From microbes to communities. From prevention to preparedness.
Infectious diseases are among humanity's oldest health challenges — yet they remain central to the future of global health. Explore how infections emerge, spread and affect people differently, and how vaccination, evidence, innovation, health systems, One Health and global cooperation can protect communities.
An infection may begin with a microorganism, but its consequences depend on much more: housing, nutrition, education, water and sanitation, climate, mobility, behaviour, healthcare access, surveillance, technology and the strength of health systems.
Understanding infectious disease means understanding both biology and the conditions that shape exposure, vulnerability, prevention, treatment and recovery.
Infectious diseases are caused by pathogenic organisms. Communicable diseases are infectious diseases that can be transmitted between hosts. Understanding this distinction helps us think accurately about transmission and prevention.
Diseases caused by pathogenic microorganisms such as bacteria, viruses, fungi and parasites.
Infectious diseases that can be transmitted directly or indirectly between hosts, including some infections that move between animals and humans.
All communicable diseases are infectious — but not all infectious diseases are communicable.
Tetanus is caused by Clostridium tetani. The organism can enter the body through contaminated wounds. Tetanus is therefore infectious, but it is not normally transmitted from person to person.
Transmission is not inevitable. Infectious-disease prevention often works by interrupting one or more links in the chain between an infectious agent and a susceptible host.
The microorganism capable of causing infection.
The environment or host in which an infectious agent normally lives and may multiply.
The route by which an infectious agent leaves its reservoir.
The mechanism by which an infectious agent reaches another host.
The route through which an infectious agent enters a new host.
A person or animal who may become infected depending on immunity, exposure and other factors.
Different pathogens have different transmission pathways. One disease may also have more than one route of transmission.
Some infections spread through respiratory particles or aerosols, especially during close or prolonged exposure.
Contaminated food and water can transmit many bacterial, viral and parasitic infections.
Vectors such as mosquitoes and ticks can transmit infectious agents between hosts.
Some infections can be transmitted through particular exposures to infected blood or body fluids.
Some infections can move between animals and humans.
Some infections are transmitted through sexual contact, with prevention depending on the specific infection.
Some pathogens persist in soil, water or other environments and can reach people through specific exposures.
Some diseases have more than one important transmission pathway or transmission context.
No single list can represent every infectious disease. These learning clusters provide a practical gateway into some of the diseases, disease groups and public-health challenges that matter globally.
Tuberculosis is caused by bacteria of the Mycobacterium tuberculosis complex. TB most commonly affects the lungs and can spread through the air when people with infectious pulmonary TB release infectious particles.
TB connects microbiology with poverty, housing, ventilation, diagnosis, treatment, drug resistance, health systems and equity.
HIV is a virus that attacks the immune system. Effective antiretroviral therapy can suppress the virus and allow people living with HIV to live healthy lives.
Why do stigma, discrimination, access to testing and treatment, and social conditions matter alongside biology?
Malaria is caused by Plasmodium parasites and is transmitted mainly through infected mosquitoes. It remains a major global health challenge, particularly in tropical and subtropical regions.
Parasites • Mosquitoes • Environment • Climate • Prevention • Diagnosis • Treatment • Equity
COVID-19 demonstrated how a respiratory pathogen can rapidly affect individuals, communities, economies and health systems. It also highlighted the importance of surveillance, scientific evidence, communication, vaccination and preparedness.
What should societies learn from the COVID-19 experience before the next major respiratory epidemic?
Influenza viruses can cause seasonal epidemics and, when novel viruses acquire the ability to spread efficiently between people, can create pandemic threats.
Surveillance • Laboratory capacity • Vaccines • Communication • Health-system readiness
Viral hepatitis is not one disease with one transmission route. Hepatitis A, B, C, D and E differ in how they spread, how they are prevented and how they are treated.
Human papillomavirus (HPV) is a very common infection. Certain HPV types can cause cancers, including cervical cancer. HPV vaccination is an important prevention strategy.
Vaccination + screening + appropriate follow-up can substantially reduce the burden of cervical cancer.
WHO recognizes a diverse group of neglected tropical diseases affecting populations that often experience poverty, limited access to healthcare, unsafe water and sanitation, and other structural disadvantages.
Schistosomiasis • Lymphatic filariasis • Onchocerciasis • Leishmaniasis • Trachoma • Soil-transmitted helminths • Chagas disease
Safe food and water are fundamental public-health protections. Foodborne illness can result from bacteria, viruses, parasites and other hazards.
Salmonella can cause gastrointestinal illness and can be transmitted through contaminated food and other exposure pathways.
Campylobacter is an important cause of bacterial gastroenteritis and is associated with contaminated food and animal sources.
Certain strains of E. coli can cause serious foodborne illness. Food safety and prevention of contamination are critical.
Listeria monocytogenes can cause serious illness, particularly in certain higher-risk populations.
Cholera is strongly connected to unsafe water, sanitation and hygiene conditions.
