Which of the following describes protozoal infections?

Protozoal infections are characterized by the invasion of the body by single-celled parasitic organisms. Protozoa are microscopic, often motile organisms that can invade various tissues in the body, leading to a range of diseases. Examples include malaria, which is caused by the Plasmodium species, and Giardia, which can lead to gastrointestinal issues. Understanding this definition is crucial for identifying and addressing various health conditions related to these pathogens.

The other options describe different categories of infections: multicellular worms are associated with helminth infections, viruses refer to infections caused by viral pathogens, and contact with contaminated surfaces pertains to infections spread by bacteria or fungi, not protozoa. Each of these categories has distinct characteristics and paths of transmission, highlighting the unique nature of protozoal infections.