Transmission is the process by which an infectious agent spreads from an infected host or reservoir to a new susceptible host.
Modes and Significance
Transmission mechanisms are varied and underpin the field of epidemiology. Direct transmission involves immediate transfer of pathogens through physical contact, sexual intercourse or respiratory droplets expelled during coughing or sneezing. Indirect transmission occurs when microorganisms are conveyed via contaminated water, food, fomites or biological vectors. Airborne transmission refers to the spread of pathogens in aerosolized particles that remain suspended and can travel beyond close contact distances. Vector-borne transmission involves arthropods such as mosquitoes, ticks and fleas that acquire pathogens during feeding and pass them to subsequent hosts. Vertical transmission describes the passage of pathogens from mother to offspring during pregnancy, delivery or breastfeeding. The efficiency of transmission is influenced by pathogen load, environmental persistence, host behavior and immunity. Understanding these routes enables the design of interventions such as vaccination programs, sanitation improvements, vector control, quarantine and behavioral changes. Epidemiological models use transmission parameters to predict outbreak dynamics and assess control strategies, while infection prevention policies in healthcare settings are based on knowledge of transmission pathways.
Modes in Action
Malaria is transmitted by Anopheles mosquitoes, which ingest Plasmodium parasites from an infected individual and later inject them into new hosts. Influenza spreads primarily via respiratory droplets generated by coughing or talking, highlighting the importance of masks and physical distancing during outbreaks. Cholera is contracted through ingestion of water or food contaminated with Vibrio cholerae. Lyme disease results from the bite of Ixodes ticks carrying Borrelia burgdorferi. Human immunodeficiency virus can be transmitted through sexual contact, exposure to infected blood or vertical transmission from mother to child. Rabies virus spreads through bites from infected mammals. These examples illustrate how diverse transmission routes dictate the spread and control of infectious diseases.
Transmission pathways define the ecological and epidemiological landscape of pathogens. Recognizing how microorganisms spread allows for targeted interventions and informs global health strategies. Mitigating transmission remains central to preventing disease emergence and outbreaks.
Related Terms: infection, vector, host, contagion, epidemiology