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Rift Valley fever (RVF) is endemic in northern Senegal, a Sahelian area characterized by a temporary pond network that drive both RVF mosquito population dynamics and nomadic herd movements. To investigate the mechanisms that explain RVF recurrent circulation, we modelled a realistic epidemiological system at the pond level integrating vector population dynamics, resident and nomadic ruminant herd population dynamics, and nomadic herd movements recorded in Younoufere area. To calibrate the model, serological surveys were performed in 2015–2016 on both resident and nomadic domestic herds in the same area. Mosquito population dynamics were obtained from a published model trained in the same region. Model comparison techniques were used to compare five different scenarios of virus introduction by nomadic herds associated or not with vertical transmission in Aedes vexans. Our serological results confirmed a long lasting RVF endemicity in resident herds (IgG seroprevalence rate of 15.3%, n = 222), and provided the first estimation of RVF IgG seroprevalence in nomadic herds in West Africa (12.4%, n = 660). Multivariate analysis of serological data suggested an amplification of the transmission cycle during the rainy season with a peak of circulation at the end of that season. The best scenario of virus introduction combined yearly introductions of RVFV from 2008 to 2015 (the study period) by nomadic herds, with a proportion of viraemic individuals predicted to be larger in animals arriving during the 2nd half of the rainy season (3.4%). This result is coherent with the IgM prevalence rate (4%) found in nomadic herds sampled during the 2nd half of the rainy season. Although the existence of a vertical transmission mechanism in Aedes cannot be ruled out, our model demonstrates that nomadic movements are sufficient to account for this endemic circulation in northern Senegal., Author summary Rift Valley fever (RVF) is one of the most important vector borne disease in Africa, seriously affecting the health of domestic ruminants and humans and leading to severe economic consequences. This disease is endemic in northern Senegal, a Sahelian area characterized by a temporary pond network that drive both RVF mosquito population dynamics and nomadic herd movements. Two non-exclusive mechanisms may support this endemicity: recurrent introductions of the virus by nomadic animals, and vertical transmission of the virus (i.e. from infected female mosquito to eggs) in local Aedes populations. The authors followed resident and nomadic domestic herds for 1 year. They used the data thus obtained to model a realistic epidemiological system at the pond level integrating vector population dynamics, resident and nomadic ruminant herd population dynamics. They found that the best scenario explaining RVF remanence combined yearly introductions of RVFV by nomadic herds, with a viraemic proportion predicted to be larger in animals arriving during the 2nd half of the rainy season, which is consistent with an amplification of virus circulation in the area during the rainy season. Although the existence of a vertical transmission mechanism in Aedes cannot be ruled out, their results demonstrates that nomadic movements are sufficient to account for this endemic circulation in northern Senegal.

Au Sénégal, l’adhésion des éleveurs aux tests tuberculiniques est confrontée à la durée de leur réalisation au premier passage dans le troupeau. L’objectif de cette étude est d’évaluer si le fait de substituer la mesure non effectuée au Jour 0 (J0) une mesure en un point symétrique sur la face opposée de l’encolure au Jour 3 (J3) est envisageable. Ainsi, en octobre 2016, l’essai a été mené sur dix zébus Gobras de race pure (d’âge et de sexe différents) du Centre de Recherches Zoonotiques de Dahra Djoloff (Louga). Les mesures ont été prises et répétées dix fois sur le même animal, avec le même cutimètre, le même jour, par chacun des trois opérateurs. L’épaisseur moyenne du pli cutané était de 9,14 mm [2,09-25,62 mm (IC 95%)] et 9,7 mm [3,67- 15,92 mm (IC 95%)] pour les faces droites et gauche respectivement. Suivant la méthode de Charrette et le procédé VARCOMP du logiciel SAS, la précision et la fiabilité étaient plus élevées pour la face gauche (reproductibilité de 90,14% et répétabilité de 86,66%) que la face droite (reproductibilité de 86,86% et répétabilité de 82,46%). Il a été montré dans cette étude qu’il est possible de remplacer la mesure de l’épaisseur cutanée à J0 par une autre effectuée au point symétrique du lieu de la tuberculination à J3, chez le bovin Gobra.© 2019 International Formulae Group. All rights reservedMots clés: Zébu-Gobra, Mesure Plis de peau, Reproductibilité-Répétabilité, Tuberculination, SénégalEnglish Title: Reliability and Accuracy of skin fold measurement in two symmetrical points of the neck during in zebu Gobra, Bos indicus Linnaeus, 1758 in SenegalEnglish AbstractIn Senegal, the participation of breeders to tuberculin test is hampered by the duration of the first passage in the herd. The objective of this study is to evaluate whether the substitution of the measurement not performed on Day 0 (D0) by a measurement at a symmetrical point on the opposite side of the neck on Day 3 (D3) is possible. Thus, in October 2016, a trial was carried out on ten zebu Gobra of pure breed (of different sex and age) of the Centre de Recherches Zoonotiques de Dahra Djoloff (Louga, Senegal). Measures were taken and repeated ten times on the same animal, with the same calliper, the same day, by each of three operators. The average thickness of skinfold is 9.14 mm [2.09-25.62 mm (IC 95%)] and 9.7 mm [3.67-15.92 mm (IC 95%)] for right and left sides respectively. According to the method of Charrette and VARCOMP procedure under SAS software, the accuracy and reliability are higher for left side (reproducibility of 90.14% and repeatability of 86.66%) than right side (reproducibility of 86.86% and repeatability of 82.46%). This study shows that it is possible to replace the measure of skin thickness at D0 by another one at a symmetrical point of tuberculin inoculation point at D3 for Gobra cattle.© 2019 International Formulae Group. All rights reservedKeywords: Zebu Gobra; Measure; Skinfold; Repeatability-Reproducibility, Senegal