Which of the following is a common cause of pathogenic diseases?

Pathogenic diseases can be caused by a variety of microorganisms that invade the body and disrupt normal functions. Both bacteria and viruses are well-known agents that lead to infections and diseases, as they can multiply quickly and evade the immune system, causing a wide range of illnesses. For instance, bacteria can infect tissues and produce toxins, while viruses can hijack host cells to replicate and spread.

In addition to bacteria and viruses, fungi and parasites are also significant contributors to pathogenic diseases. Fungi can lead to infections ranging from mild skin conditions to serious systemic diseases, particularly in immunocompromised individuals. Parasites, such as protozoa and helminths, can inhabit the human body and cause diseases that vary in severity and symptoms.

Considering the roles that both groups of pathogens play in causing diseases, identifying them together emphasizes the diverse nature of infectious agents. Hence, the inclusion of both bacteria and viruses alongside fungi and parasites makes the option that combines all these categories the most comprehensive answer, addressing the multifaceted nature of pathogens responsible for diseases.