361 research outputs found
Leishmaniose en Equateur : 5. Leishmaniose et anthropisation sur la façade pacifique
On a Ă©tudiĂ© l'impact de l'anthropisation du milieu forestier sur l'incidence de la leishmaniose, due Ă #Leishmania panamensis, dans trois stations cĂŽtiĂšres de l'Equateur, Corriente Grande, en forĂȘt primaire, Paraiso Escondido et La Tablada, en forĂȘt secondarisĂ©e; on a considĂ©rĂ© aussi la situation des maisons isolĂ©es en milieu dĂ©forestĂ© dans les deux derniĂšres stations. En parallĂšle, on a Ă©tudiĂ© la densitĂ© des espĂšces de phlĂ©botomes anthropophiles, particuliĂšrement #Lutzomyia trapidoi, dans le milieu domestique et les cafĂ©iĂšres adjacentes, ainsi qu'en sous-bois. L'incidence de la leishmaniose Ă©tait quasiment nulle en forĂȘt primaire, alors qu'elle oscillait entre 106 et 147 °/oo en forĂȘt plus ou moins dĂ©gradĂ©e. A Corriente Grande, aucun #Lu. trapidoi reprĂ©sentait plus de 83 % des captures en sous-bois et dans les cafĂ©iĂšres (41 Homme/heure), ainsi que dans les maisons (10,6 H/h). A La Tablada, en milieu domestique, #Lu. gomezi Ă©tait l'espĂšce dominante : 2,8 H/h contre 1 H/h #Lu. trapidoi, dans les cafĂ©iĂšres et en sous-bois #Lu. trapidoi Ă©tait l'espĂšce dominante, 21 H/h et 14 H/h. En forĂȘt primaire trĂšs humide, la transmission peut ĂȘtre trĂšs faible. En milieu secondarisĂ©, les cafĂ©iĂšres proches des habitations procurent un excellent biotope aux populations de #Lu. trapidoi; le cycle de #L. panamensis s'est adaptĂ© Ă cette situation Ă©cologique en se rapprochant des maisons, les rĂ©servoirs circulant dans les cafĂ©iĂšres. En milieu dĂ©forestĂ©, on ne constate plus de nuisances de phlĂ©botomes et plus de transmission de leishmaniose. (RĂ©sumĂ© d'auteur
Elimination of onchocerciasis in Ecuador: findings of post-treatment surveillance.
BACKGROUND: The Esmeraldas focus of onchocerciasis in Ecuador expanded geographically during the 1980s and was associated with severe ocular and skin disease. Mass drug administration (MDA) with ivermectin started in 1991, initially once but later twice a year, in the principle endemic focus followed by all satellite foci. Treatment was stopped in 2009 when entomological assessments determined that transmission of Onchocerca volvulus had been interrupted. METHODS: Three years after the cessation of ivermectin treatment in 2012, as defined by the WHO guidelines for onchocerciasis elimination, blackfly collections were done in four sentinel sites in former hyperendemic areas. The presence of infective larvae in local vectors, Simulium exiguum and Simulum quadrivittatum, was assessed by detection of O. volvulus DNA by PCR. Additional flies captured in four extra-sentinel sites located in former hyper- and mesoendemic dispersed isolated areas were also assessed. RESULTS: The results from 68,310 captured blackflies, 40,114 from four sentinel villages in the previously hyperendemic areas (Corriente Grande, El Tigre, San Miguel on RĂo Cayapas and Naranjal on RĂo CanandĂ©) and 28,197 from extra-sentinel locations, were all negative for the presence of O. volvulus. These extra-sentinel sites (HualpĂ on RĂo Hoja Blanca, CapulĂ on RĂo Onzole, La Ceiba on RĂo TululvĂ and MedianĂa on RĂo Verde) were included to provide additional evidence of the impact of MDA on the transmission of O. volvulus in isolated endemic areas. CONCLUSIONS: Our data indicate that transmission of O. volvulus has been stopped in all endemic areas in Ecuador, including all satellite foci outside the main focus. These findings indicate that a strategy of ivermectin distribution twice a year to over 85% of the treatment-eligible population was effective in eliminating the infection from Ecuador in a focus with a highly competent primary vector, S. exiguum, and where the infection rates were equal to or greater than observed in many onchocerciasis foci in Africa
Onchocerciasis in Ecuador: Prevalence of Infection on the Ecuador-Colombia Border in the Province of Esmeraldas
Leishmaniose en Equateur : 1. Incidence de la leishmaniose tégumentaire sur la façade pacifique
Une enquĂȘte porte Ă porte sur 961 personnes dans deux stations de la cĂŽte Pacifique de l'Equateur a permis d'Ă©valuer l'incidence et la prĂ©valence de la leishmaniose tĂ©gumentaire Ă #Leishmania panamensis$, et de noter ses manifestations cliniques. Dans les collines subandines, Ă Paraiso Escondido, la prĂ©valence de cas actifs Ă©tait de 4,8 %; dans les collines de la cordillĂšre littorale, elle Ă©tait de 3,6 %, et dans les deux cas il n'y avait pas de diffĂ©rence significative entre les sexes. L'incidence de nouveaux cas en 1991 Ă©tait forte, 147 °/oo Ă Paraiso Escondido, et 106 °/oo Ă La Tablada. La prĂ©valence cumulĂ©e atteignait 66 % Ă Paraiso Escondido, et 47 % Ă La Tablada. 62 % des patients des deux stations prĂ©sentaient une seule lĂ©sion ou cicatrice. Autochtones et migrants se contaminent dans leurs cinq premiĂšres annĂ©es d'existence en zone d'endĂ©mie. NĂ©ammoins, l'incidence reste Ă©levĂ©e dans toutes les classes d'Ăąge en raison du grand nombre de migrants (50 %). Les questionnaires ont rĂ©vĂ©lĂ© une contamination en saison sĂšche, de juillet jusqu'Ă la fin d'annĂ©e. La moustiquaire Ă©tait utilisĂ©e comme protection contre les phlĂ©botomes. Ces caractĂ©ristiques clinico-Ă©pidĂ©miologiques Ă©taient corroborĂ©es par celles, obtenues en dĂ©tection passive, Ă l'HĂŽpital A. Egas de Santo Domingo. La contamination de jeunes enfants et d'adultes des deux sexes, les lĂ©sions Ă la face, suggĂšrent une transmission domiciliaire. (RĂ©sumĂ© d'auteur
