Entomological aspects of Chagas' disease transmission in the domestic habitat, Argentina.

OBJECTIVE: To study the risk of Trypanosoma cruzi domestic transmission using an entomological index and to explore its relationship with household's characteristics and cultural aspects. METHODS: There were studied 158 households in an endemic area in Argentina. Each household was classified according to an entomological risk indicator (number of risky bites/human). A questionnaire was administered to evaluate risk factors among householders. RESULTS: Infested households showed a wide range of risk values (0 to 5 risky bites/human) with skewed distribution, a high frequency of lower values and few very high risk households. Of all collected Triatoma infestans, 44% had had human blood meals whereas 27% had had dogs or chickens blood meals. Having dogs and birds sharing room with humans increased the risk values. Tidy clean households had contributed significantly to lower risk values as a result of low vector density. The infested households showed a 24.3% correlation between time after insecticide application and the number of vectors. But there was no correlation between the time after insecticide application and T. infestans' infectivity. The statistical analysis showed a high correlation between current values of the entomological risk indicator and Trypanosoma cruzi seroprevalence in children. CONCLUSIONS: The risk of T. cruzi domestic transmission assessed using an entomological index show a correlation with children seroprevalence for Chagas' disease and householders' habits.

Entomological aspects of Chagas' disease transmission in the domestic habitat, Argentina

OBJETIVO: Estudiar el riesgo doméstico de transmisión de Trypanosoma cruzi por medio de un indicador entomológico y analizar su relación con características culturales y de las viviendas. MÉTODOS: Se estudiaron 158 casas en el área endémica argentina. Cada vivienda infestada se clasificó de acuerdo con un indicador entomológico de riesgo (número de picadas riesgosas/ humano). Mediante encuestas se evaluaron factores de riesgo asociados a la vivienda y habitos de los moradores. RESULTADOS: Las casas infestadas mostraron un rango amplio de valores de riesgo (0 a 5 picadas riesgosas/ humano). Se observó un gran número de viviendas con bajos valores de riesgo y pocas viviendas con valores elevados. El 44 por ciento de las Triatoma infestans colectadas estaban alimentadas sobre ser humano y el 27 por ciento sobre perro o gallina. Las viviendas donde perros y/o gallinas compartían la habitación humana, tuvieron valores de riesgo más elevados. Las viviendas ordenadas y limpias exhibieron bajos valores, debido a un escaso número de T. infestans. Se comprobó un 24.3 por ciento de correlación entre el tiempo transcurrido luego de aplicar insecticidas y el número de vectores en la vivienda. Sin embargo, no hubo correlación entre el tiempo post-rociado y la infectividad de T. infestans. Se observó correlación entre los valores del indicador entomológico y la seroprevalencia en niños. CONCLUSIONES: El riesgo de transmisión de T. cruzi en cada vivienda, medido a través de un indicador entomológico, se correlaciona positivamente con la prevalencia de seropositividad en niños y con hábitos de los moradores.

[Santa Fe triatomine bug detector. A high sensitivity and low cost design]. / Detector de vinchucas Santa Fe. Un diseño de alta sensibilidad y bajo costo.

In 1987, Wisnivesky et al. developed "Maria" sensor box (MSB) which was assayed by sanitary agents, during a surveillance phase. In 1987, this design, with the same strategy, was assayed in an area of Santa Fe Province where very good results were obtained. Due to the deterioration of the Primary Health Care system, Santa Fe's Control Programme has carried out a study with MSB used by the owners of the houses. Some difficulties related with the internal structure of MSB were detected. A new model named "Detector SANTA FE" (DSF) was designed in order to overcome these difficulties. The sensitivity and cost of both models were compared in this study. Evaluation of 63 households was carried out with 172 elements distributed in bedrooms, in Villa Minetti (9 de Julio Department). One MSB and one DSF were placed on the walls above the bed-heads, separated by 30 cm, 1.5 m from the floor. Results show that 22 houses were positive after the evaluations. Of those 22 positives, 7 were detected by both models simultaneously, 1 only by MSB and 14 by DSF alone. Sensitivity for MSB was 36% and for DSF was 95%. Regarding efficiency, MSB costs $3.00 per unit, while DSF costs $1.00 per unit. The conclusion of the study is that DSF is remarkably more sensitive and cheaper than MSB.

Result of a first step toward community-based surveillance of transmission of Chagas' disease with appropriate technology in rural areas.

