The eco-epidemiology of Triatoma infestans in the temperate Monte Desert ecoregion of mid-western Argentina

BACKGROUND The eco-epidemiological status of Chagas disease in the Monte Desert ecoregion of western Argentina is largely unknown. We investigated the environmental and socio-demographic determinants of house infestation with Triatoma infestans, bug abundance, vector infection with Trypanosoma cruzi and host-feeding sources in a well-defined rural area of Lavalle Department in the Mendoza province. METHODS Technical personnel inspected 198 houses for evidence of infestation with T. infestans, and the 76 houses included in the current study were re-inspected. In parallel with the vector survey, an environmental and socio-demographic survey was also conducted. Univariate risk factor analysis for domiciliary infestation was carried out using Firth penalised logistic regression. We fitted generalised linear models for house infestation and bug abundance. Blood meals were tested with a direct ELISA assay, and T. cruzi infection was determined using a hot-start polymerase chain reaction (PCR) targeting the kinetoplast minicircle (kDNA-PCR). FINDINGS The households studied included an aged population living in precarious houses whose main economic activities included goat husbandry. T. infestans was found in 21.2% of 198 houses and in 55.3% of the 76 re-inspected houses. Peridomestic habitats exhibited higher infestation rates and bug abundances than did domiciles, and goat corrals showed high levels of infestation. The main host-feeding sources were goats. Vector infection was present in 10.2% of domiciles and 3.2% of peridomiciles. Generalised linear models showed that peridomestic infestation was positively and significantly associated with the presence of mud walls and the abundance of chickens and goats, and bug abundance increased with the number of all hosts except rabbits. MAIN CONCLUSIONS We highlight the relative importance of specific peridomestic structures (i.e., goat corrals and chicken coops) associated with construction materials and host abundance as sources of persistent bug infestation driving domestic colonisation. Environmental management strategies framed in a community-based programme combined with improved insecticide spraying and sustained vector surveillance are needed to effectively suppress local T. infestans populations.

The peri-urban interface and house infestation with Triatoma infestans in the Argentine Chaco: an underreported process?

Peri-urban infestations with triatomine bugs, their sources and their dynamics have rarely been investigated. Here, we corroborated the reported occurrence of Triatoma infestans in a peri-urban area and in neighbouring rural houses in Pampa del Indio, in the Argentine Chaco, and identified its putative sources using spatial analysis and demographic questionnaires. Peri-urban householders reported that 10% of their premises had triatomines, whereas T. infestans was collected by timed manual searches or community-based surveillance in only nine (3%) houses. Trypanosoma cruzi-infected T. infestans and Triatoma sordida were collected indoors only in peri-urban houses and were infected with TcV and TcI, respectively. The triatomines fed on chickens, cats and humans. Peri-urban infestations were most frequent in a squatter settlement and particularly within the recently built mud houses of rural immigrants, with large-sized households, more dogs and cats and more crowding. Several of the observed infestations were most likely associated with passive bug transport from other sources and with active bug dispersal from neighbouring foci. Thus, the households in the squatter settlement were at a greater risk of bug invasion and colonisation. In sum, the incipient process of domestic colonisation and transmission, along with persistent rural-to-urban migratory flows and unplanned urbanisation, indicate the need for active vector surveillance and control actions at the peri-urban interface of the Gran Chaco.

Chronic Chagas disease: PCR-xenodiagnosis without previous microscopic observation is a useful tool to detect viable Trypanosoma cruzi

