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The role of transmission in the evolution of virulence of parasitic helminths of domestic animals.

机译：传播在家畜寄生蠕虫毒力演变中的作用。

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摘要

Parasitic worms (macroparasites) cause serious disease in humans and other animals worldwide, and worm infections cause large losses in the production of food animals. Nevertheless, the ultimate causation of virulence (harm to the host) in these organisms has not been studied. The evolution of virulence in microparasites like bacteria and viruses has been extensively studied, and it is thought that transmission is intimately related to virulence in these organisms. Increased transmission in microparasites generally results in higher virulence, but if increased virulence, in the form of host death or reduced motility, decreases the overall transmission rate of the pathogen, the trade-off between transmission and virulence results in an optimal level of virulence for a given host-parasite interaction.; This study investigates the factors involved in the evolution of virulence in worms. The species studied are strongylid nematode parasites that live within the gastrointestinal tract of horses or sheep. The objective of this study is to test the “transmission hypothesis” in an effort to determine whether worm virulence results in a trade-off similar to that suggested for microparasites. Comparison of initial estimates of transmission (an index based on offspring production and survival), and virulence (based on estimates of the number of worms that generally cause host death), suggested that the trade-offs between virulence and transmission differ in parasites with different developmental strategies. There is a direct trade-off between transmission and virulence in parasite species that cause disease as reproductively mature adults (Trichonematidic development), but no relationship between transmission and virulence in parasite species where immature stages of the parasite cause the majority of pathology (Strongylidic development).; The development of a stage-structured demographic model that incorporated seasonal variations in parasite and host biology allowed for a more comprehensive estimate of transmission rate in Trichonematidic worms. In addition, analysis of experimental infections allowed for a better estimate of worm virulence. Regression analysis of virulence and transmission rates for parasites that are phylogenetically closely related and which exhibit similar modes of transmission suggested that there was, in fact, no trade-off between transmission and virulence. Other components of the parasites' biology were also examined, and it was determined that worm egg production is positively correlated with virulence. Although fecundity is highest in the most virulent worms, low survival and development of the infective stages of these organisms resulted in transmission rates that were not significantly different from those of less virulent worm species. These data do not support the transmission hypothesis suggested for microparasites, and suggest that virulence is de-coupled from transmission in the trichostrongylid nematodes of sheep.
机译：寄生蠕虫（宏寄生虫）在全世界范围内对人类和其他动物造成严重疾病，蠕虫感染在食用动物的生产中造成大量损失。然而，尚未研究这些生物中毒力的最终因果关系（对宿主的伤害）。在诸如细菌和病毒的微寄生物中，毒力的演变已被广泛研究，并且认为传播与这些生物中的毒力密切相关。微寄生虫传播的增加通常会导致更高的毒力，但是如果毒力增加（以宿主死亡或运动性降低的形式）降低了病原体的总体传播速率，则在传递和毒力之间进行权衡会导致最佳的毒力水平。给定的宿主-寄生虫相互作用。这项研究调查了蠕虫中毒力的进化所涉及的因素。研究的物种是生活在马或绵羊胃肠道中的强线虫线虫寄生虫。这项研究的目的是检验“传播假说”，以确定蠕虫毒力是否导致与微寄生虫类似的权衡。对传播的初步估计（基于后代生产和生存的指数）和毒力（基于通常导致宿主死亡的蠕虫数量的估计）的比较表明，毒力和传播之间的权衡取舍于具有不同寄生虫的寄生虫发展策略。在寄生虫物种的传播和毒力之间存在直接的权衡，这些疾病会导致成年生殖成年的疾病（毛发线虫病的发展），但在寄生虫物种的传播和毒力之间没有关系，在这种情况下，寄生虫的未成熟阶段会导致大部分病理（致鞭虫病的发展） ）。结合寄生虫和宿主生物学的季节性变化的阶段结构的人口统计学模型的发展，可以更全面地估计毛孔线虫蠕虫的传播速率。此外，对实验感染的分析可以更好地估计蠕虫的毒力。在系统发育上密切相关且显示相似传播模式的寄生虫的毒力和传播速率的回归分析表明，实际上，在传播和毒力之间没有权衡取舍。还检查了寄生虫生物学的其他组成部分，并确定蠕虫卵的产生与毒力呈正相关。尽管在最具毒性的蠕虫中繁殖力最高，但是这些生物的低存活率和感染阶段的发展导致其传播速率与毒性较低的蠕虫物种的传播速率没有显着差异。这些数据不支持针对微寄生虫提出的传播假说，并表明毒力与绵羊毛线虫线虫中的传播脱钩。

著录项

  • 作者

    Medica, Darcy Lynn.;

  • 作者单位

    Rutgers The State University of New Jersey - New Brunswick.;

  • 授予单位 Rutgers The State University of New Jersey - New Brunswick.;
  • 学科 Agriculture Animal Pathology.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 p.1098
  • 总页数 137
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 动物医学（兽医学）;
  • 关键词

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