Spread of disease

In medicine, public health, and biology, transmission is the passing of a pathogen causing communicable disease from an infected host individual or group to a particular individual or group, regardless of whether the other individual was previously infected.

The term strictly refers to the transmission of microorganisms directly from one individual to another by one or more of the following means:

Transmission can also be indirect, via another organism, either a vector (e.g. a mosquito or fly) or an intermediate host (e.g. tapeworm in pigs can be transmitted to humans who ingest improperly cooked pork). Indirect transmission could involve zoonoses or, more typically, larger pathogens like macroparasites with more complex life cycles. Transmissions can be autochthonous (i.e. between two individuals in the same place) or may involve travel of the microorganism or the affected hosts.

An infectious disease agent can be transmitted in two ways: as horizontal disease agent transmission from one individual to another in the same generation (peers in the same age group). by either direct contact (licking, touching, biting), or indirect contact air – cough or sneeze (vectors or fomites that allow the transmission of the agent causing the disease without physical contact). or by vertical disease transmission, passing the agent causing the disease from parent to offspring, such as in prenatal or perinatal transmission.

...
Wikipedia