We evaluate the elimination of the microscopic stage of conventional xenodiagnosis (XD) to optimize the parasitological diagnosis of Trypanosoma cruzi in chronic Chagas disease. To this purpose we applied under informed consent two XD cages to 150 Chilean chronic chagasic patients. The fecal samples (FS) of the triatomines at 30, 60 and 90 days post feeding were divided into two parts: in one a microscopic search for mobile trypomastigote and/or epimastigote forms was performed. In the other part, DNA extraction-purification for PCR directed to the conserved region of kDNA minicircles of trypanosomes (PCR-XD), without previous microscopic observation was done. An XD was considered positive when at least one mobile T. cruzi parasite in any one of three periods of incubation was observed, whereas PCR-XD was considered positive when the 330 bp band specific for T. cruzi was detected. 25 of 26 cases with positive conventional XD were PCR-XD positive (concordance 96.2%), whereas 85 of 124 cases with negative conventional XD were positive by PCR-XD (68.5%). Human chromosome 12 detected by Real-time PCR used as exogenous internal control of PCR-XD reaction allowed to discounting of PCR inhibition and false negative in 40 cases with negative PCR-XD. Conclusion: PCR-XD performed without previous microscopic observation is a useful tool for detection of viable parasites with higher efficiency then conventional XD.

Urban transmission of Chagas disease in Cochabamba, Bolivia

Chagas disease is a major public health problem in Bolivia. In the city of Cochabamba, 58 percent of the population lives in peripheral urban districts ("popular zones") where the infection prevalence is extremely high. From 1995 to 1999, we studied the demographics of Chagas infections in children from five to 13 years old (n = 2218) from the South zone (SZ) and North zone (NZ) districts, which differ in social, environmental, and agricultural conditions. Information gathered from these districts demonstrates qualitative and quantitative evidence for the active transmission of Trypanosoma cruzi in urban Cochabamba. Seropositivity was high in both zones (25 percent in SZ and 19 percent in NZ). We observed a high risk of infection in children from five to nine years old in SZ, but in NZ, a higher risk occurred in children aged 10-13, with odds ratio for infection three times higher in NZ than in SZ. This difference was not due to triatomine density, since more than 1,000 Triatoma infestans were captured in both zones, but was possibly secondary to the vector infection rate (79 percent in SZ and 37 percent in NZ). Electrocardiogram abnormalities were found to be prevalent in children and pre-adolescents (SZ = 40 percent, NZ = 17 percent), indicating that under continuous exposure to infection and re-infection, a severe form of the disease may develop early in life. This work demonstrates that T. cruzi infection should also be considered an urban health problem and is not restricted to the rural areas and small villages of Bolivia.

Ticks, ivermectin, and experimental Chagas disease

Following an infestation of dogticks in kennels housing dogs used for long-term studies of the pathogenesis of Chagas disease, we examined the effect of ivermectin treatment on the dogs, ticks, trypanosome parasites, and also on triatomine vectors of Chagas disease. Ivermectin treatment was highly effective in eliminating the ticks, but showed no apparent effect on the dogs nor on their trypanosome infection. Triatominae fed on the dogs soon after ivermectin treatment showed high mortality, but this effect quickly declined for bugs fed at successive intervals after treatment. In conclusion, although ivermectin treatment may have a transient effect on peridomestic populations of Triatominae, it is not the treatment of choice for this situation. The study also showed that although the dogticks could become infected with Trypanosoma cruzi, this only occurred when feeding on dogs in the acute phase of infection, and there was no evidence of subsequent parasite development in the ticks.

Xenodiagnóstico na doença de Chagas crônica: I - Sensibilidade de Panstrongylus megistus e Triatoma infestans / Xenodiagnosis in chronic Chagas' disease: I - Sensibility of Panstrongylus megistus and Triatoma infestans

