Influenza virus
Seasonal flu
A respiratory infection that can cause fever, cough and body aches.
Vaccine available
Seasonal flu ↗Common
Pathogens
Different microbes. A common challenge.
Viruses, bacteria, fungi and parasites are everywhere—in the air we breathe, the food we eat, the water we drink and the people and animals around us. Most microbes are harmless or beneficial, but some cause infections. Understanding major pathogens helps us make informed choices about prevention and health.
Explore the pathogens →VIRUSES Small particles. Big impact.
Explore viral infections →Viruses replicate inside host cells and cause illnesses ranging from mild infections to severe disease.
SARS-CoV-2
COVID-19
A respiratory infection with variable severity, including persistent symptoms in some people.
Vaccine available
COVID-19 ↗Varicella-zoster virus
Chickenpox / Shingles
Causes chickenpox; later reactivation can cause shingles.
Vaccines available
Chickenpox / Shingles ↗Measles virus
Measles
A highly contagious infection that can cause serious complications.
Vaccine available
Measles ↗Mumps virus
Mumps
Often causes painful swelling of the salivary glands.
Vaccine available
Mumps ↗Rubella virus
Rubella
Usually mild, but infection during pregnancy can harm the developing baby.
Vaccine available
Rubella ↗Hepatitis B virus
Hepatitis B
Can cause chronic liver infection, cirrhosis and liver cancer.
Vaccine available
Hepatitis B ↗Human papillomavirus
HPV
Some types cause warts; persistent infection with certain types can lead to cancer.
Vaccine available
HPV ↗BACTERIA Single cells. Diverse diseases.
Explore bacterial infections →Bacteria are living microorganisms. Many are beneficial; some cause infections ranging from mild to life-threatening.
Streptococcus pyogenes
Strep throat
Can also cause skin infections and, less commonly, invasive disease.
No licensed vaccine
Strep throat ↗Streptococcus pneumoniae
Pneumococcal disease
Can cause pneumonia, meningitis and bloodstream infection.
Vaccines available
Pneumococcal disease ↗Staphylococcus aureus
Staph infections
Can cause skin and invasive infections; some strains are antibiotic-resistant.
No licensed vaccine
Staph infections ↗Mycobacterium tuberculosis
Tuberculosis (TB)
Usually affects the lungs, but can involve other organs.
BCG in selected settings
Tuberculosis (TB) ↗Escherichia coli
E. coli infections
Many strains are harmless; others cause intestinal or urinary infections.
No routine human vaccine
E. coli infections ↗Salmonella enterica
Salmonellosis / Typhoid
Different types cause gastroenteritis or typhoid fever.
Typhoid vaccines only
Salmonellosis / Typhoid ↗Neisseria meningitidis
Meningococcal disease
Can cause meningitis and rapidly progressing bloodstream infection.
Vaccines available
Meningococcal disease ↗Helicobacter pylori
H. pylori infection
Chronic stomach infection can contribute to ulcers and stomach cancer.
No licensed vaccine
H. pylori infection ↗FUNGI Often harmless. Sometimes harmful.
Explore fungal infections →Fungi are eukaryotic organisms. Yeasts and molds can cause local or invasive infections.
Candida albicans
Candidiasis
Can cause thrush and other mucosal infections, or invasive disease in vulnerable people.
No licensed human vaccine
Candidiasis ↗Aspergillus spp.
Aspergillosis
Inhaled spores can cause allergic, chronic or invasive lung disease.
No licensed human vaccine
Aspergillosis ↗Cryptococcus neoformans
Cryptococcosis
Can cause lung infection and meningitis, particularly with impaired immunity.
No licensed human vaccine
Cryptococcosis ↗Histoplasma capsulatum
Histoplasmosis
Inhaled environmental spores can cause lung infection and sometimes disseminated disease.
No licensed human vaccine
Histoplasmosis ↗PARASITES Complex life cycles. Global impact.
Explore parasitic infections →Protozoa and helminths live in or on a host and can cause persistent infections, especially in particular regions.
Plasmodium spp.
Malaria
Mosquito-transmitted parasites infect liver cells and red blood cells.
Vaccines for P. falciparum*
Malaria ↗Toxoplasma gondii
Toxoplasmosis
Can cause serious disease during congenital infection or impaired immunity.
No licensed human vaccine
Toxoplasmosis ↗Giardia duodenalis
Giardiasis
An intestinal parasite acquired through ingestion of cysts in contaminated water or food.
No licensed human vaccine
Giardiasis ↗Schistosoma spp.
Schistosomiasis
Larvae in contaminated freshwater penetrate skin; adult worms live in blood vessels.
No licensed human vaccine
Schistosomiasis ↗The same knowledge today
can lead to a healthier tomorrow.
Learn, stay informed and take steps to protect yourself and your community from infectious diseases.
Explore prevention →Selected sources and references
- National Academies, 2010 — How infection works
- CDC — Vaccines by disease
- CDC — Types of fungal diseases
- CDC — Causes of parasitic diseases
*RTS,S and R21 vaccines help prevent P. falciparum malaria in children in endemic settings. Vaccine availability and eligibility vary by country, age and risk. These labels describe prevention options, not individual vaccine recommendations. Illustrations are scientific schematics; colors and relative sizes are not literal.
Artwork illustrates the main mechanisms schematically; molecular sizes, colors and distances are not literal.