Modelling Neglected Tropical Diseases diagnostics: the sensitivity of skin snips for Onchocerca volvulus in near elimination and surveillance settings.

BACKGROUND: The African Programme for Onchocerciasis Control has proposed provisional thresholds for the prevalence of microfilariae in humans and of L3 larvae in blackflies, below which mass drug administration (MDA) with ivermectin can be stopped and surveillance started. Skin snips are currently the gold standard test for detecting patent Onchocerca volvulus infection, and the World Health Organization recommends their use to monitor progress of treatment programmes (but not to verify elimination). However, if they are used (in transition and in parallel to Ov-16 serology), sampling protocols should be designed to demonstrate that programmatic goals have been reached. The sensitivity of skin snips is key to the design of such protocols. METHODS: We develop a mathematical model for the number of microfilariae in a skin snip and parameterise it using data from Guatemala, Venezuela, Ghana and Cameroon collected before the start of ivermectin treatment programmes. We use the model to estimate sensitivity as a function of time since last treatment, number of snips taken, microfilarial aggregation and female worm fertility after exposure to 10 annual rounds of ivermectin treatment. RESULTS: The sensitivity of the skin snip method increases with time after treatment, with most of the increase occurring between 0 and 5 years. One year after the last treatment, the sensitivity of two skin snips taken from an individual infected with a single fertile female worm is 31 % if there is no permanent effect of multiple ivermectin treatments on fertility; 18 % if there is a 7 % reduction per treatment, and 0.6 % if there is a 35 % reduction. At 5 years, the corresponding sensitivities are 76 %, 62 % and 4.7 %. The sensitivity improves significantly if 4 skin snips are taken: in the absence of a permanent effect of ivermectin, the sensitivity of 4 skin snips is 53 % 1 year and 94 % 5 years after the last treatment. CONCLUSIONS: Our model supports the timelines proposed by APOC for post-MDA follow-up and surveillance surveys every 3-5 years. Two skin snips from the iliac region have reasonable sensitivity to detect residual infection, but the sensitivity can be significantly improved by taking 4 snips. The costs and benefits of using four versus two snips should be evaluated

Natural infection of Plasmodium brasilianum in humans: Man and monkey share quartan malaria parasites in the Venezuelan Amazon

AbstractBackgroundThe quartan malaria parasite Plasmodium malariae is the widest spread and best adapted human malaria parasite. The simian Plasmodium brasilianum causes quartan fever in New World monkeys and resembles P. malariae morphologically. Since the genetics of the two parasites are nearly identical, differing only in a range of mutations expected within a species, it has long been speculated that the two are the same. However, no naturally acquired infection with parasites termed as P. brasilianum has been found in humans until now.MethodsWe investigated malaria cases from remote Yanomami indigenous communities of the Venezuelan Amazon and analyzed the genes coding for the circumsporozoite protein (CSP) and the small subunit of ribosomes (18S) by species-specific PCR and capillary based-DNA sequencing.FindingsBased on 18S rRNA gene sequencing, we identified 12 patients harboring malaria parasites which were 100% identical with P. brasilianum isolated from the monkey, Alouatta seniculus. Translated amino acid sequences of the CS protein gene showed identical immunodominant repeat units between quartan malaria parasites isolated from both humans and monkeys.InterpretationThis study reports, for the first time, naturally acquired infections in humans with parasites termed as P. brasilianum. We conclude that quartan malaria parasites are easily exchanged between humans and monkeys in Latin America. We hypothesize a lack of host specificity in mammalian hosts and consider quartan malaria to be a true anthropozoonosis. Since the name P. brasilianum suggests a malaria species distinct from P. malariae, we propose that P. brasilianum should have a nomenclatorial revision in case further research confirms our findings. The expansive reservoir of mammalian hosts discriminates quartan malaria from other Plasmodium spp. and requires particular research efforts

Response to the Letter to the Editor by Eberhard et al.

In a Letter to the Editor, Eberhard et al. question the validity of our model of skin snip sensitivity and argue against the use of skin snips to evaluate onchocerciasis elimination by mass drug administration. Here we discuss their arguments and compare model predictions with observed data to assess the validity of our model

A rapid malaria appraisal in the Venezuelan Amazon

This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

Naturally acquired immune responses to malaria vaccine candidate antigens MSP3 and GLURP in Guahibo and Piaroa indigenous communities of the Venezuelan Amazon

