What is a Pandemic and the History of Pandemics

165-180AD - The Antonine Plague

- Roman Troops returning from Middle East brought back small pox or measles - Disease swept through Rome and contributed to fall or Roman Empire

430 B.C. Plague of Athens

- Typhoid (or small pox) Never identified but typhoid current thinking - Killed 30,000-100,000 people in athens - Athens population reduced by one to two thirds

Spanish Flu (1918-1920 AD)

- Virulent strain of Influenza A - Virus turned healthy immune systems against you - Affected nearly one third of world population - Killed 20-100 million - More deadly than all 20th century wars combined - In just 18 months at least 1/3rd of population was infected - Dense troops led to increased infection

Ebola 2014-16; 2018-2019

- West Africa - Killed more than 11,300 people before it was declared over - 2018-19 outbreak in DRC was complex

Endemic Disease

An infectious disease that has a constant or usual presence within a given geographic area or population group

Infectious Diseases

Causedf by interaction between pathogens, animal hosts, disease vectors, people at risk, and socio-cultural/political and natural environments

Epidemic

Occurrence in a community or region of cases of an illness in excess of normal expectancy

Pandemic phases

Phase 1-3 - Predominantly animal infections Phase 4 - Sustained human transmission Phase 5 - Wide spread human infection Post Peak - % of movement events Post Pandemic - Disease at sustained levels

Case Study - Polio

- Polio Virus - Faecal-oral route - Use to be devastating disease - Very effective vaccine has been developed - Almost 99% decline through widespread vaccination and improved living conditions

Infectious Diseases Examples

- Prions - Viruses - Bacteria - Fungi - Protozoa - Multicellular parasites

Pandemic Futures

- 1960s to 70s assumed infectious diseases burden had passed at least in Global North - Chronic diseases emerging as key 'killer' despite other countries still suffering

Plague of 1519

- Around 25 million living in 'Mexico' when Hernandez Cortes arrived in 1519 - Smallpox epidemic killed 5-8 million of indigenous population following 2 years - Over next century, less than 2 million would survive this and other communicable diseases brought by European explorers - Immunologically naive people - Not been exposed to diseases therefore vulnerable

Micro-organism need the right environment to survive

- Biological - Host (e.g. behaviours, genes...) - Social (living conditions, exposure to animals) - Environmental (temp., rainfall) - Economic (poverty) - Political (social unrest, migration, health system access) Etc.

Black Death (1347-1351AD)

- Bubonic plague - caused by bacterium that circulates among wild rodent - Arrived in Western Europe via merchant ships - Killed 75-200 mill, including 40-60% of Europe's population - Killed half of the world's population

Avian Flu/Bird Flu (H5N1)

- Epizootic circulation of avian H5N1 virus led in 2003, to occasional human 'spill over' - 60% fatality rate - Doesn't spread easily from human to human - Reached Phase 1-3

Pandemic Enablers

- High population densities, trade routes, wars, human mobility

Features of Pandemics

- Infectious Disease - High attack rates - Novel - Severe - Wide geographic distribution - Transmitted person to person - Disease movement from place to place - Minimum population immunity

Why do Epidemics and Pandemics Occur?

- Is 'natural' - another micro-organism is trying to survive - If organism thrives and causes widespread disease it becomes endemic-pandemic

HIV/AIDS 1981-

- More than 35 million people living infected - 32 million people have died from illnesses reacting to AIDS

Infectious Diseases in 21st Century

- Optimism misplaced - HIV - Corona - SARS - Dengue - Malaria - Tuberculosis

Transmission Routes

1. Air droplet - E.g. Tuberculosis, Covid-19 - Inhalation 2. Faecal-Oral - Polio - Ingestion of faecal matter - Through poor water and sanitation 3. Sexual - HIV - Syphillus - Unprotected sex 4. Vector-Borne - Malaria - Dengue - Mosquito bite 5. Blood - HIV - Unsafe injections - Transfusion 6. Mother-child - Hepatitus B - HIV - Childbirth/breast milk

Epidemiological Transitions

1st Transition: Foraging to Food Production (10,000 years ago) - Increase in population density, domestication of animals, sedentary lifestyles, social stratification -> shift in disease ecology and increase infectious diseases 2nd Transition: Rise of NCDs - Decline in infectious diseases - Rise in non-communicable diseases (NCD) 3rd Transition: (Re)emerging infectious diseases - Infectious diseases re-emerging - Antibiotic/antimicrobal resistance increases as well as novel diseases

Pandemic

The spread of infectious disease over a very wide area and usually affects a large portion of the population