Surveillance of seroepidemiology and morbidity of Chagas disease in the Negro River, Brazilian Amazon

Chagas diseasein the Brazilian Amazon Region was previously regarded as an enzootic diseaseof wild animals, from the time when Chagas (1924) ⁴ confirmed that its cause wasTrypanosoma cruzi, a parasite found by Abhen-Athar in the common squirrelmonkey (Saimiri sciureus), in the state of Pará in 1922.Since then, a variety of mammal species (marsupials, bats, rodents, carnivores,edentates, and primates) native to the Amazon Region have been described asreservoirs of T. cruzi (Coura & Junqueira 2012). TableI shows the different species that form wild reservoirs for T. cruziin the Brazilian Amazon Region and the references for the respective authors.

Although at least16 species of wild triatomine exist in the Brazilian Amazon Region and 10 havebeen found to be infected with T. cruzi (Table II),no triatomines with adaptation to human homes have been detected in this region,except for Triatoma rubrofasciata, an uninfected species exclusivelyfound in port areas.

Valente et al.(1998) found Panstrongylus geniculatus in pigsties on the Island of Marajóand Luitgards-Moura et al. (2005) found Triatoma maculata in henhousesin agricultural colonisation areas in Roraima, peridomestic areas, and occasionallyhomes, but without adaptation. However, these situations indicate that the vectorsare present in close contact with humans, and thus there is a future risk ofadaptation.

Transmission ofChagas disease in the Brazilian Amazon Region may occur incidentally when humansinvade the wild ecotope, when vectors or marsupials invade human homes, or throughthe faeces and urine of triatomines or secretions from the scent glands of marsupials(Fig. 1). This occurs in the following situations: (a) contaminationof raw or cooked foods (açaí and others); (b) as a work-relatedillness of piassaba fibre gatherers (Fig. 2) and membersof their families (Fig. 3); and (c) occasionally when triatominescome into contact with people in their homes and/or in the surrounding areains search of food sources because of lack of reservoirs in enzootic areas (Couraet al. 1994, Coura 2013).

Between when Shawet al. (1969) described the first four acute autochthonous cases of Chagas diseasein Belém, Pará, and 1992, only 38 additional cases of this diseasehave been described in the Brazilian Amazon Region: 21 in Pará, ninein Amapá, four in Maranhão, three in Amazonas, and one in Acre.Since then, hundreds of cases have been described in acute outbreaks of Chagasdisease and serological surveys (Coura et al. 1995a ¹⁰ , Coura et al. 1995b ¹² , Coura et al. 1999, Coura et al. 2002a, b, Valente et al. 1999 ³³ , Valente et al. 2009, Pinto et al. 2008 ²⁸ , Brum-Soares et al. 2010 ³ , and several others).

The risks of Chagasdisease have become endemic in the Brazilian Amazon regions and depend on thefollowing factors: (1) the presence of 38 mammal species in six orders: Marsupialia(Didelphiomorphia), Chiroptera, Rodentia, Edentata (Xenarthra), Carnivora, and Primates; (2) the presence of 16 species of wild triatomines, of which 10 areinfected with T. cruzi, which penetrate homes or come into contact withpeople when enter forests to hunt or gather plant material (such as piassabafibres); (3) extensive deforestation involving the displacement of wild animals,which stimulates triatomines to seek blood to feed on, in peridomestic and domesticareas (pigsties, henhouses, and people living in these homes); (4) immigrationof people and animals with T. cruzi infection from endemic areas to theAmazon Region; and (5) lack of knowledge among people in the Amazon Region,regarding Chagas disease, its transmission mechanisms, and methods of avoidingit.

