virulentnost

Virulentnost, or virulence, is a property of a pathogen describing its capacity to cause disease in a host. It reflects the severity of illness and the likelihood that infection will lead to clinically apparent disease. Virulence arises from specific traits, known as virulence factors, such as toxins, enzymes that facilitate tissue invasion, adhesins that promote attachment, capsules that resist phagocytosis, and mechanisms to evade or modulate the host immune response.

The expression of virulence is influenced by the pathogen’s genetics, the host’s immune status and genetics, and environmental conditions, including coinfections and stress.

Virulence is distinct from transmissibility. A pathogen may be highly virulent but poorly transmissible, or highly transmissible with modest virulence. Measuring virulence often involves experimental models that assess disease severity or mortality, such as dose–response relationships. In population biology, the concept is integrated with transmission potential; the trade-off between virulence and transmission can shape pathogen evolution.

Public health aims to reduce virulence impact through vaccination, antimicrobial therapy, and infection control. Some vaccines decrease virulence by preventing disease, while live-attenuated vaccines reduce the pathogen’s harmful effects. Understanding virulence helps in risk assessment, outbreak response, and the development of therapeutics.

Examples of virulence factors include toxins that disrupt host cells, enzymes that break down tissue barriers, and strategies to avoid detection by the immune system. Virulence varies among strains and species and can change over time due to evolution and ecological context.