The objective of this work was to develop an effective methodology for the surveillance of Chagas' disease vectors in rural areas. It was based on the use of sensor boxes and portable mini-pumps to be integrated into the regular health promotion activities of the Primary Health Care (PHC) agents. The proposed methodology involves a continuous passive intradomiciliary detection of triatomines by sensor boxes that are monitored quarterly by PHC agents. Insecticidal treatment of the houses was performed immediately after the detection of triatomines. The more conventional method of vertical surveillance involves a direct entomologic evaluation conducted by trained professionals. The entire house is searched and there is a mandated treatment of the positive houses. The results of the followups obtained in the county of Rio Hondo in Santiago del Estero Province during a 36-month evaluation period immediately following attack phase application of insecticides were analyzed. The initial high domiciliary and peridomiciliary infestations decreased abruptly after the insecticidal treatment in both areas. When the performances of both types of surveillance were compared, the PHC agent method showed a lower percentage of houses reinfested, with fewer triatomines in the former, and a decrease in their rate of Trypanosoma cruzi infection. Evaluations of reinfestations using the man/hour method and the senor box method showed the same sensitivity. A higher sensitivity for detection of low densities of vector populations was achieved using the sensor boxes. The cost of PHC agent/sensor boxes surveillance was five times lower than the classic one. The proposed strategy for the continuous surveillance of Chagas' disease vectors has demonstrated effectiveness, allows community participation, and seems suitable for large scale application.

The status of transmission of Trypanosoma cruzi in an endemic area of Argentina prior to control attempts, 1985.

A field survey of transmission of Trypanosoma cruzi was carried out in an area which had never been sprayed with insecticide. A population census, mapping and house classification, examination of insects in houses, and a human serological survey were performed. The entomological examination showed that 97% of the houses (433/445) were infested by Triatoma infestans and that 31% of the bugs examined were infected with T. cruzi. The level of infection, as well as the number of insects captured, had no apparent relationship with the type of house. Trypanosoma cruzi was found in 30% of the human population, and in 10% of children up to four years old. The rates of infection were significantly lower for inhabitants, especially children, living in 'urban' houses. The prevalence rate for the children did not correlate with the number of insects collected in the houses. The improvement of houses, outside the framework of an integrated control programme, had no obvious impact on the level of transmission. Nevertheless, the replacement of the original houses by houses with plastered walls and roofs of metal or cement resulted in a decrease in the prevalence of infection in children younger than four years of age. The community showed little confidence in sanitary precautions against Chagas' disease prior to the start of the survey.

Usefulness of serology for the evaluation of Trypanosoma cruzi transmission in endemic areas of Chagas' disease.

Thirteen communities from 7 Argentinian provinces were selected for the evaluation of serology as an indicator of transmission of Chagas disease. Of the communities appraised, 6 did not have a history of previous treatment with insecticides and 7 had received sporadic or continuous insecticide treatment. The inhabitants of 20% of the houses of each locality were studied by serology. The samples were obtained by finger pricking and 50 microliters of blood were mixed with 15 microliter of 50% glycerine solution in tissue culture media to be assayed by Indirect Hemagglutination and Indirect Immunofluorescence tests. In untreated areas, the prevalence of infection in infants 0-4 years old was 17.5%, reaching to over 22% for the 5-9 year old group, and to 33.3% in 10-14 year old individuals. The prevalence in treated and surveyed areas was 2.6% in 0-4 year old children, 5.4% in 5-9 year old and 6.2% in 10-14 year old youngsters. The differences between both areas were statistically significant (p less than 0.005). This study favors serology as a valid indicator for the evaluation of transmission of Chagas disease in rural areas.

Natural Trypanosoma cruzi infection in dogs of endemic areas of the Argentine Republic.

The population dynamics and the prevalence of chagasic infection of 352 dogs living in 108 rural houses infested by triatomines were studied. The region was divided into three sections according to increasing distances to an urban area. Each animal was identified by means of its particular characteristics and built, and its owners gave information about its habits. By means of xenodiagnosis, serology and ECG studies, prevalences of infection, parasitological-serological correlation, percentage of altered electrocardiographic outlines and percentage of houses with parasitemic dogs, were determined. The rural area showed a characteristic T. cruzi infection pattern and differences in the canine population parameters with respect to the other areas were observed: a higher proportion of puppies than adult dogs, a more sedentary population, higher prevalences of infection, as measured by xenodiagnosis, in dogs, and the highest proportion of bedroom insects infected with T. cruzi. It is assumed that the sedentary characteristics of the human population in that rural area impinge in the blood offer to the triatomine population, and the high percentage of parasitemic dogs of the area, contribute to the rise of "kissing bugs" infected with T. cruzi found in bedrooms.

Enrichment in spontaneous and complement dependent rosette forming cell populations using Ficoll-Hypaque gradient centrifugation.

Peripheral blood human T (TL) and B (BL) lymphocytes were separated by continuous Ficoll-Hypaque (FH) gradients. BL were found at the 1050 density interfase (70.5% EAC rosettes) with no TL (0% EAC rosettes); while at the 1068 density interfase there was an enrichment of TL (68% E rosettes) with very few BL (8.5% EAC rosettes).