Typhoid fever is caused by Salmonella Typhi and is associated with contaminated food and water.
Hepatitis A and E can be associated with fecal-oral transmission and contaminated food or water.
Safe preparation, cooking, storage, hygiene and prevention of contamination are important layers of protection.
Zoonotic diseases demonstrate why human health cannot always be separated from animal health and environmental change.
A viral disease that can be transmitted from infected animals to people. Prevention depends on animal vaccination, exposure prevention and timely public-health measures.
A bacterial zoonosis associated with infected animals and animal products. It illustrates the connection between veterinary and human health.
Influenza viruses circulating in animals can create opportunities for human infection and require coordinated surveillance.
Tick-borne diseases demonstrate how vectors, wildlife, landscapes, climate and human behaviour interact.
Mosquitoes, ticks and other vectors can transmit infectious agents. Vector-borne disease risk is influenced by ecology, climate, land use, housing and human movement.
Parasites transmitted mainly by infected mosquitoes.
A viral infection transmitted mainly by infected mosquitoes.
A mosquito-borne viral infection associated with birds and mosquito transmission cycles.
A parasitic disease transmitted by infected sand flies.
How might changing temperature, rainfall, ecosystems and human settlement alter where vectors can survive and where people may be exposed?
Infectious disease is much broader than viruses and bacteria. Fungi and parasites cause major illness and can be especially important when immune systems are weakened or when environmental conditions favour transmission.
Fungal infections range from common skin infections to serious invasive diseases. Examples include ringworm, candidiasis and some environmentally acquired fungal infections.
Parasites include organisms such as protozoa and helminths. Their transmission can involve vectors, food, water, soil or direct exposure.
A parasitic disease associated with freshwater exposure in endemic settings.
Parasitic worms associated with contaminated soil and conditions involving sanitation and hygiene.
Vaccination is one of the most important tools for preventing infectious diseases. But vaccination programmes are also complex health-system interventions requiring evidence, supply chains, trained professionals, surveillance, communication and equitable access.
A highly contagious viral infection that can be prevented through vaccination.
A viral disease for which global eradication efforts continue.
A bacterial respiratory infection for which vaccination provides important protection.
Vaccination against HPV is an important cancer-prevention strategy.
Vaccination can prevent hepatitis B infection.
Vaccination protects against tetanus, which is not normally transmitted between people.
Antimicrobial resistance occurs when microorganisms change in ways that make medicines less effective against them. AMR can make infections harder to prevent and treat and threatens modern medicine.
AMR is influenced by antimicrobial use and transmission across human health, animal health, food systems and the environment. It therefore requires coordinated action across sectors.
One Health recognizes that the health of people is closely connected with the health of animals, plants and ecosystems.
Infectious-disease events can range from localized outbreaks to epidemics affecting regions and pandemics affecting populations across countries and continents.
Surveillance and laboratory systems identify unusual disease patterns.
Public-health teams investigate cases, clusters and possible sources of transmission.
Clear, timely and evidence-informed risk communication helps communities make informed decisions.
Health systems coordinate prevention, clinical care, testing, vaccination and other appropriate interventions.
Every outbreak can generate evidence that improves future preparedness.
Preparedness begins before the next outbreak occurs.
A pathogen may be microscopic, but an effective response requires people, institutions, information, infrastructure and leadership.
Detecting and monitoring disease patterns.
Identifying pathogens and supporting diagnosis and surveillance.
Ensuring appropriate access, supply and delivery.
Healthcare and public-health professionals are essential to prevention and response.
Communities need trustworthy, understandable and timely information.
Infectious threats can cross borders, making cooperation essential.
Infectious diseases do not affect all populations equally. Exposure, vulnerability, access to prevention and access to treatment can all be shaped by social and economic conditions.
Poverty, housing, crowding, education, employment, WASH, discrimination, nutrition, environment and healthcare access can influence infectious-disease risk.
Prevent disease and promote health and well-being.
Water, sanitation and hygiene are fundamental to infectious disease prevention.
Health protection should not depend on where someone is born or how much they have.
Environmental change can alter some infectious-disease risks.
Infectious diseases demonstrate one of the central ideas of global health: our health is connected to the health of other people, communities, animals and environments.
Choose the best answer. The goal is understanding, critical thinking and application — not memorization.
Apply what you have learned to global health challenges.
Global health is not only about understanding diseases. It is about asking better questions, identifying inequities, imagining solutions and acting responsibly.
Identify one infectious-disease challenge affecting your school, community, country or another part of the world.
What evidence would you need before proposing a solution?
Who is most affected? What social or environmental factors might explain the difference?
Can technology, data, innovation or collaboration help?
How can I move from learning to thinking, from thinking to innovation, and from innovation to responsible action?
GHE encourages young people to explore primary and authoritative public-health sources rather than relying on social-media claims. Always check the date and context of health information.
Infectious diseases teach us that global health requires knowledge, evidence, critical thinking, innovation, equity and responsible leadership.