A pathogen is any microorganism that causes disease in a host. Pathogens include bacteria, viruses, fungi, and parasites. Enzymes are proteins that speed up chemical reactions and are not microorganisms. Immune factors are components of the immune system that protect against disease. A vector is an organism, such as a mosquito or tick, that transmits pathogens but does not itself cause disease. The NEX Science exam commonly assesses understanding of infectious disease terminology and distinctions between disease-causing organisms and disease carriers. Recognizing pathogens as the direct cause of illness is a key concept in microbiology and public health.
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