Pathogen

Definition

An organism, agent, or micro-organism capable of causing disease in a host. In arthropod contexts, pathogens include viruses, bacteria, fungi, protozoa, and nematodes that infect insects, arachnids, or other invertebrates, as well as arthropod-vectored pathogens that transmit disease to vertebrates. The term encompasses obligate parasites, opportunistic infections, and entomopathogens used in biological control.

Etymology

From Greek pathos (suffering, disease) + -genes (producer of)

Example

Beauveria bassiana, an entomopathogenic fungus, serves as a biological control pathogen that infects and kills pest insects such as whiteflies and aphids by penetrating the cuticle and proliferating within the hemocoel.

Synonyms

• infectious agent
• disease agent
• etiologic agent

Related Terms

• entomopathogen
• Vector
• Host
• Parasite
• Virulence
• Infection
• biological control agent
• Zoonosis

Usage Notes

Distinguished from parasite by emphasis on disease causation rather than nutritional dependence; some organisms function as both. In entomology, 'entomopathogen' is preferred for insect-specific pathogens. Virulence and pathogenicity vary with host condition, environment, and pathogen strain. The term is broader than 'germ' (often restricted to microbes) and more specific than 'causal agent' (which may include non-living factors).