From January 1986 to February 1994, 563 xenodiagnosis (XD) were applied in 563 chronic chagasic patients from different areas of Brazil; 292 were women and 271 were men between 6 and 89 years (average: 41.4 +/- 14.7 years). To each XD 40 nymphs on the 4th stage were used: 20 from Panstrongylus megistus (Pm) and 20 from Triatoma infestans (Ti) in fast, during at least 14 days. The exam in each nymph was made 45 days after being applied on the patient, by observation in optical microscopy of the drugs and/or the grinded from the digestive tube. The results are: a) 205 (36.4 per cent) positive XD, including 85 (15.1 per cent) due only nymphs of Pm, 44 (7.8 per cent) Ti and 76 (13.5 per cent) Pm and Ti; b) positively in 4.9 per cent of the nymphs from Pm and in 3.0 per cent of the Ti nymphs examined. These results' analysis showed that the Pm nymphs were more sensitive that Ti's ones to the infection by Trypanosoma cruzi, increasing considerably the xenopositivity, independently from birthplace, sex or age of the patients. These results point out that to increase the efficacy of XD in chronic Chagas' disease, the exam must have more than a species of triatomine with different sensibilities to the T. cruzi infection, and in case of using one species on XD, Pm must substitute Ti.

Epidemiología de la enfermedad de Chagas en Chile: frecuencia de infección humana por trypanosoma cruzi por grupos de edad y por regiones / Epidemiology of Chagas's disease in Chile: frequency of trypanosoma cruzi human infection by age groups and regions

Chagas's disease is endemic in rural-periurban sections of the northern half of Chile which includes the first seven political-administrative regions of the country (18º30'-34º36' South lat.). Data concerning to the results of an indirect hemagglutination test for Chagas's disease performed to 15,418 rural-periurban and 45,119 urban inhabitants from the chagasic endemic regions are presented migrations from rural-periurban to urban areas have contributed to the dissemination of trypanosoma cruzi infection. General rates of infection for rural-periurban (r-p) and urban (u) sections were 16,7 for percent and 1,9 for percent respectively. The higher prevalence rates were detected in region III with 27,2 for percent (r-p) and 3,9 (u) and Region IV with 24,7 for percent (r-p) and 3,5 for percent (u), while the lower prevalence rates corresponded to Region VI with 7,0 for percent (r-p) and 0,8 for percent (u). Serological positivity increased parallelly with age in all regions

Epidemiología de la enfermedad de Chagas en la provincia de Entre Ríos, Argentina / Epidemiology of the chases disease in Entre Rios province, Argentina

El presente trabajo resume una labor de evaluación epidemiológica para la enfermedad de Chagas, en la Provincia de Entre Ríos y en especial en su Departamento Uruguay, que se extendiera por más de 12 años. El rango etáreo de la muestra de población general estudiada fue de 5 a 65 años, y también se realizaron estudios sobre conscriptos entrerrianos, de entre 18 y 20 años (media de 19 años) y dadores de sangre del Departamento Uruguay (media 35 años). Excepto en estas dos últimas muestras poblacionales, en todas las demás se efectuaron visitas domiciliarias para la extracción de muestras, con la realización de un completo relevamiento de indicadores socioeconómicos, sanitarios, educativos, ambientales y culturales, y la inspección ocular de la vivienda en búsqueda de vectores y su grado de infestación. La presencia de anticuerpos para T. cruzi fue estudiada mediante cuatro técnicas serológicas (Hemoaglutinación indirecta; Aglutinación directa, Test de inmunofluorescencia indirecta y ELISA), y los individuos con serología positiva, sometidos a un estudio clínico y cardiológico. Los resultados indican una prevalencia provincial actual media de 4,6 por ciento de serología positiva, con una tendencia decreciente, al parecer relacionada con las campañas de fumigación, control de bancos de sangre y educación sanitaria, con un rango de 3,5 por ciento en el Dpto. Uruguay hasta un 6,8 por ciento en el Departamento Gualeguay. Al parecer, una asociación positiva se presenta entre seropositividad y baja estructura educacional, indisponibilidad de agua corriente, vivienda anterior precaria, techo de la vivienda anterior de paja o cartón y la presencia en las cercanías de criaderos de pollos parrilleros y gallinas ponedoras, en tanto que ninguna diferencia resultó significativa entre seropositivos y seronegativos para los indicadores de las siguientes variables del contexto de la población estudiada: conformación del núcleo familiar, tipo de baño, recolección de basura, tenencia de animales domésticos, ocupación laboral, disponibilidad de energía eléctrica y corrales aledaños. Sobre la base de los estudios cardiológicos, resultó bastante menor que la informada en la bibliografía, la asociación entre cardiopatologías por ECG de reposo y seropositividad, y ninguna en los 1.620 monitoreados por ECG de los 18.881 pre-conscriptos estudiados, lo que reafirma cuestionamientos recientes acerca de la utilidad de dicha técnica de diagnóstico cardiopatológico, para inducir una relación de cardiopatías con la infectación chagásica

