Infections occur when what invade the body?

The correct answer is pathogens. Infections occur when pathogens invade the body. Pathogens are microorganisms that cause disease, and they include a wide variety of agents such as bacteria, viruses, fungi, and parasites. When these pathogens enter the body, they can disrupt normal bodily functions, leading to infection and illness.

Understanding the role of pathogens is crucial in infection control, as healthcare providers work to prevent and manage infections by addressing these harmful invaders. This knowledge helps in recognizing the symptoms of infections and responding appropriately to protect both patients and healthcare personnel.

The other options focus either on a specific type of invader or do not encompass the full range of infectious agents. Cells alone do not indicate an invasion that causes infections; instead, they represent the building blocks of tissue. The mention of microorganisms is too narrow because not all microorganisms are pathogenic; many are harmless or even beneficial. Limiting the choice to viruses only excludes other significant pathogens such as bacteria and fungi, which also play a critical role in the development of infections. Therefore, pathogens encompass all potential invaders responsible for infectious diseases, making this the most accurate answer.