The Kiss of Death

primary health care measures.

Fortunately for humans, many species of triatomines are sylvatic and feed on animals and birds; consequently, relatively few triatomine species feed on humans. Most of the species of triatomine bugs are prevalent in tropical and subtropical areas at altitudes between 200 and 1,500 meters (600-4,500 feet) above sea level, although eighteen species are found in near arctic biomes (T. patagonica is found in the Patagonian region of Argentina), twenty-three species in xerophytic forests, sixteen in desertic and semidesertic plains and plateaus (most notably the Altiplano, where T. infestans is found), and eleven in temperate foothills and valleys (Carcavallo 1987).

APPENDIX 8 Hosts for T. cruzi

Although triatomines are opportunistic blood feeders, the seven most important vector species (see Appendix 7: Vector species of T. cruzi in the Americas) show a preference for blood meals, with humans being the most desirable, then chickens and pigeons, and dogs and cats to a lesser degree. The nocturnal activity of cats saves them to a degree from these nocturnal predators. Guinea pigs are a delicacy to vinchucas in Bolivia and Peru, where Andeans traditionally raise them inside the kitchen. Guinea pigs have also been a factor for the spread of Chagas’ disease throughout Andean countries. Rats and mice play a lesser role in providing blood meals and a major role as predators of triatomine bugs, as are chickens and cats, thus somewhat suppressing triatomine populations.

An important ecological factor influencing transmission of Chagas’ disease is the association of triatomines with synanthropic animals (WHO 1991). Synanthropic animals are those animals that live around humans. They range from pets, livestock, and rodents to opossums, raccoons, foxes, deer, and other animals that, in part because of deforestation and encroachment upon forests, live close to humans. Because these animals serve as blood sources, they contribute considerably to maintaining or increasing population densities of domiciliary and peridomiciliary vectors. Animals also serve as vehicles to disperse triatomines to other parts of the world. The migratory wood stork (Mycteria americana), as one known example, carried Rhodnius prolixus from the north of South America to Central America and Mexico.

Epidemiologically, sylvatic and synanthropic animals serve as reservoir hosts for Trypanosoma cruzi. (Humans have become the principal hosts.) After Carlos Chagas (1909) found Trypanosoma cruzi in house-dwelling triatomines, Panstrongylus megistus, he discovered that the two important mammalian hosts in the domestic environment in the transmission cycles were humans and cats. Three years later, Chagas discovered infections in armadillos and recognized Panstrongylus geniculatus as the vector in this purely sylvatic cycle in armadillos. Subsequently, throughout the countries of Latin America, a wide variety of mammals and triatomine vectors have been identified as involved in the transmission cycle of T. cruzi and related flagellates. More than 150 species of wild and domestic mammals have been found to be reservoirs of T. cruzi (see WHO 1991: Annex 4 for list).

Certain animals are better reservoir hosts than others. Dogs, cats, and rodents are the prime reservoir hosts within the peridomestic arena, and opossums (Didelphis species) and armadillos within the sylvatic arena. T. cruzi infections in dogs have been reported from fifteen countries and infections in cats from seven, with great variability in infection rates (from 4.5 percent to 100 percent in dogs and from o.5 percent to 60.9 percent in cats). Dogs are important reservoir hosts due to their close contact with humans during the night, the age-independent persistence of parasitemia in dogs, and the possibility of congenital or lactogenic infection of dogs, as has been indicated by a study in Argentina. Guinea pigs are bred indoors in Bolivia and Peru, where high rates of infection have been reported (Bolivia, 10.5-61.1 percent; Peru, 19.2 percent [Gurtler et al. 1990; WHO 1991]).

Other domestic animalscattle, goats, pigs, donkeys, and horseshave rarely been found infected. They are not considered to play an important role as reservoirs because of their low population density, their less-close contact with humans, and their low rates of parasitemia (WHO 1991:25). Some species, such as goats and certain rats, appear to be able to eliminate the infection. Although they serve as blood meals, chickens, turkeys, ducks, and pigeons are not susceptible to T. cruzi infection (see Appendix 10: Immune Response). This is also true for all other birds as well as reptiles. Chickens are used in laboratories to blood feed sterile vinchucas that are used for xenodiagnosis. Veterinary researchers and animal environmentalists need to assess the considerable impact Chagas’ disease has upon domestic and sylvatic animals.

APPENDIX 9 Acute Chagas’ Disease

In 1909 Carlos Chagas diagnosed a child named Rita as having an acute attack of parasitemia caused by T. cruzi, and accurately described its symptoms:

Among the chief clinical symptoms of this child, whose fever had come on some eight or ten days before examination, were the following: axillary temperature 40°C (105°F) spleen enlarged and to be felt under the edge of the ribs; liver also enlarged; groups of peripheral lymph nodes swollen etc. Most noticeable was a generalized infiltration, more pronounced in the face, and which did not show the characteristics of renal oedema but rather of myxoedema. This last symptom, which I later found to be one of the most characteristic of the acute form of the disease, already then revealed some functional alternation of the thyroid gland, perhaps affected by the pathogenic action of the parasite (Chagas 1922).

Rita died three days later. The pathology of acute Chagas’ disease varies from a mild to a virulent infection. Some symptoms of acute Chagas’ are related to inflammation, which is one of the body’s defenses against T. cruzi and tissue damage, facilitating repair of the damage. Inflammation often includes fever, general malaise, and swelling and soreness of the lymph nodes and spleen, which contain large numbers of macrophages and T and B lymphocytes activated to combat antigens peculiar to T. cruzi. Inflammation’s redness and warmth result from the increased amount of blood in the area. Swelling results from more proteins and fluids escaping into the tissue (Schmidt and Roberts 1989:27).

Definite symptoms of acute Chagas’ are the ophthalmo-ganglial complex (Romafia’s sign) and chagoma of cutaneous inoculation, which occurs near the bite site in 90 percent of the people recently infected (WHO 1991; see Figure 4). However, Borda (1981) claims lesser percentages of from 1 to 3 percent. Romafia’s sign is not frequently found in Bolivia; if found, it is usually confused with an eye irritation. Appearing suddenly, Romafia’s sign is the swelling of the upper and lower eyelids in one eye. An infection occurs through the skin of the eyelid, developing into inflammation around the eye with edema and inflammation of the local lymph nodes. The swollen eyelids are firm to the touch, purple, and not painful. There can be an inflammation of the conjunctiva or the mucous membrane that lines the eyelids (Katz, Despommier, and Gwadz 1989:174). Moderate swelling extends to the same side of the face, which, if touched, is found to be hard. This swelling gradually disappears after a month. The duration and durability of Romafia’s sign set it apart from the swelling of other minor eye irritations.

Chagomas also appear at the infected bite sites of other parts of the body, especially on uncovered areashands, forearms, feet, calves, and legs. Nodule-like protrusions, chagomas are cutaneous tumors beneath the skin, resulting from the hardening of skin and subcutaneous cells. Chagomas are painful, firm, feverish, and abnormally red, which is due to capillary congestion in inflammations. When chagomas slowly disappear after a month, they leave a depigmentation, like a burn wound.

Acute infections also alter the cardiovascular system, with tachycardia (without correspondence to the