Leishmaniose en Equateur : 4. Infestation naturelle du chien par Leishmania panamensis
Dans deux stations de la plaine cÎtiÚre d'Equateur, région endémique de leishmaniose à #Leishmania panamensis, 34 chiens ont été contrÎlés aux plans clinique, sérologique et parasitologique; des tests d'immunofluorescence indirecte et d'électrosynérÚse, des ponctions ganglionnaires, des biopsies de lésions ont été pratiqués. De deux chiens présentant des lésions suspectes, un seul avait des lésions de la truffe et du scrotum infectées par des #Leishmania. La souche isolée a été rapportée à #L. panamensis (complexe #L. guyanensis). L'atteinte leishmanienne était strictement tégumentaire. Dans la zone d'étude, le chien semble un hÎte accidentel. (Résumé d'auteur
Leishmaniose en Equateur : 6. Note épidémiologique et entomologique sur le foyer de leishmaniose de Zumba
La rĂ©gion de Zumba se trouve au sud de la province mĂ©ridionale amazonienne d'Equateur de Zamora-Chinchipe, considĂ©rĂ©e comme la seconde zone d'endĂ©mie leishmanienne de ce pays. Une enquĂȘte clinico-Ă©pidĂ©miologique a Ă©tĂ© effectuĂ©e sur 83 patients en dĂ©tection passive. De plus, tous les biotopes du foyer de Zumba, dont les habitations, ont Ă©tĂ© Ă©chantillonĂ©s, de fĂ©vrier Ă septembre 92, pour la rĂ©colte des phlĂ©botomes au piĂšge lumineux et sur appĂąt humain (2.547 phlĂ©botomes rĂ©coltĂ©s). La faune anthrophile est pauvre et trois espĂšces seulement ont Ă©tĂ© observĂ©es. #Lutzomyia serrana est une espĂšce abondante piquant mĂȘme de jour. #Lu. maranonensis est une nouvelle espĂšce proche de #Lu. nevesi. Lu. castanea, autre nouvelle espĂšce, est rare. La localisation de nombreuses lĂ©sions Ă la face suggĂšre, au moins en partie, une transmission domiciliaire, pour laquelle #Lu. serrana serait un candidat-vecteur possible Ă©tant donnĂ© son omniprĂ©sence et son anthropophile. (RĂ©sumĂ© d'auteur
Enhancement of Stochastic Resonance in distributed systems due to a selective coupling
Recent massive numerical simulations have shown that the response of a
"stochastic resonator" is enhanced as a consequence of spatial coupling.
Similar results have been analytically obtained in a reaction-diffusion model,
using "nonequilibrium potential" techniques. We now consider a field-dependent
diffusivity and show that the "selectivity" of the coupling is more efficient
for achieving stochastic-resonance enhancement than its overall value in the
constant-diffusivity case.Comment: 10 pgs (RevTex), 4 figures, submitted to Phys.Rev.Let
Stochastic resonance between dissipative structures in a bistable noise-sustained dynamics
We study an extended system that without noise shows a monostable dynamics,
but when submitted to an adequate multiplicative noise, an effective bistable
dynamics arise. The stochastic resonance between the attractors of the
\textit{noise-sustained dynamics} is investigated theoretically in terms of a
two-state approximation. The knowledge of the exact nonequilibrium potential
allows us to obtain the output signal-to-noise ratio. Its maximum is predicted
in the symmetric case for which both attractors have the same nonequilibrium
potential value.Comment: RevTex, 13 pages, 6 figures, accepted in Physical Review
Learning to Learn: Theta Oscillations Predict New Learning, which Enhances Related Learning and Neurogenesis
Animals in the natural world continuously encounter learning experiences of varying degrees of novelty. New neurons in the hippocampus are especially responsive to learning associations between novel events and more cells survive if a novel and challenging task is learned. One might wonder whether new neurons would be rescued from death upon each new learning experience or whether there is an internal control system that limits the number of cells that are retained as a function of learning. In this experiment, it was hypothesized that learning a task that was similar in content to one already learned previously would not increase cell survival. We further hypothesized that in situations in which the cells are rescued hippocampal theta oscillations (3â12 Hz) would be involved and perhaps necessary for increasing cell survival. Both hypotheses were disproved. Adult male Sprague-Dawley rats were trained on two similar hippocampus-dependent tasks, trace and very-long delay eyeblink conditioning, while recording hippocampal local-field potentials. Cells that were generated after training on the first task were labeled with bromodeoxyuridine and quantified after training on both tasks had ceased. Spontaneous theta activity predicted performance on the first task and the conditioned stimulus induced a theta-band response early in learning the first task. As expected, performance on the first task correlated with performance on the second task. However, theta activity did not increase during training on the second task, even though more cells were present in animals that had learned. Therefore, as long as learning occurs, relatively small changes in the environment are sufficient to increase the number of surviving neurons in the adult hippocampus and they can do so in the absence of an increase in theta activity. In conclusion, these data argue against an upper limit on the number of neurons that can be rescued from death by learning
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