Geographical Variation of Deltamethrin Susceptibility of Triatoma infestans (Hemiptera: Reduviidae) in Argentina With Emphasis on a Resistant Focus in the Gran Chaco.

Chagas disease is one of the most important parasitic infections in Latin America. The main vector of the protozoan Trypanosoma cruzi in America is Triatoma infestans, a blood-sucking triatomine bug who is widely distributed in the Gran Chaco ecoregion. Control programs in endemic countries are focused in the elimination of triatomine vectors with pyrethroid insecticides. However, chemical control has failed in the Gran Chaco over the last two decades because of several factors. Previous studies have reported the evolution of different levels of resistance to deltamethrin in Tri. infestans Recently, very high resistance has been found in the central area of the Argentine Gran Chaco. However, the origin and the extension of this remarkably resistant focus remain unknown. The aim of this study was to evaluate the geographical variation of deltamethrin susceptibility of Tri. infestans in different endemic provinces of Argentina, with emphasis in the center of the Argentine Gran Chaco ecoregion where this main vector has not been reduced. Populations of Mendoza, San Juan, Santiago del Estero, and Tucumán provinces were all susceptible. Resistant populations were only detected in the province of Chaco, where a mosaic resistant focus was described at the Güemes Department. It was characterized into three pyrethroid resistance categories: susceptible, low, and highly resistant populations. We found the populations with the highest resistance levels to deltamethrin, with resistant ratios over 1000.

Fenitrothion: an alternative insecticide for the control of deltamethrin-resistant populations of Triatoma infestans in northern Argentina.

Deltamethrin-based campaigns to control Triatoma infestans (Klug) (Hemiptera: Reduviidae) have decreased in success as a result of the development of insecticide resistance. We compared the in vitro effects of the pyrethroid deltamethrin and two doses of the organophosphate fenitrothion, presented on different materials, on T. infestans from La Esperanza, Argentina. Laboratory tests demonstrated a decrease in susceptibility to deltamethrin in the field population [LD50 : 30.32 nanograms per insect (ng/i)] compared with the reference population (LD50 : 0.13 ng/i), giving a high resistance ratio of 233.42. By contrast, similar susceptibility to fenitrothion was assessed in both the field and reference populations (LD50 : 21.65 ng/i and 21.38 ng/i, respectively). The effectiveness of the formulated insecticides varied according to the surfaces to which they were applied. The application of fenitrothion formulations to glass or brick resulted in mortality of 90-100%. The application of fenitrothion formulations to wood or mud caused mortality in the range of 6.7-56.7%. Resistant insects presented low mortality when exposed to the deltamethrin formulation and high mortality when exposed to fenitrothion formulations. Moreover, the insecticides demonstrated residual activity only when applied to glass. The present work demonstrates that fenitrothion is an alternative to pyrethroids for the management of deltamethrin-resistant insects in La Esperanza. However, this effectiveness is not sustained over time.

Rheological analysis and measurement of neutrophil indentation.

Aspects of neutrophil mechanical behavior relevant to the formation of adhesive contacts were assessed by measuring the dependence of the contact area between the cell and a spherical substrate under controlled loading. Micropipettes were used to bring neutrophils into contact with spherical beads under known forces, and the corresponding contact area was measured over time. The neutrophil was modeled as a viscous liquid drop with a constant cortical tension. Both the equilibrium state and the dynamics of the approach to equilibrium were examined. The equilibrium contact area increased monotonically with force in a manner consistent with a cell cortical tension of 16-24 pN/microm. The dynamic response matched predictions based on a model of the cell as a growing drop using published values for the effective viscosity of the cell. The contact pressure between the cell and substrate at equilibrium is predicted to depend on the curvature of the contacting substrate, but to be independent of the impingement force. The approach to equilibrium was rapid, such that the time-averaged stress for a two-second impingement was within 20% of the equilibrium value. These results have implications for the role of mechanical force in the formation of adhesive contacts.

Neutrophil adhesive contact dependence on impingement force.

Neutrophil capture and recruitment from the circulation requires the formation of specific receptor/ligand bonds under hydrodynamic forces. In the present study we examine bond formation between beta2-integrins on neutrophils and immobilized ICAM-1 while using micropipettes to control the force of contact between the cell and substrate. Magnesium was used to induce the high affinity conformation of the integrins, and bond formation was assessed by measuring the probability of adhesion during repeated contacts. Increasing the impingement force caused an increase in the contact area and led to a proportional increase in adhesion probability (from approximately 20 to 50%) over the range of forces tested (50-350 pN). In addition, different-sized beads were used to change the force per unit area in the contact zone (contact stress). We conclude that for a given contact stress, the rate of bond formation increases linearly with contact area, but that increasing contact stress results in higher intrinsic rates of bond formation.

