What is a primary cause of infectious diseases?

Pathogenic microorganisms are the primary cause of infectious diseases because they include bacteria, viruses, fungi, and parasites that can invade the body and multiply, leading to illness. These microorganisms can be transmitted from person to person, through contaminated food or water, or via vectors like insects. When they enter the body, they can disrupt normal biological functions and provoke immune responses, which manifest as symptoms of disease.

Other options such as genetic mutations, environmental factors, and lifestyle choices can influence overall health and susceptibility to diseases but do not directly cause infectious diseases. While genetic mutations can affect how the body responds to infections, they do not create the pathogens themselves. Environmental factors might affect the prevalence or spread of infectious diseases, but they are not the direct cause. Similarly, lifestyle choices can influence health and immunity but are not the fundamental trigger for infections; rather, they set the stage for how well the body can resist or respond to infectious agents.