diseasetransmission

Disease transmission refers to the mechanism by which an infectious agent passes from an infected or contaminated source to a susceptible host, leading to infection or disease. Transmission can occur directly from person to person or indirectly through the environment, objects, or vectors.

Common transmission routes include direct contact (physical transfer between people), indirect contact via fomites, droplets produced by coughing or sneezing, and airborne transmission where small particles suspend in the air and can travel beyond close contact. Vector-borne transmission involves living organisms such as mosquitoes or ticks that carry pathogens from one host to another. Vehicle-borne transmission occurs through contaminated food, water, or other inanimate objects. Other routes include fecal-oral transmission and vertical transmission from mother to child.

Several factors influence transmission, including properties of the pathogen (infectious dose, environmental stability), host susceptibility and behavior (immunity, vaccination status, hygiene), and environmental conditions (crowding, ventilation, humidity). Population structure and social networks also affect how quickly a disease spreads.

Epidemiology uses quantities such as the basic reproduction number, R0, to describe the average number of secondary cases generated by a single infectious case in a fully susceptible population. The effective reproduction number reflects current immunity and interventions. Transmission patterns determine whether diseases are endemic, sporadic, or capable of causing outbreaks.

Prevention and control aim to break transmission chains and may include vaccination, hand hygiene and respiratory etiquette, physical distancing, masking, improved ventilation, isolation of cases, contact tracing, safe food and water practices, vector control, and surveillance.

Understanding transmission is a core component of public health, informing guidelines and interventions during outbreaks and informing risk communication and policy decisions.