Near-Infrared Spectroscopy: A One-Stop-Shop for Mosquito Epidemiological Monitoring?

疟疾、登革热、基孔肯雅热和寨卡等蚊媒疾病在世界热带地区造成巨大痛苦。控制这些疾病的主要方法之一是使用杀虫剂杀死蚊子，防止它们在人与人之间传播感染。每年都有数百万英镑用于蚊虫控制，但令人惊讶的是，没有简单的方法来评估这些干预措施杀死蚊子或防止它们传播疾病的能力。由于当地的天气模式，一个地区叮咬蚊子的数量每天都有很大的波动，因此诱捕器中捕获的蚊子数量不能很好地预测种群的大小。更重要的是，蚊子的数量本身并不是一个很好的风险预测指标，因为许多疾病需要几天的时间才能在蚊子体内发展，并找到它们的传播途径。这意味着只有年龄较大的蚊子才能传播感染。因此，蚊子年龄对于评估灭蚊干预措施的有效性非常重要，但目前还没有简单、准确的方法来评估蚊子种群的年龄。近红外光谱（NIRS）是一种新的年龄分级和物种识别技术，已在实验室中开发。它通过测量一束光在蚊子变老时从蚊子身体上反射的不同来预测蚊子的年龄。与其他方法不同，NIRS不需要昂贵的化学品或程序，任何人只要经过最少的培训就可以进行。这使得它可以作为一种常规的方法来监测蚊子的年龄在外地使用。目前，NIRS不能非常准确地预测单个蚊子的年龄，并且只对实验室中饲养的蚊子进行了测试，这些蚊子可能比野外捕获的蚊子更均匀（因此给出更准确的结果）。然而，对于疾病控制来说，了解蚊子种群的平均年龄比个体的年龄更重要。我们的初步工作表明，如果我们改变分析NIRS输出的方式，我们可以对蚊子种群的平均年龄进行高度精确的预测。该项目打算将NIRS从实验室带到实地，并测试它是否足够好，能够用于蚊子种群的常规监测。该项目将使用半现场和现场数据来操作该技术，并概述需要捕获多少蚊子（以及需要多少天），以便作出足够准确的估计，以指导灭蚊工作的部署。这项工作将集中在两种最重要的蚊媒传染病：疟疾（2015年造成43.8万人死亡）和登革热（每年感染4亿人）。然而，这里开发的技术可以应用于其他疾病和蚊子物种。NIRS还可用于区分肉眼无法区分的密切相关的蚊子物种。这一点很重要，因为并非所有这些蚊子都具有相同的传播疾病能力，并且受到控制干预措施的影响也不同。与年龄分级类似，NIRS区分物种的能力需要在实地进行更严格的测试。还有证据表明，NIRS可能能够检测蚊子是否感染了导致登革热的病毒。这将首先在布基纳法索的实验室进行疟疾测试，然后在实地进行。目前，蚊子的种类、年龄和感染状况是使用各种费力和昂贵的程序来估计的，这些程序排除了在世界上较贫穷地区将其用作常规监测工具的可能性。一种同时进行所有三种测试的单一、廉价的方法将对公共卫生产生重大影响：我们可以更便宜、更快速地描述疾病传播的风险，评估控制计划的有效性。

Mosquito borne diseases such as malaria, dengue, chikungunya and zika cause huge suffering in tropical regions of the world. One of the main approaches to controlling these diseases is to use insecticides to kill mosquitoes and prevent them from transmitting the infection from person to person. Millions of pounds are spent on mosquito control each year though surprisingly there is no simple method for evaluating the ability of these interventions to kill mosquitoes or prevent them from transmitting disease. The number of biting mosquitoes in an area fluctuates substantially from day to day due to local weather patterns so the number of mosquitoes caught in traps is a poor predictor of the size of the population. More importantly the number of mosquitoes in itself is not a good predictor of risk as many diseases take several days to develop inside the mosquito and find their way to the mouthparts. This means that only older mosquitoes can pass on the infection. Mosquito age is therefore very important for assessing the effectiveness of anti-mosquito interventions but currently, there is no easy, accurate way of assessing the age of a mosquito population.Near-Infrared Spectroscopy (NIRS) is a new age-grading and species identification technique that has been developed in the laboratory. It predicts the age of the mosquito by measuring how a beam of light is reflected differently from the bodies of mosquitoes as they get older. Unlike other methods NIRS doesn't require costly chemicals or procedures and it can be carried out by anybody with minimal training. This makes it feasible for use as a routine method for monitoring mosquito age in the field. Currently NIRS cannot predict the age of an individual mosquito very accurately and tests have only been done on mosquitoes reared in the laboratory which are likely to be more uniform (and therefore give more accurate results) than those caught in the wild. However, for disease control it is more important to know the average age of the mosquito population than the age of individuals. Our preliminary work suggests that if we change the way we analyse NIRS outputs we can generate highly precise predictions of the average age of the mosquito population. The project intends to take NIRS from the laboratory to the field and test whether it is good enough to be able to be used in the routine monitoring of mosquito populations. The project will use semi-field and field data to operationalise the technique and outline how many mosquitoes need to be caught (and over how many days) to generate estimates accurate enough to guide the deployment of mosquito control.The work will concentrate on the two most important mosquito borne infections: malaria (which kills 438,000 people in 2015) and dengue (which infects 400 million people annually). However the technique developed here can be applied to other diseases and mosquito species. NIRS can also be used to differentiate closely-related mosquito species that are indistinguishable by eye. That is important, as not all of these mosquitoes have the same ability to transmit disease and are affected by control interventions differently. Similarly to age-grading, the capacity of NIRS to differentiate species needs to be more rigorously tested in the field. There is also evidence to suggest that NIRS might be able to detect whether a mosquito is infected with the virus that causes dengue disease. This will be tested for malaria, first in the laboratory in Burkina Faso and then in the field. Currently mosquito species, age and infection status are estimated using a variety of laborious and costly procedures that preclude their use as routine monitoring tools in poorer parts of the world. A single, inexpensive method for doing all three tests simultaneously would have significant public health impact: we could describe the risks of disease transmission and evaluate the efficacy of control programs far more cheaply and quickly.