Epidemiology

AHL IB Biology

What is epidemiology?

• The study of the spread of disease and the factors that influence its spread

Emerging Infectious Disease

• Mutation of organism to new serovar (antigenic type)

• Migration of humans and animals into new environments

• Travel• War and natural disasters• Decline in vaccination rates• Climatic changes

Microbe of the Day• Vibrio cholerae

• Gram negative curved rod

• Toxin alters sodium pump in intestinal cells fluid loss

• Water-borne bacteria

• High virulence and can kill within hours

London in the 1800s – what

comes to mind when you see

these pictures?

31st August 1854

• Outbreak of cholera in the Soho section of London

• In a single night 56 cases of cholera were reported all within a few block of each other

• Nearly 500 people lost their lives before the outbreak was over

What is wrong with these posters?

The Miasma Theory• People lived in very crowded conditions

• The streets full of sewage and livestock

• 900 people in 2 buildings -180 feet deep x 5 stories – 1 pump a block away, privy in yard

• Germ theory of disease not widely accepted

• People believed that bad smells carried disease

• But one man thought otherwise…..

The father of epidemiology – John Snow

• He noticed people with cholera developed immediate digestive problems-cramps-vomiting-diarrhea

• Face, feet, hands shriveled and turned blue-died in less than a day

• Probably spread by vomiting and diarrhea

• He thought the disease was being spread through a contaminated water source but no one believed him

John Snow uses the Scientific method to prove the skeptics wrong

• Comparison of pump location with cholera deaths-first 3 days of epidemic

The Great Experiment

• Two water companies supplied central London

• Customers mixed in same neighborhood

• Snow went door to door asking which water company served home and compared locations with cholera data

He went door to door questioning everyone who drank from the pump and recording their symptoms…

• Of 83 people infected-only 10 lived closer to a different pump than Broad Street

• Of these 10– 5 preferred taste of

Broad Street water – 3 were children who

went to nearby school

The Great Experiment

• Lambeth Company: -water intake upstream of London-sewage outfall into Thames

• Southwark & Vauxhall Company: -water intake downstream of sewage outfall

The Great ExperimentNo of houses Number of deaths Number of deaths

per 100,000

Southwark and Vauxhall

40,046 1263 315

Lambeth 26,107 98 37

Controlling the spread of infection

• Snow convinced neighborhood council to let him remove handle from water pump on Broad Street - number of new cases declined dramatically

• Many on council still not convinced by his evidence

• Later, people learned that the well below the pump was about 28 feet deep.

• But close by ran a sewer that was only 22 feet below ground level.

• A few days before people got sick, some people remembered a bad smell near the pump.

• The raw sewage had seeped through the ground and into the well.

• As more people got sick, the sewage contained more of the microbes that caused cholera.

• That made the water even more contaminated

Now try the Cholera Outbreak worksheet

Epidemics can lead to pandemics• A large number of people in different

countries all suffering from the same infection

H5N1 BIRD F lU

2003307 DEATHS

SPANISH FLU1918

50-100 MILLION DEATHS

AIDS1981

25 MILLION DEATHS

BUBONIC PLAGUE

134825 MILLION

DEATHS

The Black Death

Yersinia pestis is the bacterium that causes the Black Death plague.

Infected fleas transmit yersinia pestis primarily among rodents.

When a plague outbreak among rodents kills many of them, infected fleas that were feeding on the rodents' blood jump to other animals and humans, carrying the infection with them.

Electron micrograph image

Bubonic plague This is the most common type of plague in humans, accounting for the majority of naturally occurring cases.

Bubonic plague is characterized by an enlarged, infected lymph node called a bubo.

Septicemic PlagueSepticemic plague occurs when plague bacteria multiply in your bloodstream.

You can contract this form of plague when bacteria transmitted by a fleabite enter directly into your bloodstream, or as a complication of bubonic or pneumonic plague.

Pneumonic Plague•You can also develop pneumonic plague as a complication of bubonic or septicemic plague, if the bacteria spread to your lungs.

•Pneumonic plague progresses rapidly and may cause respiratory failure and shock within two days of infection.

Europe Before the Black Death

•By the early 1300’s Europe was experiencing a mini ice age.

•Unusually heavy rains between 1315 and 1319 destroyed grain crops across Europe.

•Many Europeans died or were weakened by famine (widespread starvation).

How will this affect the ability of the population to resist infection?

Origins•Bubonic plague was first seen in China c. 1331

•In 15 years had spread across Asia to the Black Sea.

The Black Death in Europe

Medieval Art indicate the effects of the Plague

Bring out your dead!

An obsession with death.

Boccaccio in The Decameron

Boccaccio in The Decameron

“The victims ate lunch with their friends and

dinner with their ancestors”

The Danse Macabre

Attempts to Stop the Plague

Flagellanti:Self-inflicted “penance” for our

sins!

A Doctor’s Robe

“Leeching”

MEDIEVAL CURES1. The swellings should be softened with figs and cooked onions. The onions should be mixed with yeast and butter. Then open the swellings with a knife.

2. Take a live frog and put its belly on the plague sore. The frog will swell up and burst. Keep doing this with further frogs until they stop bursting. Some people say that a dried toad will do the job better.

Pograms against the Jews

“Jew” hat

“Golden Circle” obligatory badge

Burning Jews

The Consequences of The Black Death

• Have a look at a primary source from the time of the Black Death and try and answer the questions