Types Of Disease Transmission
At a high level, all diseases are transmitted through two means — direct and indirect transmission.
Direct transmission is when an infectious agent is spread to a host directly from its reservoir. Infectious agents can be disease-causing bacteria, viruses, parasites, and other organisms. A host is any person or animal that is susceptible to getting infected by the agent.
Reservoirs are any person, animal, or habitat in which an infectious agent grows and multiplies. Hosts differ from reservoirs because hosts can get infected by an agent, while reservoirs do not.
Sexually-transmitted diseases like syphilis or genital warts are infections spread by direct transmission. Monkeypox, for example, can be spread through skin-to-skin contact with body fluids, rashes, and scabs on infected individuals or by kissing, hugging, and sex.
Indirect transmission of disease happens when an infectious agent is not transferred directly from a reservoir to a host. In this category, there is no direct person-to-person interaction to spread the disease. The means of indirect disease transmission include contaminated air, food, water, soil, animals as intermediate vectors, and more. Indirect transmission of disease is possible through:
- The air
- Blood, urine, and other body fluids
- Sexual activity
- Contact with contaminated material, including bedding, medical equipment, and more.
Examples of direct transmission include COVID-19, influenza, and other respiratory diseases that can be spread between people through contaminated droplets in the air. Monkeypox can be spread through direct skin-to-skin contact and indirect transmission through contaminated fabric, surfaces, and more.
Tick-borne diseases like Lyme disease, ehrlichiosis, babesiosis, Rocky Mountain spotted fever, Powassan fever, Tularemia, and more spread through indirect transmission. Malaria and dengue are transmitted indirectly through contaminated water and mosquitoes as vectors.