Mem Inst Oswaldo Cruz, Rio de Janeiro, 95(5) Sep/Oct 2000
Sylvatic Vectors Invading Houses and the Risk of Emergence of Cases of Chagas Disease in Salvador, State of Bahia, Northeast Brazil
Laboratório de Parasitologia/Entomologia, Centro de Pesquisas Gonçalo Moniz-Fiocruz,u00a0Rua Valdemar Falcão 121, 40295-001 Salvador, BA, Brasil
During the last twenty years, several adults ofu00a0Triatoma tibiamaculatau00a0infected withu00a0Trypanosoma cruziu00a0have been spontaneously caught by inhabitants, inside their houses in the new habitational district of Pituaçu of Salvador, Bahia. In this communication the authors call attention to the necessity of studies about the possibility of occurrence of new human cases of Chagas disease, to clarify the obscure origin of some positive blood donors in Salvador.
Chagas disease in the city of Salvador, Bahia has previously been a serious problem of public health there during many years, with high triatomine numbers showing natural infection by Trypanosoma cruzi (Chagas, 1909) being captured simultaneously with the registration of countless cases of autochthonous chagasic cardiopathy (Pondé 1946).
In those years, two triatomine species, Panstrongylus megistus (Burmeister, 1835) and Triatoma rubrofasciata (De Geer, 1773) were found to be naturally infected with T. cruzi and Trypanosoma conorhini (Donovan, 1909) (Gonçalves 1912).
After extensive surveys of triatomines inside houses in Salvador, starting from 1950 (Costa 1955, Aragão et al. 1955), a large scale campaign to combat those vectors with insecticides was begun in the city. Due to intense and frequent application of insecticides, the control of the triatomines was achieved, causing an accentuated reduction in their populations, in the main neighborhoods of the city (Leal et al. 1965). However, some outlying foci persisted, infested byP. megistus infected by T. cruzi, with transmission of the disease to several families that lived in the districts of Acupe de Brotas and Federação (Silva 1966). Finally, in 1974, in one of the last published surveys of triatomines carried out in the city of Salvador, 601 P. megistus and T. rubrofasciata were collected and examined among which 16% were infected by T. cruzi (Sherlock & Serafim 1974).
From 1996, we began to think about the possibility of occurrence of new human cases of Chagas disease in Salvador transmitted by triatomines, besides those 1.6% acquired by vertical transmission (Bittencourt 1999) or some others by blood transfusion (Bastos 1999), because some inhabitants spontaneously have brought to the Laboratory of Parasitology and Entomology of CPqGM-Fiocruz (Lapen) specimens of infected triatomines collected inside their dwellings. Our hypothesis was reinforced by the findings of positive xenodiagnosis of some authocthonous patients from Salvador, without connexions either with living in rural endemic areas, blood transfusions or congenital infection (unpublished data of Lapen) and results observed recently by Bastos (1999).
In the Table, we show the number and places of triatomines collected by the inhabitants. The specimens were identified as two Triatoma pseudo-maculata Correa & Spinola, 1964 and 11 specimens of the sylvatic Triatoma tibiamaculata(Pinto, 1926). This species is highly susceptible to infection with T. cruzi (Dias-Lima & Sherlock 1997). As noted in this Table, some of the specimens examined were infected with T. cruzi.
But we have to emphasize that besides the specimens mentioned in the Table, several other triatomines have been recently collected also by the inhabitants in other districts and around Salvador, such as Panstrongylus megistus, P. lutzi (Neiva & Pinto, 1923), P. geniculatus (Latreille, 1911) and Triatoma melanocephala Neiva & Pinto, 1923.
The Metropolitan Park of Pituaçu, 13°50'S/48º00'W, is a preserved area composed of Atlantic forest remains and secondary forest, located between the Avenue Luís Viana Filho - Paralela (inland) and the Avenue Octávio Mangabeira (in the littoral). This area still contains remnants of the original fauna that are being preserved by an official project. Nowadays, a great number of people reside in the proximities of the area of the Park. Urbanization groups, including habitational buildings, luxurious mansions, and precarious invasion dwellings penetrate the natural ecotopes and come into contact with the habitats of the wild vectors of T. cruzi.
T. tibiamaculata is a sylvatic species, that has as its main habitat the marsupial and rodent nests in bromelias (Sherlock 1979, Carcavallo et al. 1997).
Barrett et al. (1980) demonstrated the presence of T. tibiamaculata infected with T. cruzi Zymodeme 1, particularly in association with marsupials. In addition, T. cruzi Z1 was isolated from a woman with chronic Chagas disease, in the city of Nazaré das Farinhas, approximately 60 km from Salvador, suggesting that T. tibiamaculata can act as a vector of T. cruzi to humans.