Studies of Chagasdisease in the Rio Negro microregion, Brazilian Amazon Region - Over thelast 20 years, from 1991 to 2011, we conducted five seroepidemiological andclinical studies of T. cruzi infection using samples from thepopulation of the Negro microregion in the Brazilian Amazon Region. The surveysincluded 7286 people living in the main settlement of the municipality of Barcelos,which is in this microregion. The people included in the sample ranged in agefrom children over the age of one year to elderly people over the age of 60years. Initially, one blood sample on filter paper was collected per familycluster among the population living in one in four of the inhabited houses (approximately25%), respectively in 1991, 1993, and 1997. In 2011, blood was collected fromthe entire population present that permitted collection. Screening tests byimmunofluorescence on filter paper was positive in 12.5% of the 710 blood samplescollected in 1991, 13.7% of the 658 samples in 1993, and 13.2% of the 886 samplesin 1997. However, when we applied indirect immunofluorescence, enzyme-linkedimmunosorbent assay (ELISA), and western blotting to the serum of the casesthat were positive on the filter paper, positivity was confirmed in only 2.8-5%of the 2254 samples collected in 1991, 1993, and 1997. This may be because ofan error in interpretation of the technique, in which cases were considered"positive" if immunofluorescent spots were present on the membrane rather thanover the entire parasite (Coura et al. 1995a ¹⁰ , Coura et al. 1995b ¹² , Coura et al. 1999 ⁷ , Coura et al. 2002a ⁶ , Coura et al. 2002b ⁸ , Coura et al. 2013 ¹¹ ). However,for the 4880 blood samples collected from the entire population present in 2011,correction of this error resulted in positivity in only 4.5% of cases (Couraet al. 2013). Similar results may be observed for riverine population of Pará(Valente et al. 1999 ³³ , Valente et al. 2009 ³² , Pinto et al. 2008 ²⁸ ).

A study of morbidityin which 38 seropositive cases were paired with the same number of age- andsex-matched seronegative cases showed abnormal electrocardiogram results in36.8% of seropositive cases and 21.5% of seronegative cases, while the echocardiogramresults were abnormal in 31.6% of seropositive cases and 18.4% of seronegativecases. Precordial pain and palpitations were observed more frequently in seropositivecases. Radiological examination of the oesophagus showed no differences betweenseropositive and seronegative cases (Brum-Soares et al. 2010 ³ ).

New seroepidemiologicalsurvey among piassaba fibre gatherers and members of their families - Anew seroepidemiological survey was conducted in 2015-2016, specifically amongpiassaba fibre (Leopoldinia piassaba) gatherers and members of theirfamilies who accompanied them. The locations surveyed were creeks of the Aracá,Curudurí, Demimi, Ererê, and Padauiri rivers, which are tributarieson the left bank of the Negro River, in the municipality of Barcelos (whichis 490 km from Manaus, the state capital of Amazonas); Barcelos-Cauréshighway; Preto River in Santa Isabel do Rio Negro; and Marié River, onthe right bank of the Negro River. Our operational base and field laboratoryfor this new survey was in the former hospital of the Salesian mission in themain settlement of the municipality of Barcelos. This location formed an extensionof our parasitic diseases laboratory at the Oswaldo Cruz Institute (Fiocruz).At this base, fieldwork materials (launches, tents, and other field materials)and bench materials (microscopes, centrifuges, glass cabinets, fridges, freezersand other equipment) were available. Fig. 4 shows the locationof the municipalities of Barcelos and Santa Isabel do Rio Negro, and Fig.5 shows the locations of some of the above mentioned rivers.

RESULTS

The questionnaireapplied revealed that 100% of the 482 patients (piassaba fibre gatherers andmembers of their families) recognised the triatomine Rhodnius brethesi,which they had observed in the piassaba plantations. Moreover, 81% said thatthey had seen these triatomines in their shacks and 79% said that they had beenbitten between one and ten times by these insects. Only 21% said that they didnot know whether they had ever been bitten by these insects. The 25 seropositivepatients (Table III) said that they had been bitten more thanten times by these insects.

Of the 482 piassabafibre gatherers and members of their families who underwent serological examination,only 273 attended our field base for detailed clinical examination and electrocardiogram.History-taking revealed complaints of palpitations, precordial pain, and dyspnoeaupon effort, and clinical examination revealed extrasystoles, tachycardia, andbradycardia. The presence of these conditions was independent of whether theindividuals showed positive results in serological examination. Electrocardiographicabnormalities were presented by the 273 patients who underwent this examination,among whom 22% showed conditions that were potentially attributable to Chagasdisease. However, only 25 of the 482 cases presented convergent positive serologicaltests (indirect immunofluorescence + ELISA) that were compatible with infectionby T. cruzi. Thus, the prevalence of serologically positive cases was5.2%. Among the 25 serological-positive cases, the average age was 48.4 years(range 17-82 years, median 45 years).

