Seroepidemiological Investigation for Chagas Disease in Two Municipalities of Goiás, Brazil
Abstract
This study evaluated the risk of transmission of Chagas disease following implantation of the Brazilian National Health System (Sistema Único de Saúde – SUS) in two municipalities considered endemic risk areas. A seroepidemiological and entomological survey was conducted as part of the Triatoma infestans eradication program. According to a previous survey conducted in 1980, seroprevalence of Chagas disease was around 0.82% in São Luís dos Montes Belos and around 2.35% in Novo Brasil. In the present serological survey conducted in 303 schoolchildren born after the control phase in these regions, one of the children tested positive for the disease. In the 236 homes surveyed (150 in São Luís dos Montes Belos and 86 in Novo Brasil), all of which were infested by triatomine bugs, none of the triatomine bugs captured tested positive for Trypanosoma cruzi. Although Triatoma infestans is under control, there has been a considerable increase in secondary vectors such as Triatoma sordida; therefore, continuous epidemiological surveillance is fully justified within the current context of the SUS, and should be considered for inclusion as routine practice within the Family Health Program.
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Introduction
As part of a Chagas disease control program, the Brazilian Ministry of Health conducted a serological and triatomine survey throughout most of the country between 1975 and 1983. Data on the prevalence of the infection and on the distribution of its vectors were obtained. The areas in which the disease was endemic were identified, allowing control actions to be defined and prioritized [1, 2].
Chagas disease is an endemic disease caused by the protozoan parasite Trypanosoma cruzi, transmitted to humans and other animals by triatomine bugs. The condition is characterized by a chronic generalized infection. Chagas disease is found throughout the entire American continent from the southern United States to the south of Argentina [3]. Domestic transmission of the disease depends on the following factors: the vector must be present, it must be infected and it must have colonized human households. This situation results primarily from circumstances related to the environment, to man’seffect on the environment and to the attributes of the vector itself, all of which will end up favoring the presence of the vectors in households [4].
American trypanosomiasis, or Chagas disease, is the most prevalent zoonosis in Goiás, a Brazilian state that is considered a region at risk of vector transmission. Natural transmission has always been associated with close contact between humans and triatomine bugs, with rural populations being those most affected [5, 6].
Triatoma infestans was the principal household vector of Chagas disease in Brazil between 1975 and 1980 and it is now believed to be eradicated from the country. In 2006, the Pan American Health Organization/World Health Organization certified that, as a result of the Southern Cone Initiative against Chagas Disease, transmission by the principal household vector, Triatoma infestans, was halted [7].
From an epidemiological viewpoint, the state of Goiás ranked third with respect to the prevalence of Chagas disease in a nationwide survey conducted in 1980. In the municipality of São Luís dos Montes Belos, seroprevalence was around 0.82%, while in the municipality of Novo Brasil, the rate was around 2.35%. In Novo Brasil, a serological survey was conducted in children up to 10 years of age in 1980; however, no such survey was conducted in São Luis dos Montes Belos. At that time, the most prevalent species of triatomine bug were Triatoma sordida, Rhodnius neglectus, Panstrongylus diasi, Panstrongylus megistus and Triatoma pseudomaculata. [1].
Oliveira et al. reported that of 32,437 triatomine bugs examined in Goiás between 2000 and 2003, 276 (0.85%) tested positive for Trypanosoma cruzi. Of these 276 triatomine bugs, 234 (84.78%) were of the T. sordida species (50 intra-and 184 peridomestic) and 21 (7.61%) were of the Rhodnius neglectus species (18 intra-and 3 peridomestic) [4]. A triatomine survey conducted in April 2013 found six specimens of T. sordida infected by trypanosomatids in the town of Trombas (in northeastern Goiás), corresponding to a rate of infection of 0.6%. These trypanosomatids were morphologically similar to T. cruzi. [8].
Based on these previous serological and entomological data recorded by the regional offices of the National Health Foundation, this study aimed at evaluating the seroepidemiological and entomological patterns in towns considered areas of risk, although located within areas in which the transmission of Chagas disease has been controlled. The results of this study will be helpful when making decisions on the implementation of low-cost, effective and viable control measures, as well as the establishment of continuous entomological and epidemiological surveillance.
Conclusion
In conclusion, the measures required to control the transmission of Chagas disease consist of simultaneous seroepidemiological and entomological surveillance, continuous spraying of residual insecticides in endemic areas, and now the continuation and strengthening of health education by the Family Health Program.
In general, the data show how the control measures adopted up to the present time have been effective in controlling the disease; however, according to data obtained from the Epidemiological Surveillance Department of the Ministry of Health in December 2006, acute cases of the disease had been confirmed in Brazil.
Although the state of Goiás has been certified as free from T. infestans, the principal vector in previous years, the fact that other species of synanthropic triatomines have been captured that tested positive for T. cruzi (Chagas, 1909) is a warning that the natural transmission of Chagas disease continues in the state.
Further serological studies need to be conducted to increase the effectiveness of the program and its results, since in some municipalities no investigation has yet been carried out. Failure to conduct such studies may result in the non-identification of some areas in which Chagas disease continues to be transmitted, with the result that attack efforts to eradicate the disease may focus on the wrong strategic points in the state or even in the transfer of a large number of personnel to a region that is not so badly infested. It is vital to prioritize careful epidemiological surveillance, including the involvement of the population and local health authorities, and to have sufficient resources available to do so.