Infectious Diseases: Pathogens, Transmission and Control | 传染病：病原体、传播与控制

📚 Infectious Diseases: Pathogens, Transmission and Control | 传染病：病原体、传播与控制

Infectious diseases are caused by pathogens such as bacteria, viruses, protoctists and fungi that can spread from one host to another. Understanding their transmission and control is a core topic in the Cambridge International A Level Biology syllabus, especially cholera, malaria, tuberculosis, HIV/AIDS and measles.

传染病是由细菌、病毒、原生生物和真菌等病原体引起并可在宿主之间传播的疾病。理解其传播与控制是剑桥国际 A Level 生物课程的核心内容，尤其是霍乱、疟疾、肺结核、艾滋病和麻疹等疾病。

1. What is an Infectious Disease? | 什么是传染病？

A disease is a condition in which the body or part of the body does not function normally. Diseases are broadly divided into infectious and non-infectious types. Infectious diseases are caused by living or non-living pathogens that can be transmitted from one individual to another, directly or indirectly.

疾病是指身体或身体某部分功能异常的状态。疾病大致分为传染性疾病和非传染性疾病。传染病由可从一个个体直接或间接传播到另一个个体的有生命或无生命的病原体引起。

Non-infectious diseases include inherited disorders such as cystic fibrosis, nutritional deficiency diseases such as scurvy, and many cancers. They are not passed from person to person by pathogens.

非传染病包括囊性纤维化等遗传病、坏血病等营养缺乏病以及许多癌症。它们不通过病原体在人与人之间传播。

Infectious diseases range from mild, self-limiting infections such as the common cold to life-threatening diseases such as tuberculosis and malaria. A key feature is that the pathogen must be transmitted, survive in the host, and often evade or damage host defences.

传染病包括普通感冒等轻微自限性感染以及肺结核和疟疾等危及生命的疾病。其关键特征是病原体必须能够传播、在宿主体内存活，并往往逃避或破坏宿主防御。

2. Types of Pathogen | 病原体的类型

The main groups of pathogen are bacteria, viruses, protoctists (protozoa) and fungi. Bacteria are prokaryotic cells, usually 0.5-5 μm in diameter, that can reproduce rapidly by binary fission. Examples include Vibrio cholerae and Mycobacterium tuberculosis.

病原体主要分为细菌、病毒、原生生物（原生动物）和真菌。细菌是原核细胞，直径通常为 0.5-5 μm，可通过二分裂快速繁殖。例如霍乱弧菌和结核分枝杆菌。

Viruses are non-cellular infectious particles made of a nucleic acid core (DNA or RNA) surrounded by a protein capsid, sometimes with a lipid

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