There are four types of pathogens:

• Bacteria – these are microscopic single celled organisms. Many bacteria are harmless but some lead to infections and ill-health such as tuberculosis, salmonella or cholera.
• Viruses – these are extremely small pathogens that contain genetic material such as COVID-19, HIV or hepatitis. Unlike other pathogens they lack the complex structure of a cell and therefore need to enter the cells of other living organisms in order to replicate.
• Fungi – these are a type of organism that includes yeasts, molds and mushrooms. Many are harmless but some cause infections and in humans commonly affect the skin and mucous membranes.
• Protists – these are microscopic single celled organisms. Some protists are parasitic and live on or inside another organism and use the organism’s nutrients to survive. For example, the disease malaria is caused by a bite from a mosquito that has been infected by a parasite.

Despite improved hygiene, vaccination and antimicrobial drugs leading to a considerable reduction in the burden of communicable diseases in the England and Wales, infectious diseases still contributed to over 5,000 deaths in 2019 and by March 2021 COVID-19 had caused or contributed to over 140,000 deaths Office for National Statistics (2021).