How Do Diseases Spread?: How To Train Epidemiology Students

Types Of Disease Transmission

At a high level, all diseases are transmitted through two means — direct and indirect transmission. 

Direct 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

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 
• Feces 
• 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.

Why Is It Important To Study The Spread Of Disease?

Learning about how diseases are spread is one of the most fundamental pillars of epidemiology and public health. Understanding disease transmission helps drive healthcare initiatives, public health resourcing and response, and prevention of outbreaks. The benefits of studying disease transmission include:

• Strategic R&D: Being able to prioritize research, vaccine, and treatment for diseases that have the highest potential for epidemics and pandemics
• Improve community health: Implement timely preventive measures for community health like vaccination drives, awareness-building, improving medical infrastructure, and healthcare outreach for high-risk populations
• Enhanced diagnostic tools: Develop more accurate diagnostic tools for infectious diseases 
• Facilitate early diagnosis: Train clinicians on emerging infectious diseases, zoonotic spillovers, or new variants so that they can make faster and more accurate diagnoses at the point of care
• Advance the field of epidemiology: Improve epidemiology courses and educate the next generation of epidemiologists and public health decision-makers.

Challenges Understanding Disease Spread

Trying to educate students on disease transmission can be quite difficult. There are hundreds of thousands of infectious diseases and disease-causing pathogens. Many of these infectious agents have complex life cycles involving multiple reservoirs, vectors, and hosts. Adding to the confusion, there are emerging infectious diseases to keep an eye on, and old pathogens with new variants, and the potential for new zoonotic spillovers. 

How can you engage your students’ interest in infectious disease transmission as a teacher?

While some level of rote memorization may be necessary, it is not always the most effective way for students to really learn. Students may not learn how to analyze and solve problems that cement their understanding of the course material. Instead, a mix of visual learning aids, interactive tools, and in-class activities can help enhance learning. 

To help educators prepare for their coursework, GIDEON offers lesson plans for a variety of subjects, including: 

• How infectious diseases spread
• The epidemiological triangle (or epidemiological triad)
• Bioterrorism and bioagents
• Identifying medically-important pathogens
• Vector-borne diseases
• Foodborne illnesses
• Vaccines and the history of vaccines

Use GIDEON lesson plans and case studies to help enhance your courses with engaging infectious disease content.