BACKGROUND: Malaria transmission in most of Latin America can be considered as controlled. In such a scenario, parameters of baseline immunity to malaria antigens are of specific interest with respect to future malaria eradication efforts. METHODS: A cross-sectional study was carried out in two indigenous population groups in Amazonas/Venezuela. Data from the regional malaria documentation system were extracted and participants from the ethnic groups of the Guahibo (n = 180) and Piaroa (n = 295) were investigated for the presence of Plasmodium parasites and naturally acquired antibodies to Plasmodium falciparum antigens in serum. The GMZ2 vaccine candidate proteins MSP3 and GLURP were chosen as serological markers. RESULTS: The incidence of P. falciparum in both communities was found to be less than 2%, and none of the participants harboured P. falciparum at the time of the cross-sectional. Nearly a quarter of the participants (111/475; 23,4%) had positive antibody titres to at least one of the antigens. 53/475 participants (11.2%) were positive for MSP3, and 93/475 participants (19.6%) were positive for GLURP. High positive responses were detected in 36/475 participants (7.6%) and 61/475 participants (12.8%) for MSP3 and GLURP, respectively. Guahibo participants had significantly higher antibody titres than Piaroa participants. CONCLUSIONS: Considering the low incidence of P. falciparum, submicroscopical infections may explain the comparatively high anti-P. falciparum antibody concentrations

Procesamiento de señales EEG de un niño con TEA al desarrollar actividades de lectoescritura: determinación de potencia y cronología de eventos

Se presenta el análisis y procesamiento de señales electroencefalográficas (EEG) de un niño de 10 años con Trastorno del Espectro Autista al desarrollar actividades de lectoescritura, en este caso, relacionar en pruebas sucesivas palabras con su imagen representativa, como la palabra manzana con una imagen de una manzana. Una vez adquiridas las muestras, se lleva a cabo un análisis de potencia para cada canal mediante el Teorema de Wiener – Khinchine y posteriormente, mediante la Transformada Wavelet se determinan los momentos en los que hubo mayor actividad en cada electrodo. Con esta información se presenta la cronología de eventos de activación registrada por cada electrodo

Las huellas del río : narrativas de la violencia en Viento Seco y si el río hablara

El objetivo principal de esta investigación fue analizar las representaciones del conflicto colombiano narradas en las obras: Si el río hablara del teatro La Candelaria (2013) y Viento Seco (1953) de Daniel Caicedo, para a partir de su análisis comparativo, resaltar al río como un actor social y un elemento vivo que entreteje las historias, teniendo en cuenta los recursos y estilos literarios, narrativos, dramatúrgicos, escénicos, performativos e interdisplinares. Para tal fin, se seleccionaron las obras mencionadas anteriormente, a su vez se contrastaron las épocas de publicación de las mismas. Esto con la intención de obtener un análisis contextual completo.The main objective of this investigation was to analyze the Colombian conflicts representations narrated in the works: Si el río hablara of Teatro La Candelaria (2013) and Viento Seco (1953) by Daniel Caicedo to setting up a comparative analysis and highlight the river as a social actor and an alive element that interweaves the stories, taking account of the resources and literary styles, narratives, dramaturgical, scenic, performatives and interdisciplinary. For that purpose, the mentioned works were selected contrasting publication periods for themselves. All of this with the intention to obtain a complete contextual analysis

Evaluación de las técnicas de Doble Difusión, Ensayo Inmunoenzimático e Inmunoblotting en el diagnóstico de la hidatidosis humana en áreas tropicales

Hydatid disease in tropical areas poses a serious diagnostic problem due to the high frequence of cross-reactivity with other endemic helminthic infections. The enzyme-linked-immunosorbent assay (ELISA) and the double diffusion arc 5 showed respectively a sensitivity of 73% and 57% and a specificity of 84-95% and 100%. However, the specificity of ELISA was greatly increased by using ovine serum and phosphorylcholine in the diluent buffer. The hydatic antigen obtained from ovine cyst fluid showed three main protein bands of 64,58 and 30 KDa using SDS PAGE and immunoblotting. Sera from patients with onchocerciasis, cysticercosis, toxocariasis and Strongyloides infection cross-reacted with the 64 and 58 KDa bands by immunoblotting. However, none of the analyzed sera recognized the 30 KDa band, that seems to be specific in this assay. The immunoblotting showed a sensitivity of 80% and a specificity of 100% when used to recognize the 30 KDa band.La Hidatidosis en áreas tropicales representa un serio problema diagnóstico por la alta frecuencia de reactividad cruzada con otras infecciones helmínticas. Las técnicas de inmunoensayo enzimático (ELISA) y doble difusión arco 5 (DD5) mostraron una sensibilidad de 73 y 57 % y una especificidad de 84-95% y 100%, respectivamente. La especificidad en la técnica de ELISA, fue mejorada sustancialmente al emplear como diluyente de los sueros una solución buffer conteniendo suero ovino normal y fosforilcolina. En líquido obtenido de hidátides de Echinococcus granulosus de origen ovino, se demostraron tres bandas de origen proteico de 64, 58 y 30 KDa de peso molecular, empleando SDS e inmunoblotting. Sueros de pacientes con estrongiloidiasis, oncocer-cosis, toxocariasis y cisticercosis reaccionaron con las bandas de 64 y 58 KDa en inmunoblotting. Sin embargo ninguno de los sueros reconoció la banda de 30 KD, la cual parece ser específica para este ensayo. La técnica de inmunobloting empleada para poner en evidencia la banda de 30 KDa con fines diagnósticos, exhibió una sensibilidad de 80% y una especificidad de 100%