Monitoring and Intervention Strategies for Bluetongue Virus Epidemics in Rural India

点击翻译按钮获取中文摘要

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.