are effective during the acute period of the disease, it is important to diagnose earlier infections as well as to distinguish recent infections from older infections. New tools for the serodiagnosis of Chagas’ disease have proven to have great diagnostic potential in distinguishing different stages of the disease (see Frasch and Reyes 1990: 137‑41).

Chemotherapy treatment of the disease is not completely satisfactory for reasons already discussed in Chapter 3. Nifurtimox and benznidazole have serious adverse effects and yet do not destroy all the parasites, which soon repopulate the body. Their therapeutic efficacy depends upon variations in parasite virulence and variations in the human response to infection as they relate to a particular chemotherapeutic strategy.

In Bolivia and other Andean countries, the inadequacy of chemotherapy is related to the fact that trypanosomiasis generally is a disease of rural subsistence farmers in developing areas. Here, medical service is usually inadequate because of the inequitable distribution of health resources in favor of urban centers. To be useful in this environment, a drug must be inexpensive, have a long shelf‑life without refrigeration, and be able to be administered by paramedics orally without side effects.[15]

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, Schmuñis 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.