Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK; Institute of Infection and Global Health, University of Liverpool, Leahurst Campus, Neston, CH64 7TE, UK.
Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK.
Epidemics. 2019 Sep;28:100352. doi: 10.1016/j.epidem.2019.100352. Epub 2019 Jul 15.
Many pathogens of conservation concern circulate endemically within natural wildlife reservoir hosts and it is imperative to understand the individual and ecological drivers of natural transmission dynamics, if any threat to a related endangered species is to be assessed. Our study highlights the key drivers of infection and shedding dynamics of squirrelpox virus (SQPV) in its reservoir grey squirrel (Sciurus carolinensis) population. To clarify SQPV dynamics in this population, longitudinal data from a 16-month mark-recapture study were analysed, combining serology with real-time quantitative PCR to identify periods of acute viraemia and chronic viral shedding. At the population level, we found SQPV infection prevalence, viral load and shedding varied seasonally, peaking in autumn and early spring. Individually, SQPV was shown to be a chronic infection in >80% of grey squirrels, with viral loads persisting over time and bouts of potential recrudescence or reinfection occurring. A key recurring factor significantly associated with SQPV infection risk was the presence of co-infecting squirrel adenovirus (ADV). In dual infected squirrels, longitudinal analysis showed that prior ADV viraemia increased the subsequent SQPV load in the blood. However, there was a strong, negative association between prior ADV viraemia and subsequent SQPV shedding from the forearm, probably caused by ADV prolonging the SQPV acute viraemic phase, so delaying onset of the chronic shedding phase, and thereby altering viral shedding patterns over the time scales examined here. Hence, co-circulating ADV infection may be involved in mediating both the quantitative levels of SQPV infection and the timing and degree of subsequent infectiousness of grey squirrels.
许多具有保护意义的病原体在野生动物宿主中地方性流行，因此，了解自然传播动态的个体和生态驱动因素至关重要，如果要评估任何对相关濒危物种的威胁。我们的研究强调了松鼠痘病毒（SQPV）在其天然宿主灰松鼠（Sciurus carolinensis）种群中感染和脱落动态的关键驱动因素。为了阐明该种群中的 SQPV 动态，我们对一项为期 16 个月的标记-重捕研究的纵向数据进行了分析，将血清学与实时定量 PCR 相结合，以确定急性病毒血症和慢性病毒脱落的时期。在种群水平上，我们发现 SQPV 感染率、病毒载量和脱落率呈季节性变化，在秋季和早春达到高峰。个体层面上，超过 80%的灰松鼠存在 SQPV 慢性感染，病毒载量随时间持续存在，且存在潜在复发或再感染的情况。一个与 SQPV 感染风险显著相关的关键反复出现的因素是同时感染的松鼠腺病毒（ADV）。在双重感染的松鼠中，纵向分析表明，先前的 ADV 病毒血症会增加随后血液中 SQPV 的载量。然而，先前的 ADV 病毒血症与随后从前臂脱落的 SQPV 之间存在强烈的负相关，这可能是由于 ADV 延长了 SQPV 的急性病毒血症阶段，从而延迟了慢性脱落阶段的开始，并改变了在此处检查的时间尺度上的病毒脱落模式。因此，共同循环的 ADV 感染可能参与调节 SQPV 感染的定量水平以及灰松鼠随后的传染性的时间和程度。
