McDermott Emily G, Mayo Christie E, Gerry Alec C, Laudier Damien, MacLachlan N James, Mullens Bradley A
Department of Entomology, University of California, Riverside, CA, 92521, USA.
Department of Microbiology, Immunology & Pathology, Colorado State University, Fort Collins, CO, 80523, USA.
Parasit Vectors. 2015 Sep 17;8:460. doi: 10.1186/s13071-015-1062-4.
Pathogen manipulation of host behavior can greatly impact vector-borne disease transmission, but almost no attention has been paid to how it affects disease surveillance. Bluetongue virus (BTV), transmitted by Culicoides biting midges, is a serious disease of ruminant livestock that can cause high morbidity and mortality and significant economic losses. Worldwide, the majority of surveillance for Culicoides to assess BTV transmission risk is done using UV-light traps. Here we show that field infection rates of BTV are significantly lower in midge vectors collected using traps baited with UV light versus a host cue (CO2).
We collected Culicoides sonorensis midges in suction traps baited with CO2, UV-light, or CO2 + UV on three dairies in southern California to assess differences in the resulting estimated infection rates from these collections. Pools of midges were tested for BTV by qRT-PCR, and maximum likelihood estimates of infection rate were calculated by trap. Infection rate estimates were also calculated by trapping site within a dairy. Colonized C. sonorensis were orally infected with BTV, and infection of the structures of the compound eye was examined using structured illumination microscopy.
UV traps failed entirely to detect virus both early and late in the transmission season, and underestimated virus prevalence by as much as 8.5-fold. CO2 + UV traps also had significantly lower infection rates than CO2-only traps, suggesting that light may repel infected vectors. We found very high virus levels in the eyes of infected midges, possibly causing altered vision or light perception. Collecting location also greatly impacts our perception of virus activity.
Because the majority of global vector surveillance for bluetongue uses only light-trapping, transmission risk estimates based on these collections are likely severely understated. Where national surveillance programs exist, alternatives to light-trapping should be considered. More broadly, disseminated infections of many arboviruses include infections in vectors' eyes and nervous tissues, and this may be causing unanticipated behavioral effects. Field demonstrations of pathogen-induced changes in vector behavior are quite rare, but should be studied in more systems to accurately predict vector-borne disease transmission.
病原体对宿主行为的操控会极大地影响媒介传播疾病的传播，但几乎无人关注其对疾病监测的影响。由库蠓叮咬传播的蓝舌病毒（BTV）是反刍家畜的一种严重疾病，可导致高发病率和死亡率以及重大经济损失。在全球范围内，大多数用于评估BTV传播风险的库蠓监测是使用紫外线诱捕器进行的。在此我们表明，与使用宿主线索（二氧化碳）诱饵诱捕的蠓相比，使用紫外线诱饵诱捕的蠓中BTV的野外感染率显著更低。
我们在加利福尼亚州南部的三个奶牛场，用二氧化碳、紫外线或二氧化碳 + 紫外线诱饵的吸气式诱捕器收集索诺拉库蠓，以评估这些收集结果中估计感染率的差异。通过qRT-PCR检测蠓群中的BTV，并按诱捕器计算感染率的最大似然估计值。还按奶牛场内的诱捕地点计算感染率估计值。用BTV对定殖的索诺拉库蠓进行口服感染，并使用结构照明显微镜检查复眼结构的感染情况。
紫外线诱捕器在传播季节早期和晚期都完全未能检测到病毒，并且将病毒流行率低估了多达8.5倍。二氧化碳 + 紫外线诱捕器的感染率也显著低于仅使用二氧化碳的诱捕器，这表明光线可能会驱赶受感染的媒介。我们在受感染蠓的眼睛中发现了非常高的病毒水平，这可能会导致视力或光感知改变。收集地点也极大地影响我们对病毒活动的认知。
由于全球大多数针对蓝舌病的媒介监测仅使用灯光诱捕，基于这些收集结果的传播风险估计可能被严重低估。在有国家监测计划的地方，应考虑采用灯光诱捕的替代方法。更广泛地说，许多虫媒病毒的传播性感染包括在媒介眼睛和神经组织中的感染，这可能会导致意想不到的行为影响。病原体诱导媒介行为变化的实地演示相当罕见，但应在更多系统中进行研究，以准确预测媒介传播疾病的传播。
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