Hostpathogen

Host-pathogen refers to the interaction between a host organism and a pathogenic agent that can cause disease. In this relationship the pathogen gains resources and a niche for replication, while the host mounts defenses to limit invasion, replication, and spread. Outcomes range from asymptomatic carriage to acute illness, chronic infection, or mortality, depending on the traits of the pathogen and the response of the host.

Pathogens include bacteria, viruses, fungi, protozoa, helminths, and prions. Hosts span many life forms, including humans, domestic animals, wildlife, crops, and other plants. Interactions are influenced by pathogen characteristics such as virulence, tissue tropism, and transmission mode, and by host factors such as genetics, immune status, microbiome composition, age, and prior exposures. The relationship can be commensal, where the pathogen causes little harm, or pathogenic, where disease occurs, with various degrees of severity. Some infections are acute, others latent, chronic, or recurrent.

Infection typically involves exposure, colonization, replication, and potential transmission to new hosts. Transmission routes include direct contact, aerosols, vectors, contaminated surfaces, and environmental reservoirs. Hosts employ barriers (skin and mucous membranes), innate immune responses, and adaptive immunity to detect and clear infections; pathogens may counter with immune evasion strategies such as antigenic variation, immune modulation, or hiding in reservoirs.

Understanding host-pathogen dynamics supports public health, medicine, and agriculture by guiding vaccination, treatment, infection control, and risk assessment. Notable examples span a wide range of organisms and diseases, illustrating the diversity and complexity of host-pathogen interactions.