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease: 4. The reflection of parasite stock in the responsiveness of different vector species to chronic infection with different Trypanosoma cruzi..

Estudos anteriores (1982, 1987) enfatizaram a superioridade das espécies vetoras silvestres às domiciliadas, como agentes do xenodiagnòstico nas infecçöes agudas e crônicas pelo isolado Y do T.cruzi. Os dados atuais estabeleceram a generalidade deste fenômeno. Por exemplo, a proporçäo de positivos nas infecçöes por "Säo Felipe" variou de 82,5 por cento a 98,3 por cento nos vetores silvestres, caindo para 42,5 por cento a 71,3 por cento em espécies domiciliadas. Ficou claro o envolvimento do isolado do T.cruzi na resposta do vetor à infecçäo crônica por T.cruzi. Por exemplo, os índices de infectividade produzidos por "Berenice", "Y", "FL" e "CL" variaram de 56,3 por cento a 88,3 por cento em P.megistus e de 28,8 por cento a 58,8 por cento em T.sordida. Sendo a resposta das mesmas espécies vetoras às infecçöes agudas pelos mesmos isolados altamente uniformes, aproximando-se a 100 por cento, sugere-se que a grande carga parasitária nas infecçöes agudas oculta as diferenças interespecíficas existentes entre os isolados do T.cruzi. A análise dos dados obtidos levou a especular que resultados adicionais de mais isolados permitiriam associar os índices de infectividade, produzidos por diferentes isolados do T.cruzi, aos perfis isoenzimáticos revelados por esses

Parasitemia em pacientes chagásicos crônicos avaliada pelo índice de triatomíneos infectados no xenodiagnóstico / Parasitemia in chronic chagasic patients evaluated by index of infected Triatoma in xenodiagnosis

Como parte de um estudo pré-terapêutico da infecçäo chagásica crônica a parasitemia de 206 pacientes (85 homens e 121 mulheres, com idades de 7 a 80 anos, média de 37,4 ñ 14,6) do município de Virgem la Lapa, Minas Gerais, foi avaliada pelo índice de ninfas de triatomíneos infectadas nos xenodiagnósticos aplicados. Cada paciente foi submetido a três exames no período de 12 meses. Em cada exame foram aplicadas 40 ninfas de 3§ ou 4§ estádios de Triatoma infestans. A parasitemia de cada paciente foi classificada arbitrariamente, de acordo com o percentual de ninfas positivas no total de examinadas nos três xenos, em: näo detectada - todas as ninfas negativas; baixa - quando o valor era maior que zero ou até igual a 2,0%; média - quando maior que 2,0% ou até igual a 7,0%; e alta - quando era maior que 7,0%. Com esses critérios a parasitemia näo foi detectada em 105 (51,0%) pacientes, foi baixa em 55 (26,7%), média em 27 (13,1%) e al;ta em 19 (9,2%). Näo houve diferença nos níveis da parasitemia em relaçäo ao sexo dos pacientes, mas em relaçäo aos grupos etários foi maior a freqüência da parasitemia baixa no grupo de 60 ou mais anos. A parasitemia alta foi mais freqüente no grupo de pacientes com cardipatia crônica chagásica. A "parasitemia persistente" (todos os xenopositivos) foi observada em todos os pacientes com parasitemia alta, em 22,2% dos que apresentaram parasitemia média e em nenhum com parasitemia baixa

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with chagas' disease: 2. Attempts to upgrade the reliability and the efficacy of xenodiagnosis in chronic chagas' disease

