Infectious Diseases

Infectious diseases are illnesses caused by germs — bacteria, viruses, fungi, parasites, or prions — that can spread from person to person, animal to person, or through the environment. They range from very common mild illnesses (colds, stomach upsets) to life-threatening diseases (sepsis, meningitis) and globally-significant epidemics (TB, HIV, malaria).

Major categories

• Bacterial — pneumonia, typhoid, tuberculosis, UTIs, food poisoning, STIs
• Viral — common cold, flu, COVID-19, hepatitis, HIV, dengue, chikungunya, HPV
• Fungal — ringworm, candida, pneumocystis (mainly in immunocompromised)
• Parasitic — malaria, giardiasis, worms, scabies, lice
• Prion — rare, include Creutzfeldt-Jakob disease

How they spread

• Airborne — coughs, sneezes, droplets
• Contact — skin-to-skin, wound exposure, sexual contact
• Contaminated food or water
• Insect and animal bites
• Mother-to-child (during pregnancy, birth, or breastfeeding)
• Blood and bodily fluids
• Surfaces (fomites)

Common symptoms

Signs vary by disease but often include:

• Fever
• Chills, sweating
• Tiredness, malaise
• Muscle aches, headache
• Cough, runny nose, sore throat
• Nausea, vomiting, diarrhoea
• Rash
• Swollen glands

When to see a doctor urgently

• Very high fever, or fever lasting more than a few days
• Breathlessness
• Stiff neck, severe headache, confusion
• Rash that is new and spreading
• Signs of dehydration (reduced urine, dry mouth, dizziness)
• Persistent vomiting or diarrhoea
• Any infection in a baby, older adult, pregnant woman, or person with weakened immunity

Prevention

• Vaccinations — for many preventable infections (see our Vaccines page)
• Hand washing with soap
• Safe food handling — wash hands, wash produce, cook meat fully, avoid contaminated water
• Mosquito control — drain standing water, use nets and repellents
• Safe sexual practices, condom use
• Don't share needles
• Respect isolation / quarantine guidance during outbreaks
• Manage chronic conditions well — diabetes and weak immunity dramatically increase infection risk
• Early diagnosis and treatment reduces spread