Moura et al. (1969) registered a human case of chronic chagasic myocarditis acquired in a sylvatic enzootic focus in the littoral of Paraná and incriminated T. tibiamaculata, P. megistus and R. domesticus Neiva & Pinto, 1923, found naturally infected by T. cruzi, as the involved vectors.
Coura (1966) collected P. megistus and T. tibiamaculata infected with T. cruzi inside houses of Santa Tereza district, in Rio de Janeiro. But he did not believe in the possibility of the emergence of endemic Chagas disease, although he accepted the possibility of sporadic occurrence of human cases that could acquire the infection from the sylvatic zoonotic foci, where infected triatomine vectors and marsupials reservoirs coexisted.
The destruction of those ecotopes, can cause shortages and even the disappearance of the natural blood sources of the triatomines, resulting in the invasion of the human dwellings by those vectors, in search of blood meals on man, as it was observed, exposing the population to the risk of contracting Chagas disease.
Finally, we suggest the need for studies in the area of Pituaçu and adjoining neighbourhoods, to investigate the fauna of mammals and triatomines, with emphasis on the dimension of its populations and the degree of infection by trypanosomes. This would allow us to evaluate the risk to the inhabitants of this area, for infection with the etiological agent of Chagas disease.
Aragão JMB, Aguirre GH, Leal JM, Serafim E 1955. Contribuição ao conhecimento da distribuição geográfica dos triatomineos domiciliares e seus índices de infecção natural pelo Schizotrypanum cruzi, no Estado da Bahia. Rev Bras Malariol D Trop 7: 409-421.
Barrett TV, Hoff RH, Mott KE, Miles MA, Godfrey DG, Teixeira R, Almeida de Souza JÁ, Sherlock IA 1980. Epidemiological aspects of three Trypanosoma cruzi zymodemes in Bahia State, Brazil. Trans R Soc Trop Med Hyg 74: 84-90.
Bastos C 1999. Avaliação de Antígenos Recombinantes no Sorodiagnóstico da Infecção pelo Trypanosoma cruzi, em Salvador, Bahia, Universidade Federal da Bahia, Salvador, vi + 99 pp.
Bittencourt AL 1999. Transmissão vertical da doença de Chagas. In Z Brener, ZA Andrade, M Barral-Netto (eds),Trypanosama cruzi e Doença de Chagas, Guanabara Koogan, Rio de Janeiro, p. 16 -19.
Carcavallo RU, Rodriguez MEF, Salvatella R, Casas SIC, Sherlock lA, Galvão C, Rocha DS, Girón IG, Arocha MAO, Martineza A, Rosa JA, Canale DM, Farr TH, Barata JMS 1997. Habitats and related fauna. In RU Carcavallo, IG Giron, J Jurberg, H Lent (eds), Atlas of Chagas´ Disease Vectors in the America, Fiocruz, Rio de Janeiro, p. 561-600.
Costa AL 1955. Triatomineos e Tripanosomas por eles Veiculados em Zona Central na Cidade do Salvador - Bahia, Faculdade de Medicina da Bahia, Salvador, 81 pp.
Coura JR 1966. Contribuição ao estudo da doença de Chagas no Estado da Guanabara. Rev Bras Malariol D Trop18: 9-98.
Dias-Lima AG, Sherlock IA 1997. A presença de Triatoma tibiamaculata (Hemiptera: Reduviidae) e o risco de ocorrência da doença de Chagas, em Salvador, Bahia. Ann XV Cong Bras Parasitol, p. 45.
Gonçalves AE 1912. Contribuição para o Estudo do Mal de Chagas na Bahia, Faculdade de Medicina da Bahia, Salvador, 59 pp.
Leal JM, Sherlock IA, Serafim EM 1965. Observações sobre o combate aos triatomíneos domiciliários com BHC, em Salvador, Bahia. Rev Bras D Trop 17: 65-73.
Moura A, Luz E, Lima EC, Borba AM, Christian A, Veiga A 1969. A cardiopatia chagásica de origem silvestre no litoral paranaense. Estudo epidemiologico da área. Rev Inst Med Trop São Paulo 11: 408-424.
Pondé A 1946. A doença de Chagas na Bahia. Arquivos da Faculdade de Medicina da Bahia 1: 333-456.
Sherlock IA 1979. Vetores. In Z Brener, Z Andrade (eds), Trypanosoma cruzi e Doença de Chagas, Guanabara Koogan, Rio de Janeiro, p. 42-88.
Sherlock IA, Serafim EM 1974. Fauna triatominae do Estado da Bahia, Brasil.VI. Prevalência geográfica da infecção dos triatomíneos pelo T. cruzi. Rev Soc Bras Med Trop 8: 129-142.
Silva GR 1966. Doença de Chagas em Famílias de Duas Áreas Restritas da Cidade do Salvador, Thesis, Faculdade de Medicina da Bahia, Salvador, 143 pp.