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World's deadliest diseases: 7 diseases that impacted human history

Dr. Ajay KohliAug 23, 2024

Throughout history, many notable epidemics and pandemics have ravaged civilizations, threatening human existence. But, thanks to the advances made towards virology, surveillance, drug discovery, and vaccine development, humans persevered and survived. Here’s an overview of some diseases that altered the course of human history and healthcare forever.

Contents

1. Bubonic Plague
2. Spanish flu or Influenza
3. Smallpox
4. Cholera
5. HIV/AIDS
6. Ebola
7. Coronavirus

1. Bubonic Plague

Bubonic Plague is a potentially fatal infectious disease caused by the bacterium, Yersinia pestis. Throughout centuries, the disease has erupted several times in different eras, claiming between ten and millions of lives worldwide. However, the devastation reported in the 14th century, also called "The Black Death, " was one of mankind's worst pandemics that killed more than 25 million people, including a third of Europe's population. This ultimately led to the use of quarantine as the primary public health measure.

Symptoms	Prevention and Treatment
Sudden fever	- Avoid handling live or dead animals
Headache	- Use insect repellents with DEET
Chills	- Minimize exposure to flea-infested areas
Weakness	- Wear protective clothing and gloves
Swollen, painful lymph nodes or buboes	- Keep living areas clean and free of rodents
Lung infections, vomiting of blood, scattered black spots	- Seek prompt medical treatment
	- Administer intensive antibiotic treatment
	- Follow healthcare provider's instructions

Pandemic	When and Where	Number of Deaths
First Plague Pandemic	541–549 AD, Asia, Africa, Europe	15–100 million
Second Plague Pandemic	1346–1353, Europe, Northern Africa	75–200 million
Third Plague Pandemic	1855–1912, Worldwide (mainly China and India)	12–15 million

Lung infections, vomiting of blood, and scattered black spots can also be experienced. Plague kills 30 to 90% of those infected without treatment within 10 days of bite exposure. But with intensive antibiotic treatment, the risk drops to 10%. The best way to prevent the spreading of Bubonic Plague is to avoid handling live or dead animals and use insect repellents containing DEET, among other precautions.

2. Spanish flu or Influenza

Influenza or flu is a contagious respiratory disease caused by variants of Influenza viruses. For more than a century, there have been six major Influenza epidemics. But the 1918 to 1920 flu pandemic, popularly known as "the Great Influenza epidemic" or "the Spanish flu," was the most severe, caused by the H1N1 virus with genes from avian origin. The disease killed about fifty million people, mostly young adults, and infected another 500 million amid World War I. In 2009, a relatively mild flu outbreak killed approximately 3,00,000 people.

Humans are host to several types of Influenza viruses, but pandemics occur only when a new strain is transmitted to humans by other animals, such as pigs, ducks, or chickens. Symptoms of the flu range from mild to severe and usually include:

Influenza Viruses	Transmission Source	Symptoms
Various Types	Other animals (e.g., pigs, ducks, chickens)	Fever, runny nose, sore throat, body ache, headache, coughing, watery red eyes, tiredness

Currently, Influenza isn't preventable by vaccines. So, most controlling efforts are non-pharmaceutical, limited to isolation, quarantine, good personal hygiene, disinfectants, and limiting public gatherings.

Event	Type of Virus	Number of Deaths
1510 influenza pandemic	Unknown	Around 1% of those infected
1557–1559 influenza pandemic (Asia, Africa, Europe, Americas)	Unknown	Unknown
1732–1733 Thirteen Colonies influenza epidemic (North America)	Unknown	Unknown
1847–1848 influenza epidemic (Worldwide)	Unknown	Unknown
1889–90 flu pandemic (Worldwide)	H3N8 or H2N2	1 million
1918–20 influenza pandemic: “Spanish flu” (Worldwide)	H1N1	17–100 million
1957–1958 influenza pandemic: “Asian flu” (Worldwide)	H2N2	1–4 million
Hong Kong flu (Worldwide)	H3N2	1–4 million
1977 Russian flu (Worldwide)	H1N1	700,000
2009 swine flu pandemic (Worldwide)	H1N1/09	151,700–575,400
2015 Indian swine flu outbreak (India)	H1N1	2,035
Typical annual seasonal flu*	Various types	290,000–650,000 per year

3. Smallpox

Smallpox, a contagious viral infection caused by the variola virus, has been one of the most widespread causes of human death for centuries. Variola major and variola minor were the two types of Smallpox virus, with variola major being the severe form. The disease was more common in children, but the risk seemed higher for those who came in contact with an infected person or contaminated objects. People who had Smallpox usually had the following symptoms.

fever
vomiting
skin rashes
fluid-filled bumps

While the first mention of Smallpox dates back to the reign of the great Egyptian Pharaoh Ramses V (1156 BC), the outbreak in 18th-century Europe was the deadliest, killing 30% of those infected, mostly babies. Those who survived had extensive body scars, and about a third were left blind. In the 20th century alone, the disease killed around 300 million people. Smallpox was last naturally endemic in 1977. Since then, the success of vaccination has eradicated disease globally.