Assumindo que a otimizaçäo do xenodiagnóstico poderia apresentar um passo primordial na estratégia que visa a minimizaçäo de casos falso negativos, tanto nos levantamentos longitudinais da doença de Chagas, quanto na sua quimioterapia, apresentamos um estudo sobre a reconstruçäo do xenodiagnóstico, dando maior ênfase à dinâmica da populaçäo no xenodiagnóstico. Conseqüentemente, com o objetivo de levantar a credibilidade do xenodiagnóstico foram tomadas as seguintes medidas: 1. A densidade da populaçäo parasitária que em si näo é um objetivo de investigaçöes, mas retratando nitidamente a evoluçäo e multiplicaçäo do parasita, foi incorporada na triagem de insetos para o xenodiagnóstico. 2. Assumindo que a realimentaçäo do inseto infectado é capaz de triplicar a densidade da populaçäo parasitária, este foi realimentado de duas em duas semanas em galinhas. 3. Na avaliaçäo da resposta do inseto a infecçäo por T. cruzi foi medida no tubo digestivo completo no lugar da de fezes obtidas por compressäo do barbeiro. 4. Sendo a densidade da populaçäo parasitária nos primeiros 15 dias após a infecçäo bem baixa, porém crescendo rapidamente nos 30 dias posteriores, adotou-se o intervalo de 45 dias para o exame do inseto alimentado no hospedeiro com a doença crônica. A eficácia do xenodiagnóstico parece estar associada com o inseto utilizado como seu agente. Das 9 espécies vetoras exploradas neste sentido o inseto da espécie Panstrongylus megistus mostrou-se o mais promissor, devido ao seu elevado índice de infectividade (91.2%), estando a maioria destes (61.9%) com elevadas cargas parasitárias. Destaca-se também este inseto pela sua extraordinária capacidade de sustentar a rápida evoluçäo e boa multiplicaçäo de poucos parasitas ingeridos do hospedeiro na fase crônica. Isto está bem ilustrado na comparaçäo do seu índice de positivos de 91.2% com este de 96.4% encontrado entre os insetos alimentados no mesmo hospedeiro com a infecçäo aguda, quando o numero estimado de parasitas na sua circulaçäo foi de 12.3 x 10**3 por ocasiäo do xenodiagnóstico

Contribución al estudio de la enfermedad de Chagas en la provincia de Entre Ríos / Contribution to study of Chagas' disease in the province of Entre Rios

Se procura facilitar la tarea de los laboratorios bioquímicos en la realización de técnicas de investigación parasitológica y serológica, reseñándose antecedentes de estudios anteriores de la provincia de Entre Ríos, describiéndose las investigaciones en triatominos, parasitológicas y serológicas realizadas en esa provincia. Se caracterizan los vectores de la enfermedad de Chagas (Triatoma infestans): organización externa, hábitat, alimentación, ciclo evolutivo y campaña de desinsectización a seguir contra estos vectores. También se caracteriza al Trypanosoma cruzi, y su ciclo evolutivo en mamíferos y triatominos. Se describen métodos y técnicas: de diagnóstico parasitológico (por gota fresca, microhematocrito, Strout, por hemocultivo, xenodiagnóstico e inoculación en animales sensibles) y, de diagnóstico serológico (ELISA, test de Aglutinación Directa, de Hemoglutinación Indirecta - cualitativa y semicualitativa-, test de inmunofluorescencia). Se formulan recomendaciones para el diagnóstico de laboratório de la enfermedad de Chagas en el período agudo y crónico, en embarazadas, recién nacidos, y en Chagas post-transfusional. Se detallan el esquema de funcionamiento y la estructura del servicio bioquímico y del equipo de diagnóstico y tratamiento del Hospital "Justo José de Urquiza" (Concepción del Uruguay, Entre Ríos). Finalmente, se informa sobre la estadística serológica realizada, discutiéndose las técnicas diagnósticas utilizadas