A pathogen is a microorganism or infectious agent capable of causing disease in a host. Pathogens include a broad range of biological entities, such as bacteria, viruses, fungi, and parasites, that can invade and replicate within human, animal, or plant hosts and disrupt normal physiological functions.
A pathogen’s ability to cause disease depends on factors such as virulence, host susceptibility, and environmental conditions. Some pathogens, including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and various viral and parasitic species, are major contributors to global morbidity and mortality and are monitored closely due to their potential for outbreaks, antimicrobial resistance, and public health impact. Pathogens have their own genomes, and understanding pathogens and their interactions with hosts is essential for developing strategies for surveillance, prevention, diagnosis, and treatment of infectious diseases.