Evaluation of rodent control to fight Lassa fever based on field data and mathematical modelling

The Natal multimammate mouse (<i>Mastomys natalensis</i>) is the reservoir host of Lassa virus, an arenavirus that causes Lassa haemorrhagic fever in humans in West Africa. Because no vaccine exists and therapeutic options are limited, preventing infection through rodent control and human behavioural measures is currently considered to be the only option. In order to assess the efficacy of rodent control, we performed a 4-year field experiment in rural Upper Guinea and developed a mathematical model to simulate different control strategies (annual density control, continuous density control, and rodent vaccination). For the field study, rodenticide baits were placed each year in three rural villages, while three other villages were used as controls. Rodents were trapped before and after every treatment and their antibody status and age were determined. Data from the field study were used to parameterize the mathematical model. In the field study, we found a significant negative effect of rodent control on seroprevalence, but this effect was small especially given the effort. Furthermore, the rodent populations recovered rapidly after rodenticide application, leading us to conclude that an annual control strategy is unlikely to significantly reduce Lassa virus spillover to humans. In agreement with this finding, the mathematical model suggests that the use of continuous control or rodent vaccination is the only strategy that could lead to Lassa virus elimination. These field and model results can serve as a guide for determining how long and frequent rodent control should be done in order to eliminate Lassa virus in rural villages.

奈氏多乳鼠（Natal multimammate mouse，学名*Mastomys natalensis*）是拉沙病毒（Lassa virus）的储存宿主，该病毒属于沙粒病毒科（arenavirus），可在西非引发人类拉沙出血热。由于目前尚无可用疫苗，且治疗手段有限，通过啮齿动物防控与人类行为干预阻断感染，是当前公认的唯一可行防控方案。为评估啮齿动物防控的实际效果，研究团队在上几内亚乡村地区开展了为期4年的野外实验，并构建数学模型以模拟三类防控策略：年度密度防控、持续密度防控以及啮齿动物疫苗接种。在野外研究阶段，团队每年在3个乡村布设灭鼠剂（rodenticide）饵料，另外3个村庄作为空白对照。每次防控措施实施前后均会捕捉啮齿动物，并检测其抗体状态与年龄。野外研究获取的实验数据被用于该数学模型的参数校准。野外研究结果显示，啮齿动物防控对血清阳性率（seroprevalence）存在显著负向影响，但该影响幅度较小，尤其考虑到防控投入的人力与物力成本。此外，灭鼠剂施用后啮齿动物种群会快速恢复，由此研究团队得出结论：年度防控策略不太可能显著降低拉沙病毒向人类的跨种溢出风险。与该实验发现一致的是，数学模型模拟结果表明，唯有持续防控或啮齿动物疫苗接种策略，方可实现拉沙病毒的根除。本项野外实验与模型研究结果，可为乡村地区根除拉沙病毒所需的啮齿动物防控时长与频率提供科学参考依据。