Integrin activation by divalent ions affects neutrophil homotypic adhesion.

Activation of beta 2 integrins on leukocytes, via receptor clustering or affinity changes, is a key step in the inflammatory response. To evaluate the importance of integrin affinity changes for the formation of adhesive contacts, divalent cations were used to modulate beta 2-integrin affinity without causing a general activation of neutrophils. Two neutrophils were brought into repeated contact with micropipettes and the probability of forming an adhesive contact was measured for neutrophils exposed to different cations. In the presence of magnesium and manganese, which induce a high affinity integrin conformation, the adhesion frequency was 12%-14%. In the presence of calcium (which stabilizes the low-affinity state) the frequency of adhesion was reduced (2.4 +/- 2.1%) and in the absence of divalent cations there were no adhesive contacts. The adhesive probability was not affected by addition of soluble VCAM-1, but was significantly reduced to 7 +/- 3% in the presence of magnesium plus a soluble form of ICAM-1. Addition of a blocking anti-beta 2-integrin Fab fragment also significantly reduced the probability of forming an adhesive contact to 4 +/- 2%. Thus increased beta 2-integrin affinity promotes homotypic neutrophil adhesion during cell collisions, but the adhesion strength is weak compared to forces observed in cell arrest and migration.

[Prevalence of cardiovascular risk factors in first year university students]. / Prevalencia de factores de riesgo cardiovascular en ingresantes universitarios.

The prevalence of cardiovascular risk factors and their relation to a self-reported family history of disease was examined in 3,357 first year university students of Mar del Plata University (Argentine). The prevalence of family disease was 27.5% for hypercholesterolemia, 42.1% for hypertension, 26.9% for diabetes mellitus, 27.2% for obesity and 42.1% for cardiovascular disease. The percentual of 80.7% of the population surveyed showed at least one of these diseases in their previous family history. The prevalence of hypertension (systolic blood pressure levels > or = 140 mmHg) or/and diastolic blood pressure levels > or = 90 mmHg) was 7.0%. Hypertension was related to Body Mass Index (BMI), male sex and age. The percentual of 14.4% presented hypercholesterolemia (> or = 210 mg/dl), which was associated with age, BMI and family history of obesity and hypercholesterolemia. Nine hundred and eleven subjects (27.1%) were smokers. Differences related to sex were not found. Smoking was positively related to age and the career they had chosen. The examination detected one hundred and twenty-three (3.7%) students with cardiac problems. This was associated with a family history of cardiovascular disease. Preventive measures were suggested.

Infección por Enfermedad de Chagas, sífilis, brucelosis y TBC en trabajadores rurales del Partido de General Pueyrredón / Chagasic infection and other epidemiological outlooks in rural settlers of the General Pueyrredon District

Objetivo : determinar la prevalencia de infección chagásica, para sífilis y brucelosis, prevalencia de cicatriz BCG y otras variables epidemiológicas en una población de trabajadores de las áreas rurales de Mar del Plata concurrentes al Laboratorio de INE "Dr. Juan H. Jara" en los meses febrero y marzo de 1993. Material y métodos : a cada participante se le realizó una encuesta epidemiológica y la extracción de una muestra de sangre. Se efectuó reacción de Hemoaglutinación Indirecta (H.A.I.) y test de Inmunofluorescencia para Chagas (T.I.F.); V.D.R.L. y Microhemoaglutinación para Sífilis y test de Huddleson para Brucelosis. Se aplicó intradermoreacción P.P.D. y efectuó su lectura a las 72 hs. Resultados : se encuestaron 342 personas con edades comprendidas entre 14 y 65 años, el 89,2 por ciento de sexo masculino y 10,8 por ciento de sexo femenino. El 32 por ciento provenían de Bolivia, 30 por ciento de Santiago del Estero y el resto de otras provincias y países limítrofes. El 54 por ciento no asistió o lo hizo incompletamente a la escuela primaria, mostrando las mujeres mayor deterioro de su escolaridad. El 61,7 por ciento de los encuestados tiene intenciones de radicarse en la Pcia. de Buenos Aires (de estos, la tercera parte declaró ya estar redicado). El 40,2 por ciento de la población estudiada presentó infección por Tripanosoma cruzi. Se observó incremento de riesgo con la edad, lugar de nacimiento y menor escolaridad (estratificada por edad). No se observó diferencia estadísticamente significativa entre sexos. La tasa de positividad general para sífilis fue de 2,4 por ciento . A pesar de observarse factores de riesgo para brucelosis, la tasa de prevalencia fue cero. Sobre 265 encuestados, el 69,4 por ciento presentó una o más cicatrices BCG y el 23 por ciento reacción a P.P.D. con un halo de 10 o más mm. No hubo asociación entre presencia de cicatriz BCG y respuesta P.P.D. Conclusión : la alta prevalencia de infección chagásica enfatiza la necesidad de mantener un férreo control sobre los bancos de sangre y disponer de servicios cardiológicos adecuados para responder a esta problemática. Sería importante además, realizar vigilancia epidemiológica para sífilis y otras enfermedades de transmisión sexual

