How Diseases Spread

The Mechanisms of Disease Transmission

Disease transmission occurs when an infectious agent, or pathogen, passes from a host organism to a new host.
Pathogens causing disease include bacteria, viruses, protozoa, fungi, and occasionally larger parasites.
There are four main methods of disease transmission: direct contact, indirect contact, droplet transmission, and vector-borne transmission.

Direct contact transmission involves physical contact between an infected person and a susceptible person, and the physical transfer of microorganisms.
This method often occurs through person-to-person contact, such as handshake, touch, or sexual intercourse.
It can also happen when an infected person touches their conjunctiva, nasal, or oral mucosa and then touches a susceptible person’s corresponding mucosa.

Indirect contact transmission involves contact of a susceptible host with a contaminated inanimate object, often called a fomite, in the environment of an infected person.
Common objects include doorknobs, writing utensils, touch screen interfaces, and toys in an infected person’s environment.

Droplet transmission happens when a person is in close contact (within 1 meter) with an infected person and exposure to potentially infective respiratory droplets occurs.
These droplets may be produced when an infected person coughs, sneezes, talks, or exhales.
The droplets can land on the surfaces of the mouth and nose of people who are nearby or possibly could be inhaled into the lungs.

Vector-borne transmission occurs when vectors (such as mosquitoes, ticks, or fleas) transmit an infectious pathogen from one host to another.
The vector contracts the disease from an infected host (which could be a human or animal) and subsequently infects a new host.
Common vector-borne diseases include malaria, Lyme disease, and dengue fever.

Hand hygiene, including hand washing with soap and water and use of alcohol-based hand sanitiser, is one of the most effective ways to prevent disease spread.
Immunisation against certain diseases can contribute to controlling disease spread.
Sound sanitation practices, good personal hygiene, regular cleaning of surfaces, and insect repellent can lower the risk of disease transmission.
Use of protective measures, like wearing a mask and social distancing, can also prevent droplet transmission.