Pathogens are microorganisms that have the potential to cause infectious diseases. Viruses, bacteria, protozoans and fungi are all potential pathogens. Pathogens are of different types and can spread through various means – usually skin contact, body fluids, or contact with contaminated surfaces. Some pathogens exist as airborne particles. The most common types of pathogens are viruses, bacteria, and fungi. Diseases caused by pathogens are many. Common examples of viral pathogens include common cold, yellow fever, flu, dengue fever etc.