[Alpha-hydroxy-acid dehydrogenase activity in Trypanosoma cruzi]. / Actividad alfa-hidoxi-acido dehidrogenasa en Trypanosoma cruzi.

Crude extracts of culture forms of epimastigotes, Tulahuén strain, showed activity to catalyze the reaction alpha-ketocid in equilibrium alpha-hydroxyacid linked to nicotinamide adenine dinucleotide (NAD). The enzyme utilizes the following substrates: alpha-ketobutyrate, alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, alpha-ketocaproate, alpha-ketoisocaproate, alpha-ketoglutarate and pyruvate. Kinetics for the three last substrates were of the Michaelian type. For the other ketocids, curves of activity against substrate concentration exhibited a bimodal character. Km and V values for alpha-ketoisocaproate were strikingly higher than those for the other substrates. Electrophoretic separation of extracts on polyacrylamide gel and specific staining showed a single zone of enzymatic activity with similar mobility for all the alpha-OH-acids tested. This finding would indicate that the same protein is responsible for the reaction. The observations presented demonstrate that culture forms of Trypanosoma cruzi possess the ability to interconvert pyruvate in equilibrium lactate and to regenerate NAD in anaerobiosis. Although the physiological significance of the reaction with alpha-ketoacids other than pyruvate is not known, similarity of substrate of substrate spectrum between alpha-OH-acid dehydrogenase from Trypanosoma cruzi and lactate dehydrogenase ioenzyme X from mammalian and avian spermatozoa is interesting. Perhaps activity of flagella requires analogous metabolic pathways.

Actividad alfa-hidoxi-acido dehidrogenasa en Trypanosoma cruzi / [Alpha-hydroxy-acid dehydrogenase activity in Trypanosoma cruzi]

Crude extracts of culture forms of epimastigotes, Tulahuén strain, showed activity to catalyze the reaction alpha-ketocid in equilibrium alpha-hydroxyacid linked to nicotinamide adenine dinucleotide (NAD). The enzyme utilizes the following substrates: alpha-ketobutyrate, alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, alpha-ketocaproate, alpha-ketoisocaproate, alpha-ketoglutarate and pyruvate. Kinetics for the three last substrates were of the Michaelian type. For the other ketocids, curves of activity against substrate concentration exhibited a bimodal character. Km and V values for alpha-ketoisocaproate were strikingly higher than those for the other substrates. Electrophoretic separation of extracts on polyacrylamide gel and specific staining showed a single zone of enzymatic activity with similar mobility for all the alpha-OH-acids tested. This finding would indicate that the same protein is responsible for the reaction. The observations presented demonstrate that culture forms of Trypanosoma cruzi possess the ability to interconvert pyruvate in equilibrium lactate and to regenerate NAD in anaerobiosis. Although the physiological significance of the reaction with alpha-ketoacids other than pyruvate is not known, similarity of substrate of substrate spectrum between alpha-OH-acid dehydrogenase from Trypanosoma cruzi and lactate dehydrogenase ioenzyme X from mammalian and avian spermatozoa is interesting. Perhaps activity of flagella requires analogous metabolic pathways.

Actividad alfa-hidoxi-acido dehidrogenasa en Trypanosoma cruzi. / [Alpha-hydroxy-acid dehydrogenase activity in Trypanosoma cruzi]

Crude extracts of culture forms of epimastigotes, Tulahuén strain, showed activity to catalyze the reaction alpha-ketocid in equilibrium alpha-hydroxyacid linked to nicotinamide adenine dinucleotide (NAD). The enzyme utilizes the following substrates: alpha-ketobutyrate, alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, alpha-ketocaproate, alpha-ketoisocaproate, alpha-ketoglutarate and pyruvate. Kinetics for the three last substrates were of the Michaelian type. For the other ketocids, curves of activity against substrate concentration exhibited a bimodal character. Km and V values for alpha-ketoisocaproate were strikingly higher than those for the other substrates. Electrophoretic separation of extracts on polyacrylamide gel and specific staining showed a single zone of enzymatic activity with similar mobility for all the alpha-OH-acids tested. This finding would indicate that the same protein is responsible for the reaction. The observations presented demonstrate that culture forms of Trypanosoma cruzi possess the ability to interconvert pyruvate in equilibrium lactate and to regenerate NAD in anaerobiosis. Although the physiological significance of the reaction with alpha-ketoacids other than pyruvate is not known, similarity of substrate of substrate spectrum between alpha-OH-acid dehydrogenase from Trypanosoma cruzi and lactate dehydrogenase ioenzyme X from mammalian and avian spermatozoa is interesting. Perhaps activity of flagella requires analogous metabolic pathways.