Microsporidia-host interactions in beneficial arthropods: Factors that influence chronic disease

微孢子虫是一种形成孢子的真核病原体，可在广泛的无脊椎动物和脊椎动物宿主中引起慢性感染。根据感染宿主的不同，这些病原体会造成经济损失，并具有兽医和医学重要性。微孢子虫生活在宿主细胞内，完全依赖宿主生存。这些病原体缺乏功能性线粒体，其基因组减少导致许多代谢途径的丧失。因此，微孢子虫的繁殖和生存需要宿主能量。 从有益的节肢动物中描述微孢子虫的频率正在增加，这些节肢动物既能在自然界中提供害虫控制，也能在生物防治项目中作为天敌大规模饲养。虽然微孢子虫被定义为病原体(在对宿主不利的情况下生长和发展的生物体)，但最近的研究表明，微孢子虫并不总是对宿主适合性造成负面影响。在某些情况下，微孢子虫会导致慢性衰弱疾病，而其他相关宿主似乎没有受到影响，即使病原体能够利用后者来发展和增殖。微孢子虫在某些宿主中能够成为成功的病原体，而在其他相关宿主中仍然不成功，其特征/因素仍然知之甚少。 这项拟议研究的目的是评估一些可能与病原体成功相关并最终可能影响慢性病影响的因素。我们过去的工作集中在用于生物防治的有益昆虫中微孢子虫的鉴定和相互作用，最近包括在几种瓢虫物种中的微孢子虫病原体。我们最近的研究为微孢子虫的宿主特异性和宿主-病原体效应提供了一些见解。在瓢虫体内，微孢子虫似乎具有相对广泛的寄主范围，通常对幼虫的发育有显著的影响，而对成虫没有明显的有害影响。此外，微孢子虫对一些瓢虫物种的影响很深，而其他与之密切相关的物种似乎没有受到影响。在某些情况下，后者充满微孢子虫孢子(证据表明它们是病原体的合适宿主)，甚至在不受影响的情况下传播病原体。因为微孢子虫被指定为严格意义上的病原体，所以问题仍然是这些病原体在它们感染的许多宿主中发挥什么作用，以及是什么使微孢子虫在一些宿主中成为成功的病原体，而在另一些宿主中保持相当良性的。 这项拟议的研究将侧重于可能影响微孢子虫作为导致慢性病的病原体的成功的因素。这些包括(1)胁迫对病原体和疾病进展的影响，(2)多重感染(每个寄主超过一个病原体)对疾病发展和寄主适合性的影响，以及(3)瓢虫体内的次生防御化学物质(生物碱)对病原发育和寄主适合性的作用。 在这项研究中获得的信息将有助于我们目前对疾病家畜和慢性病在调节有益节肢动物种群中所起的作用的理解。我们对慢性病的更多了解是重要的，有助于确保有益的节肢动物仍然是农业中化学虫害防治的可行替代方案。此外，微孢子虫感染在人类中正变得越来越常见，主要是那些免疫系统受损的人。因此，微孢子虫是医学上日益重要的新兴病原体。

Microsporidia are spore forming, eukaryotic pathogens that cause chronic infections in a wide range of invertebrate and vertebrate hosts. Depending on the host infected, these pathogens cause economic loss and are of veterinary and medical importance. Microsporidia live inside host cells and are fully dependent on their hosts for survival. These pathogens lack functional mitochondria and their reduced genome has resulted in the loss of many metabolic pathways. As a result, microsporidia require host energy for their reproduction and survival. Microsporidia are being described with increased frequency from beneficial arthropods, both those that provide pest control in nature and those that are mass-reared for use as natural enemies in biological control programs. Although microsporidia are defined as pathogens (organisms that grow and develop at the detriment of the host), recent studies have shown that microsporidia do not always cause negative effects with respect to host fitness. In some cases, microsporidia cause chronic debilitating disease, whereas other related hosts remain seemingly unaffected even though the pathogen is able to exploit the latter for its development and proliferation. The characteristics/factors that permit microsporidia to be successful pathogens in some hosts, while remaining unsuccessful in other related hosts, remains poorly understood. The purpose of this proposed study is to evaluate some of the factors that may be associated with pathogen success and could ultimately influence the impact of chronic disease. Our past efforts have focused on the identification and interaction of microsporidia in beneficial insects used for biological pest control, recently including microsporidian pathogens among several lady beetle species. Our more current studies have provided some insight on host specificity of microsporidia and host-pathogen effects. Microsporidia seem to have a relatively broad host range in lady beetles, oftentimes having pronounced effects on larval development while having no observable, detrimental effect on adults. Furthermore, microsporidia affect some lady beetle species profoundly whereas others closely-related species seem to remain unaffected. In some cases, the latter become filled with microsporidian spores (evidence that they serve as a suitable host for the pathogen) and even transmit the pathogen while remaining unaffected. Because microsporidia are designated as pathogens in the strict sense, the question remains as to what role these pathogens play in the many hosts that they infect and what enables microsporidia to become successful pathogens in some hosts while remaining rather benign in others. The proposed study will focus on factors that may influence the success of microsporidia as pathogens that cause chronic disease. These include (1) the impact of stress on the pathogen and disease progression, (2) the effects of multiple infections (more than one pathogen per host) on disease development and host fitness, and (3) the role secondary defense chemicals (alkaloids) in lady beetles on pathogen development and host fitness. Information gained during this study will help contribute toward our current understanding of disease epizootics and the role that chronic disease plays in the regulation of beneficial arthropod populations. Our increased understanding of chronic disease is important to help ensure that beneficial arthropods remain a viable alternative to chemical pest control in agriculture. Furthermore, microsporidia infections are becoming more common in humans, primarily those with a compromised immune system. As a result, microsporidia are emerging pathogens of increasing medical importance.