Year	Outbreak	Number of Deaths	Percentage of Population
735–737	Japanese smallpox epidemic	2 million	About 1⁄3 of Japanese population
1520	Mexico smallpox epidemic	5–8 million	40% of population
1561	Chile smallpox epidemic	Unknown	20–25% of native population
1707–1709	Iceland smallpox epidemic	18,000+	36% of population
1738–1739	North Carolina smallpox epidemic	7,700–11,700	--
1775–1782	North American smallpox epidemic	11,000+	30% of population
1789–1790	New South Wales smallpox epidemic	Unknown	50–70% of native population
1828–1829	New South Wales smallpox epidemic	19000	--
1837	Great Plains smallpox epidemic	17,000+	--
1862	Pacific Northwest smallpox epidemic	20,000+	--
1870–1875	Europe smallpox epidemic	500000	--
1974	Smallpox epidemic of India	15000	--

4. Cholera

Cholera is an acute intestinal infection caused by the bacterium Vibrio Cholera. The illness is marked byprofuse cramping, vomiting, and watery diarrhoea, leading to rapid dehydration. If left untreated, the symptoms turn so severe that patients usually die within hours. Cholera spreads through contaminated food and water, often causing small outbreaks. However, these outbreaks quickly become a crisis if sanitation systems are disrupted.

In the twenty-first century, the illness continues to affect approximately 2.9 million people per year, resulting in 95,000 deaths worldwide, mostly in low- and middle-income countries due to poverty. The African continent, in particular, has been hit hard, with 40 million people living in Cholera-endemic areas at risk of frequent outbreaks. At the same time, more developed countries such as North America and Europe have had virtually no Cholera for a century due to improved sanitation infrastructure and advances in personal hygiene.

Outbreak	When and Where	Number of Deaths
First cholera pandemic	1817–1824, Asia, Europe	100,000+
Second cholera pandemic	1826–1837, Asia, Europe, North America	100,000+
Third cholera pandemic	1846–1860, Worldwide	1 million+
Fourth cholera pandemic	1863–1875, Middle East	600000
Fifth cholera pandemic	1881–1896, Asia, Africa, Europe, South America	298600
Sixth cholera pandemic	1899–1923, Europe, Asia, Africa	800,000+
Egypt cholera epidemic	1947, Egypt	10277
Seventh cholera pandemic	1961–1975, Worldwide	Unknown
Bangladesh cholera epidemic	1991, Bangladesh	8,410–9,432
Latin America cholera epidemic	1991–1993, Peru, Chile, Bolivia, Ecuador, Colombia, Mexico, El Salvador, Guatemala	8000
Zimbabwean cholera outbreak	2008–2009	4293
Haiti cholera outbreak	2010–2019	10075
Yemen cholera outbreak	2016–2021, Yemen	3,886 (as of 30 November 2019)

5. HIV/AIDS

HIV, or human immunodeficiency virus, which causes acquired immunodeficiency syndrome, or AIDS, remains one of the fatal diseases of the 21st century, killing tens of millions since 1981. There are currently 38.4 million people living with HIV/AIDS worldwide, of which over 7 million come from Sub-Saharan Africa.

For decades the illness had no cure. But with awareness and the advent of antiretroviral treatment, the disease has become more manageable, with global HIV death rates dropping from 2.2 million to 1.6 million between 2005 and 2012.

HIV can be transmitted through unprotected sexual contact, intravenous drug use, infected blood transfusion, shared use of injectors, from mother-to-child transmission during pregnancy, childbirth, and breastfeeding. The virus destroys a type of white blood cell essential to a functioning immune system. But as the virus gradually weakens the immunity, it causes symptoms, making it harder for your body to resist infections and other diseases.

Outbreak	Number of Confirmed Cases	Number of Deaths
HIV/AIDS pandemic, 1981–present (Worldwide)	Unknown	35 million+ (as of 2020)

6. Ebola

Ebola is a rare and fatal disease caused by the Ebola filovirus. There are five types of Ebola virus, four of which are known to cause human disease. The Bat is suspected to be the natural reservoir of the virus. Humans contract the disease through direct contact with vomit, infected body fluids, or contaminated objects such as needles and syringes. Symptoms usually begin between two and 21 days after infection and include:

fever
sore throat
severe headaches
diarrhoea
vomiting
muscle pain and weakness
decreased liver and kidney function
bleeding and bruising (both internally and externally)

Several small outbreaks of Ebola have occurred in Africa since its discovery in 1976, but the incident between 2013 and 2016 was the deadliest. The episode began in Guinea and progressed to Sierra Leone and Liberia. Roughly 28,600 people got infected, and 11,325 died before the virus was contained and declared in 2016.

7. Coronavirus

Initially reported in Wuhan in late 2019, the coronavirus illness is caused by the novel SARS-CoV-2 virus. The disease quickly spread like wildfire, resulting in a pandemic. As of mid-October 2022, approximately 6.5 million people had died from the COVID -19 pandemic.

People contract COVID-19 when they inhale virus-containing droplets/aerosols and tiny airborne particles expelled by infected people while coughing, sneezing, or speaking. Symptoms typically appear two to 14 days after virus exposure, with most people tending to have mild to moderate symptoms such as fever, loss of smell, and tiredness. However, severe symptoms may be seen in those with other health problems such as diabetes, cardiovascular diseases, etc. There is no standard cure for COVID-19, but there are many ways to manage it, including oxygen support, antivirals, and, most importantly, vaccines.

Outbreak	Number of Confirmed Cases	Number of Deaths
COVID-19 pandemic (2019-present)	167 million+ (as of May 2021)	3 million+ (as of May 2021)

Disclaimer: The content on this page is generic and shared only for informational and explanatory purposes. Please consult a doctor before making any health-related decisions.

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