DISCUSSION

The factors determiningthe morbidity due to Chagas disease and its evolution in the Negro River microregion, state of Amazonas, relate directly to the population's intensity of exposureto wild vectors, particularly in piassaba plantations in the region, and typesof T. cruzi strain (Tc1 and Z3), which still show little adaptation tohumans. In studies conducted by Araujo (2000) ² of 10 T. cruzi strains(Tc1 and Z3) in this region (two isolated from humans, two from marsupials,and six from R. brethesi), it was shown that these strains had low-virulencecharacteristics. Analysis of these parameters revealed that the prevalence ofT. cruzi infection and morbidity of Chagas disease in this region weredirectly related to the population's intensity of exposure. Exposure resultedfrom the working conditions of piassaba fire gatherers and possibly from thetype of wild strain of T. cruzi circulating in the area, as demonstratedby Albajar et al. (2003). These authors reported only two fatal cases of Chagas disease in this area, and Xavier et al. (2006) reported three severe cases ofdisease leading to death shortly afterwards. The cases described by both authorswere of piassaba gatherers subjected to frequent exposure over many years ofworking in the plantations.

R. brethesi,referred to as "piassaba louse" by the local population, has a specific nichehabitat in the palm species L. piassaba. This species contacts piassabafibre gatherers in the shacks set up close to the piassaba plantations. Transmissionof T. cruzi generally occurs through invasion of the shacks by triatominesat night, which search for blood meals from the piassaba fibre gatherers andmembers of their families when the reservoirs in their natural niche in thepalm trees are absent. Occasionally, triatomines attack the population outsideof their shacks in search of food.

In the variousstudies we conducted at many piassaba plantations in the Negro River region,we have collected marsupials, primates, rodents, carnivores, bats, and triatomines(R. brethesi) infected with T. cruzi to varying degrees. Thiscollection includes 240 animals from five species with different percentagesof T. cruzi (mean of 22.7%) and 949 triatomines (R. brethesi),among which only 19 were infected to give a rate of only 2%. Of the total of1189 animals and triatomines, 73 were infected with T. cruzi, and thusthe average was 6.14%. Based on these differences, triatomines use differentmethods for sucking blood from certain animal species or T. cruzi hassome difficulty in developing in some blood, leading to a low infection rateof only 2%.

Comments- (i) Chagas disease in the Negro River microregion, state of Amazonas, is awild enzootic disease in which the vectors transmit T. cruzi to piassabafibre gatherers and members of their families, predominantly in their shacks;(ii) the dominant vector for T. cruzi in this microregion is R. brethesi,which has a specific niche habitat in piassaba palm (L. piassaba), fromwhere the adult vectors fly out to the shacks of the piassaba fibre gatherersand members of their families to feed if no animals are present or if it isimpossible to suck the animals' blood; (iii) methods for preventing transmissionof Chagas disease in this region are very limited. Piassaba gatherers may beable to spray the piassaba palm trees and their shacks (to which the vectorsmigrate) with insecticide; (iv) use of mosquito nets impregnated with insecticide,for the piassaba gatherers' hammocks, may be recommendable. However, consideringthe heat in this area, it seems unlikely that a mosquito net would be used properly,i.e. as recommended for combating malaria in some areas; (v) finally, to decreasethe rate of this disease, we recommend the following measures, in addition tothose stated above: (a) to implement specific courses aimed at elementary schoolteachers who can provide guidance; (b) to train laboratory technicians and endemic-diseaseagents in early diagnoses of this disease among individuals in the acute phaseand provide immediate treatment; and (c) to provide information to local doctors,nurses, and healthcare agents to enable treatment of acute cases and referralof chronic cases of Chagas disease to regional hospitals.