Transmission, infection, and pathogenesis

Transmission is a key process for parasites. Different routes (e.g. faecal–oral) and modes (e.g. by aerosols or vectors) exist. A major context is vertical (to offspring) or horizontal (all other) transmission. All components of the transmission process evolve. Successful transmission includes the infection of a new host. Macroparasites typically infect as individuals, but microparasites need an infective dose. Doses vary enormously among parasites. Various models describe variation in infective dose. Process-based models assume random colonization, co-operative parasite manipulation, or are focused on early dynamics. With the processes of pathogenesis (e.g. tissue destruction, reducing host capacities), damage to the host emerges. Virulence factors are important mediators of parasite success and often involved in host manipulation and pathogenesis, including immunopathology.