Monitoring and Intervention Strategies for Bluetongue Virus Epidemics in Rural India

蓝舌病病毒（BTV）是一种由库蠓叮咬蠓传播的反刍动物虫媒病毒病原体，可引起绵羊（特别是某些细羊毛和羊肉品种）蓝舌病。在20世纪80年代，临床BT开始出现在印度本土绵羊品种的羊群中，特别是在南部各州，这可能是通过绵羊育种计划引入的外来病毒株的结果。流行病学的这一变化导致了这些地区以家庭为基础的自给农业社区的暴发，此后，BTV已成为当地畜群饲养和生产力的重大制约因素。此外，在雨养农业地区，定期发生大规模疾病暴发，据认为这与季风条件的时间和强度对传播BTV的病媒种群的影响有关。由于印度南部有21种血清型的BTV流行，而且绝大多数人口接种疫苗的费用过高，媒介控制仍然是在现场防治BTV传播的唯一可行方法。尽管如此，实际上没有关于这一作用中现有技术效率的定量数据来为控制战略提供信息。我们将采用一种涉及数学建模、昆虫学和化学生态学的多学科方法，研究印度南部各邦BTV的流行病学，并制定预测、监测和缓解技术，以减少BT在该地区的影响。首先，我们将使用根据气候和土地利用模式划定土地区域的制图技术来描述印度南部的特征。然后，我们将在整个地区建立代表这些因素和所采用的畜牧业类型的实地站点（重点是小块土地和无地畜牧业工人）。在确定了这些地点的特征后，我们将使用诱光法确定成虫的季节性和分布，并通过直接从牲畜身上收集库蠓进行实地调查。这些研究将与收集到的蠓个体中BTV的检测相结合，首次确定在印度南部参与传播的物种的区域差异。然后还将通过实地调查确定已确定的主要病媒物种的幼虫发育地点。利用成虫季节性、幼虫栖息地偏好和印度南部BT病例的历史调查数据，我们将对季风条件与成虫/BT活动之间的关系进行建模，以评估基于气象变量建立主要BTV流行预警系统的潜力。提供基本的流行病学知识还将有助于评估基于养殖场的库蠓控制技术，这些技术可用于以成本中立的方式减少自给农民的BTV传播。我们将在实验室和实地考察传统的和新的控制手段。前者将包括使用幼虫场地改造，或使用村民可获得的传统的、对环境影响小的杀虫产品进行有针对性的治疗，此外还将使用猪舍。此外，通过已确定的库蠓病媒获得的宿主位置信息将有助于采用基于掩蔽性化学物质应用的新型干预策略，这也可以在中期减少这些种群对合成杀虫剂的使用。将通过监测牲畜中的病毒感染来检查这些技术组合的效果，作为实地影响证据的金标准。然后将对这些数据进行评估，以便将其纳入用户群体的日常生活，作为提高反刍动物生产力和控制人类和兽医病原体媒介的更广泛传播框架的一部分。

Bluetongue virus (BTV) is an arboviral pathogen of ruminants spread by Culicoides biting midges, which causes the disease bluetongue (BT) in sheep (particularly certain fine wool and mutton breeds). During the 1980's clinical BT began to appear in flocks of native Indian breeds of sheep, particularly in the southern states, possibly as a result of exotic strains of the virus introduced via sheep-breeding programmes. This change in epidemiology led to outbreaks among family-based subsistence farming communities in these areas, and BTV has since been become a significant constraint in both the rearing and productivity of indigenous flocks. In addition, in rain-fed agricultural areas, massive periodic outbreaks of disease occur that are thought to be related to the influence of timing and intensity of monsoon conditions on populations of vectors responsible for spreading BTV. Due to the circulation of 21 serotypes of BTV in southern India and the prohibitive costs of vaccination to the vast majority of the population, vector control remains the only feasible way of combating BTV transmission in the field. Despite this, virtually no quantitative data concerning the efficiency of available techniques in this role is available to inform control strategies. We will adopt a multidisciplinary approach involving mathematical modelling, entomology and chemical ecology to examine the epidemiology of BTV in the southern Indian states and to produce prediction, monitoring and mitigation techniques that can reduce the impact of BT in this region. Initially we will characterise southern India using mapping techniques that delineate land areas according to climate and land use patterns. We will then establish field sites across the region that are representative of both these factors and also the types of husbandry employed (with an emphasis on small holdings and landless husbandry workers). Having characterised these sites, we will then use light trapping to define adult seasonality and distribution and ground truth this survey with direct collection of Culicoides from livestock. These studies will be combined with detection of BTV within collected individual midges to define regional variation in which species are involved in transmission in southern India for the first time. The larval development sites of major vector species identified will then also be characterised via field investigations. Using data generated on adult seasonality, larval habitat preference and historic surveys of BT cases across southern India, we will then model the relationship between monsoon conditions and adult Culicoides/BT activity to assess the potential to produce an early warning system for major BTV epidemics based on meteorological variables. The provision of fundamental epidemiological knowledge will also enable an assessment of husbandry-based control techniques for Culicoides that could be employed to reduce BTV transmission by subsistence farmers in a cost-neutral fashion. We will examine traditional and novel means of control, both in the laboratory and in the field. The former will include the use of larval site modification, or targeted treatment with traditional, low environmental impact, insecticidal products available to villagers and additionally the use of stabling. In addition, information regarding host location by identified vector Culicoides will allow novel intervention strategies based upon the application of masking semiochemicals that could also reduce the use of synthetic insecticides by these communities in the medium term. The effect of combinations of these techniques will be examined via monitoring viral infection in livestock, as a gold standard for evidence of impact in the field. These data will then be assessed for integration into the everyday lives of user groups as part of wider dissemination frameworks for improvement of ruminant productivity and control of vectors of human and veterinary pathogens.