Infección por Enfermedad de Chagas, sífilis, brucelosis y TBC en trabajadores rurales del Partido de General Pueyrredón / Chagasic infection and other epidemiological outlooks in rural settlers of the General Pueyrredon District

Objetivo : determinar la prevalencia de infección chagásica, para sífilis y brucelosis, prevalencia de cicatriz BCG y otras variables epidemiológicas en una población de trabajadores de las áreas rurales de Mar del Plata concurrentes al Laboratorio de INE "Dr. Juan H. Jara" en los meses febrero y marzo de 1993. Material y métodos : a cada participante se le realizó una encuesta epidemiológica y la extracción de una muestra de sangre. Se efectuó reacción de Hemoaglutinación Indirecta (H.A.I.) y test de Inmunofluorescencia para Chagas (T.I.F.); V.D.R.L. y Microhemoaglutinación para Sífilis y test de Huddleson para Brucelosis. Se aplicó intradermoreacción P.P.D. y efectuó su lectura a las 72 hs. Resultados : se encuestaron 342 personas con edades comprendidas entre 14 y 65 años, el 89,2 por ciento de sexo masculino y 10,8 por ciento de sexo femenino. El 32 por ciento provenían de Bolivia, 30 por ciento de Santiago del Estero y el resto de otras provincias y países limítrofes. El 54 por ciento no asistió o lo hizo incompletamente a la escuela primaria, mostrando las mujeres mayor deterioro de su escolaridad. El 61,7 por ciento de los encuestados tiene intenciones de radicarse en la Pcia. de Buenos Aires (de estos, la tercera parte declaró ya estar redicado). El 40,2 por ciento de la población estudiada presentó infección por Tripanosoma cruzi. Se observó incremento de riesgo con la edad, lugar de nacimiento y menor escolaridad (estratificada por edad). No se observó diferencia estadísticamente significativa entre sexos. La tasa de positividad general para sífilis fue de 2,4 por ciento . A pesar de observarse factores de riesgo para brucelosis, la tasa de prevalencia fue cero. Sobre 265 encuestados, el 69,4 por ciento presentó una o más cicatrices BCG y el 23 por ciento reacción a P.P.D. con un halo de 10 o más mm. No hubo asociación entre presencia de cicatriz BCG y respuesta P.P.D. Conclusión : la alta prevalencia de infección chagásica enfatiza la necesidad de mantener un férreo control sobre los bancos de sangre y disponer de servicios cardiológicos adecuados para responder a esta problemática. Sería importante además, realizar vigilancia epidemiológica para sífilis y otras enfermedades de transmisión sexual

Inspiratory inhibition and rebound activation elicited by intermittent electrical bulbar stimulation in various states of pulmonary afferent vagal excitation.

In anesthetized rabbits spirogram and diaphragmatic activity were examined during electrical stimulation of regions of the medulla oblongata. The volleys were triggered by the animal's own respiration. 1. One volley of 120 msec duration at 100 pulses p.s., applied during inspiratory, caused an immediate and transient inhibition of the diaphragmatic activity. After the end of the volley and inspiratory rebound appeared: the tidal volume was increased and the inspiration was prolonged by some 150 msec. The respiratory rate decreased. 2. Continuous low or high frequency electrical stimulation of pulmonary stretch afferents caused an inspiratory or an expiratory effect respectively. In both conditions the effects of additional intermittent bulbar stimulation remained essentially unaltered. 3. By means of specially designed spirometer both pulmonary collapse and marked lung distension were produced. At low lung volume collapse afferents were excited. Inspiratory inhibition and rebound activation upon central stimulation persisted throughout the whole range of lung volume investigated; the rebound increase in tidal volume consecutive to the stimulus volley, however, was minimal in extreme lung distension. 4. Results suggest that the stimulation effects were the consequence of manipulation on intrinsic mechansims of the bulbar respiratory centre.