Olive Marie-Marie, Chevalier Véronique, Grosbois Vladimir, Tran Annelise, Andriamandimby Soa-Fy, Durand Benoit, Ravalohery Jean-Pierre, Andriamamonjy Seta, Rakotomanana Fanjasoa, Rogier Christophe, Heraud Jean-Michel
CIRAD, Animal and Integrated Risk Management (AGIRs) Unit, Montpellier, France.
Institut Pasteur de Madagascar, Virology Unit, Antananarivo, Madagascar.
PLoS Negl Trop Dis. 2016 Jul 14;10(7):e0004827. doi: 10.1371/journal.pntd.0004827. eCollection 2016 Jul.
Rift Valley fever (RVF) is a vector-borne disease affecting ruminants and humans. Madagascar was heavily affected by RVF in 2008-2009, with evidence of a large and heterogeneous spread of the disease. The identification of at-risk environments is essential to optimize the available resources by targeting RVF surveillance in Madagascar. Herein, the objectives of our study were: (i) to identify the environmental factors and areas favorable to RVF transmission to both cattle and human and (ii) to identify human behaviors favoring human infections in Malagasy contexts.
METHODOLOGY/PRINCIPAL FINDINGS: First, we characterized the environments of Malagasy communes using a Multiple Factor Analysis (MFA). Then, we analyzed cattle and human serological data collected at national level using Generalized Linear Mixed Models, with the individual serological status (cattle or human) as the response, and MFA factors, as well as other potential risk factors (cattle density, human behavior) as explanatory variables. Cattle and human seroprevalence rates were positively associated to humid environments (p<0.001). Areas with high cattle density were at risk (p<0.01; OR = 2.6). Furthermore, our analysis showed that frequent contact with raw milk contributed to explain human infection (OR = 1.6). Finally, our study highlighted the eastern-coast, western and north-western parts as high-risk areas for RVF transmission in cattle.
CONCLUSIONS/SIGNIFICANCE: Our integrated approach analyzing environmental, cattle and human datasets allow us to bring new insight on RVF transmission patterns in Madagascar. The association between cattle seroprevalence, humid environments and high cattle density suggests that concomitant vectorial and direct transmissions are critical to maintain RVF enzootic transmission. Additionally, in the at-risk humid environment of the western, north-western and the eastern-coast areas, suitable to Culex and Anopheles mosquitoes, vectorial transmission probably occurs in both cattle and human. The relative contribution of vectorial or direct transmissions could be further assessed by mathematic modelling.
裂谷热（RVF）是一种由媒介传播的疾病，可影响反刍动物和人类。马达加斯加在2008 - 2009年受到裂谷热的严重影响，有证据表明该疾病出现了大规模且分布不均的传播。识别高危环境对于通过在马达加斯加针对性地开展裂谷热监测来优化可用资源至关重要。在此，我们研究的目标是：（i）识别有利于向牛和人类传播裂谷热的环境因素和区域，以及（ii）识别在马达加斯加背景下有利于人类感染的人类行为。
方法/主要发现：首先，我们使用多因素分析（MFA）对马达加斯加各公社的环境进行了特征描述。然后，我们使用广义线性混合模型分析了在国家层面收集的牛和人类血清学数据，将个体血清学状态（牛或人类）作为响应变量，将多因素分析因素以及其他潜在风险因素（牛密度、人类行为）作为解释变量。牛和人类的血清阳性率与潮湿环境呈正相关（p<0.001）。牛密度高的地区存在风险（p<0.01；比值比 = 2.6）。此外，我们的分析表明，频繁接触生牛奶有助于解释人类感染情况（比值比 = 1.6）。最后，我们的研究突出了东海岸、西部和西北部地区是牛群中裂谷热传播的高危地区。
结论/意义：我们综合分析环境、牛和人类数据集的方法使我们能够对马达加斯加裂谷热的传播模式有新的认识。牛血清阳性率、潮湿环境和高牛密度之间的关联表明，媒介传播和直接传播同时存在对于维持裂谷热的动物间传播至关重要。此外，在西部、西北部和东海岸地区的高危潮湿环境中，适合库蚊和按蚊生存，媒介传播可能在牛和人类中都发生。媒介传播或直接传播的相对贡献可通过数学建模进一步评估。
