1.3 Diseases in Human History

1.3.1 Bubonic plague

The bubonic plague (i.e., “plague”) is caused by the bacterium Yersinia pestis - it is spread by flea bites, direct physical contact, and the fecal-oral transmission route:

Figure 1.11: Buboe Formation and Tissue Necrosis in Plague Patients

Symptoms of the plague included the following:

1. Fever
2. Weakness and headache
3. Buboe formation (see above)
4. Breathlessness
5. Cough
6. Chest pain
7. Tissue necrosis

The plague is notorious for lethal outbreaks; some of the deadliest are:

1. Byzantine empire (AD 541 - 542)

   25 - 50 million dead (i.e., half of Europe’s population)

2. 14^th century

   25 million Chinese (and other Asians) were dead before the bacterium spread to Europe and peaked (in infections) from 1347 to 1351. The plague haunted Europeans and Mediterraneans throughout the 14^th to the 17^th century, killing 75 to 200 million people in the process!

3. Third plague pandemic in China (1855 - 1859)

   The outbreak started in China and spread to surrounding countries and killed almost 10 million in India alone.

1.3.1.1 Social and economic effects of the plague

The plague was used as a biological weapons in wars (i.e., ancient China, medieval Europe, and by Japan in China).

The plague also lead to the downfall of some cities like Florence in Italy.

There was also renewed fanaticism and religious ferver; other religious, social, and economic upheavals like the “Hundred Years’ War” between the English and the French.

During the Golden age of the 15^th century, land was plentiful, job wages were high, and life was better for farmers!

1.3.1.2 Current status of the plague

Today, there is a vaccination for the plague (though an oral-based vaccine is still being developed).

The treatment of choice for the disease is still a combination of antibiotics (though the bacterium is capable of developing drug resistance); there is still 600 cases per year.

Yersinia pestis remains a potential Biological weapon by bio-terrorists.

1.3.2 Smallpox

This is a disease that is caused by viruses like Variola major or Variola minor. Symptoms of smallpox included the following:

1. Fever
2. Vomiting
3. Sores in the mouth and skin rash
4. Fluid-filled bumps with an indentation in the center

Figure 1.12: Photo of a Child with Smallpox

The disease was spread from human-to-human or via contaminated objects; it had a 30% death rate.

Some notable outbreaks included the following:

1. 18^th century Europe

   An annual death toll of 400000 was recorded; a third of the total cases resulted in blindness.

2. 20^th century

   300 to 500 million people died.

While smallpox has been officially declared as eradicated by the WHO in 1980, it is also the first disease for which a vaccine was developed.

1.3.2.1 Social and economic impacts of smallpox

During the 16^th century, the disease devastated the native Amerindian population (an important factor for South American countries’ conquests by the Spanish).

Smallpox outbreaks had a high mortality rate among native Americans; 90% of native Americans were killed - this aided the settlement of the east coast of the USA.

The disease was also the main cause of death in aboriginal populations between 1780 and 1870 in Australia.

1.3.3 Cholera

Cholera outbreaks in India caused unrest, social conflicts, and fuelled the development of the healthcare system and municipal reform.

Cholera can be treated primary using hydration and antibiotics. The current vaccine for cholera only protects half of those who receive it and only lasts a few months. There is still a need for a better vaccine (a plant based vaccine is still underway).

Cholera can also be prevented with better hygiene practices; drinking boiled or disinfected water, washing one’s hands and face, washing dishes and utensils prior to use, and washing produce prior to eating are good examples.

1.3.4 Yellow fever (i.e., American plaque)

This disease originated in Africa and is caused by the yellow fever virus (an RNA virus) - the virus is transmitted by the Aedes aegypti mosquito:

Figure 1.13: Aedes aegypti Specimens

Symptoms of the disease included:

1. Fever
2. Chills
3. Loss of appetite
4. Nausea
5. Headache
6. Jaundice
7. Bleeding
8. Kidney failure

Some notable outbreaks are:

1. 17^th century

   This happened in the Americas, Africa, and Europe

2. Among French soldiers

   The high amount of French casualties (because of the disease) forced Napoleon to give up his plans for South and North America and sell Louisiana to the US.

3. Philadelphia, 1973

   This drove the government away.

4. Africa, 2013

   There were 123000 infections and 45000 deaths, 90% of which were in Africa.

There are safe and effective treatments for yellow fever; some countries require travelers to be vaccinated against yellow fever prior to entering.

1.3.5 Spanish flu

The H1N1 virus (called “Spanish” flu because of the media - Spain was the only country to openly talk about the disease) infected about 40% of the world’s population within 18 months and killed 20 - 50 million people in total. The virus was thought to have been trasmitted over from a pig to a human and it was very contagious and deadly (it could kill in as fast as 12 hours).

There are three waves of spanish flu outbreaks to be wary of:

1. First wave

   The outbreak began on a military installation in Kansas on March 11, 1918. When the US army deployed to Europe, the virus spread to France and other European countries; fortunately, cases dropped off in the summer of 1918.

2. Second wave

   In late August 2018, the US army bought a deadlier variant of the virus from the UK to France, USA, and Africa. US soldiers were major spreaders of the disease - in September to November of 1918, the death rate skyrocketed.

3. Third wave

   This started in Australia in January 1919; the virus went to Europe and ultimately, the US.

As it turns out, the disease shared a “w” curve: mortality rates were high for the young and the old, but there was also a spike in mortality rates in 25 to 35 year olds. While initially unknown, the cause of the aforementioned was later found to be associated with a “cytokine explosion”: a dangerous immune over-reaction in healthy individuals.

1.3.6 Case study: SARS outbreak in 2002 to 2004

Severe Acute Respiratory Syndrome is a disease caused by a new virus.

1.3.6.1 Important events

On November 16, 2002, China notified the WHO of 305 cases and 5 deaths from a new disease.

On February 2003, SARS arrived in Hong Kong via a patient who was intending to visit his family - he stayed in a hotel and was later hospitalized.

The same virus was then carried to Vietnam, Canada, Taiwan, UK, and Singapore by those who stayed in the same hotel. Consequently, the WHO issued a global alert / emergency travel advisory.

Many healthcare workers were infected; some workers died, including Alex Chao (a doctor in Singapore) and Carlo Urbani (a WHO infectious disease specialist).

1.3.6.2 SARS in Singapore

The first case was a young woman who returned from Hong Kong - she set off a series of transmissions that ended up spreading the virus to 238 people, 33 of whom died.

Compulsory home quarantine was issued for those who were possibly affected. A blanket screening of incoming travelers and school closure was also carried out.

In 2003, Singapore was removed from the WHO’s “infected areas”.

1.3.6.3 SARS virus

Figure 1.14: Electron Micrograph of SARS Virus

The SARS virus is a coronavirus that likely originated from bats and thereafter carried by animals like civet cat and spread to humans.

SARS causes severe illness characterized by muscle pain, headache and fever, cough dyspnea and pneumonia, and decreased lymphocyte counts in the blood.

SARS had a mortality rate of about 9% overall - it was 50% for those 50 years and above.

1.3.6.4 Impact of 2002 - 2004 SARS outbreak

The public’s trust in the government and international organizations were tested. Old practices of disease control was found to be inadequate for SARS.

SARS ended up slowing down many countries’ economies including Singapore’s (low visitor arrival, falling stock prices, poor businesses in restaurants and hotels, etc).

Many countries were also aware of the new dangers that can be quickly spread from other countries to countries of the world.