Lecture 23: The History of Epidemics (Abi Kerr)

Epidemic

Outbreak of a disease (usually infectious but sometimes other conditions) which affects a large number of individuals at the same time. There is a higher than normal incidence within one area or population.

Endemic

A disease that is always present in an area. It has a constant presence with low to no spread.

Pandemic

A global outbreak spreading across continents or countries

How do outbreaks of disease occur

Changes to our interaction with the environment:

• Exploration

• Changes in trade patterns

• Globalisation

• Warfare

• Famine

• Poverty, overcrowding, poor living conditions

• Deforestation

Are pandemics more contagious or infectious

Contagious

What 2 things cause pandemics

Viruses and bacteria

How do diseases spread from human to human

They don’t need an intermediate host

What is Zoonosis

When diseases pass from animal host to human population

Why are pathogens from primates not as dangerous as pathogens from non human related organisms

Primates are like humans therefore we are more likely to become infected however pathogens from non related species may cause a dangerous mutation to occur in order to allow the virus to survive in the human host

Example of organism which could cause potentially dangerous infections to human

Bats

What is one of the main drivers of new diseases

Zoonotic infection

How many human infections have an animal origin

60%

What is a vector

An organism which can pass on an infection (e.g. a mosquito passes on malaria)

What is cholera

Water bourne bacteria

Where does tuberculosis come from

Soil

What human-animal interactions cause infection

• Intensive wildlife farming

• Wildlife hunting

• Live animal markets

• Domesticated animals

• Exotic pet trade

Ways which zoonotic infections are transmitted

• Food

• Water

• Vectors

• Proximity or indirect contact with animal

• Direct contact with animal

Other routes of emergence of disease outbreaks

• Appear from nowhere

• Reemerge after a period of absence

• Disseminate from an isolated population to native population

• Mutation and adaptation

• Natural disasters

Bacteria caused pandemics

• Plague

• Sphilis

• Typus

• Typhoid

• Cholera

How is plague transmitted

Via fleas on rodents

Yersinis pestis: bacteria

How is sphilis transmitted

Sex

Treponema Pallidum

How is Typus transmitted

Contact with fleas

Rickettsia typhi

How is typhoid transmitted

Contaminated food or drink

Salmonella typhi

How is cholera transmitted

Contaminated water

Vibrio cholerae

Virus causing pandemics

• Smallpox

• Influenza

• Polio

• HIV

• Ebola

How is smallpox transmitted

Airborne water droplets

Variola virus

Transmission of flu

Airborne water droplets

Influenza A,B,C,D

How is polio transmitted

Person person contact

Poliovirus

Transmission of HIV

Body fluid

Human immunodeficiency virus

Transmission of polio

Body fluid

Poliovirus

Transmission of Ebola

Body fluids

Ebola virus

what do we have to do to control pandemics

Understand transmission

Order of most deaths by pandemic

1. Black Death (plague)

2. Smallpox

3. Spanish flu

4. Plague of Justinian

5. HIV

6. Plague 3

7. Covid 19

8. Cholera

9. Ebola

10. SARS