Satterfield Dara A, Altizer Sonia, Williams Mary-Kate, Hall Richard J
Odum School of Ecology, University of Georgia, Athens, Georgia, United States of America.
Biological Sciences, University of Arkansas at Little Rock, Little Rock, Arkansas, United States of America.
PLoS One. 2017 Jan 18;12(1):e0169982. doi: 10.1371/journal.pone.0169982. eCollection 2017.
Many pathogens, including those infecting insects, are transmitted via dormant stages shed into the environment, where they must persist until encountering a susceptible host. Understanding how abiotic conditions influence environmental persistence and how these factors influence pathogen spread are crucial for predicting patterns of infection risk. Here, we explored the consequences of environmental transmission for infection dynamics of a debilitating protozoan parasite (Ophryocystis elektroscirrha) that infects monarch butterflies (Danaus plexippus). We first conducted an experiment to observe the persistence of protozoan spores exposed to natural conditions. Experimental results showed that, contrary to our expectations, pathogen doses maintained high infectivity even after 16 days in the environment, although pathogens did yield infections with lower parasite loads after environmental exposure. Because pathogen longevity exceeded the time span of our experiment, we developed a mechanistic model to better explore environmental persistence for this host-pathogen system. Model analysis showed that, in general, longer spore persistence led to higher infection prevalence and slightly smaller monarch population sizes. The model indicated that typical parasite doses shed onto milkweed plants must remain viable for a minimum of 3 weeks for prevalence to increase during the summer-breeding season, and for 11 weeks or longer to match levels of infection commonly reported from the wild, assuming moderate values for parasite shedding rate. Our findings showed that transmission stages of this butterfly pathogen are long-lived and indicated that this is a necessary condition for the protozoan to persist in local monarch populations. This study provides a modeling framework for future work examining the dynamics of an ecologically important pathogen in an iconic insect.
许多病原体，包括那些感染昆虫的病原体，是通过进入环境中的休眠阶段进行传播的，它们必须在环境中持续存在，直到遇到易感宿主。了解非生物条件如何影响病原体在环境中的持久性以及这些因素如何影响病原体传播，对于预测感染风险模式至关重要。在此，我们探讨了环境传播对一种感染帝王蝶（黑脉金斑蝶）的衰弱原生动物寄生虫（奥氏微孢子虫）感染动态的影响。我们首先进行了一项实验，以观察暴露于自然条件下的原生动物孢子的持久性。实验结果表明，与我们的预期相反，即使在环境中放置16天后，病原体剂量仍保持高感染性，尽管病原体在环境暴露后产生的感染其寄生虫负荷较低。由于病原体的存活时间超过了我们实验的时间跨度，我们开发了一个机理模型，以更好地探索这个宿主 - 病原体系统在环境中的持久性。模型分析表明，一般来说，孢子存活时间越长，感染率越高，帝王蝶种群规模略小。该模型表明，在夏季繁殖季节，落在马利筋植物上的典型寄生虫剂量必须至少存活3周，感染率才会增加；假设寄生虫释放率为中等值，要达到野外常见的感染水平，则需存活11周或更长时间。我们的研究结果表明，这种蝴蝶病原体的传播阶段寿命很长，这表明这是原生动物在当地帝王蝶种群中持续存在的必要条件。本研究为未来研究一种标志性昆虫中一种具有生态重要性的病原体的动态提供了一个建模框架。
