Pathogen transmission

Transmission is defined as the transfer of a pathogen that causes communicable disease from an infected host individual or group to another individual or group, regardless of whether the other individual has previously been affected. The phrase refers to the direct transmission of germs from one person to another through one or more of the following methods:

Airborne transmission

Very small dry and wet particles that linger in the air for long periods of time, allowing contamination to spread even after the host has left. Particle size is less than 5 μm.

Droplet transmission refers to the movement of small, usually wet particles through the air for a brief period of time. Contamination is most common when the host is present. Particles with a diameter greater than 5 μm.

Direct physical contact

Physical interaction with an infected person, including sexual contact

Indirect physical contact

Most commonly through touching a contaminated surface, such as soil (fomite) faecal contamination

Oral transmission

Generally from unclean hands, contaminated food or water sources due to a lack of sanitation and hygiene, this is a common mode of infection in paediatrics, veterinary medicine, and impoverished countries.

Indirect transmission can also occur through another organism, such as a vector (such as a mosquito or fly) or an intermediary host (e.g. Humans can contract tapeworm from pigs if they eat undercooked meat). Indirect transmission may be caused by zoonoses or, more commonly, bigger pathogens such as macroparasites with more complicated life cycles. Transmissions can be autochthonous (that is, between two people in the same location) or involve the microorganism or the affected hosts travelling.

An infectious disease agent can be transmitted horizontally (by licking, touching, biting) or vertically (by passing the agent causing the disease 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 through air – cough or sneeze (vectors or fomites that allow the transmission of the disease-causing pathogen without physical contact).

The term infectivity refers to an organism’s ability to enter, survive, and reproduce in its host, whereas infectiousness refers to the ease with which a disease agent can be transmitted to additional hosts. Pathogens can be transmitted through direct contact, contaminated food, body fluids, or items, airborne inhalation, or vector organisms.

The probability of infection when an infected host comes into touch with a noninfected host is known as transmissibility.

Community transmission occurs when the source of infection for the spread of an illness is unknown or when there is no relationship in terms of patient-to-patient contact. Beyond proven cases, it refers to the difficulty in grasping the epidemiological link in the population.

The source of the virus has been located within the reporting place, which is known as local transmission (such as within a country, region or city).