virulencije

Virulence, or virulences in some languages, describes the degree to which a pathogen can cause disease in a host. It includes both the severity of illness and the ability to overcome host defenses. Virulence is not fixed; it results from interactions among pathogen traits, host susceptibility, and environmental conditions.

Virulence is driven by virulence factors—molecules or structures that enhance invasion, replication, spread, and immune evasion. Examples include toxins, tissue-degrading enzymes, adhesins and invasins, capsules that resist phagocytosis, and secretion systems that deliver effectors into host cells. Nutrient acquisition, such as iron uptake, also contributes.

Measurement of virulence often uses experimental or epidemiological indicators. Infectious dose or lethal dose in model systems, case severity, case fatality, and transmission potential are common assessments, though ethical constraints limit some approaches. In practice, virulence is a context-dependent property.

Host factors such as age, prior immunity, genetics, microbiome composition, and co-infections, along with the inoculum size and route of entry, influence outcomes. Pathogens may evolve virulence traits in response to host defenses and public health interventions, balancing the benefits of causing disease against the need to spread.

Understanding virulence helps in developing vaccines and therapies, predicting outbreak dynamics, and designing surveillance strategies. It emphasizes that disease severity emerges from a complex interplay of pathogen, host, and environment.