Influenza (also called the flu) is a highly contagious disease that attacks the respiratory system and is caused by a number of types of influenza viruses. While it’s possible that there have been influenza outbreaks since 6,000 BC, the first written record of an influenza epidemic, and the respiratory illness we know today, was in 1510.

While there are types of influenza that come from humans, influenza pandemics usually take place when a new strain of the virus is transmitted to humans from another animal species, especially animals that we eat (like pigs, chickens, or ducks).

Symptoms of the flu range from mild to severe and usually include fever, a runny nose, sore throat, muscle pain, headache, coughing, and tiredness.

These are some of the worst influenza pandemics throughout history:

*Not a pandemic, but included for comparison purposes.

This deadly disease is an infection of the small intestine that’s caused by strains of the bacterium Vibrio cholerae, though some types are more severe than others. Usually, its symptoms include vomiting, muscle cramps, severe watery diarrhea leading to dehydration, and ultimately, death.

Cholera has been around for centuries (likely originating in the Indian subcontinent) and has caused seven major pandemics starting in 1817 in the Bengal region of India. People can contract the bacteria through unsafe water that has been contaminated with human waste and the bacteria. Unfortunately, cholera still leads to the deaths of 50,000 to 120,000 people every year.

An outbreak of cholera in 1854 in London led Dr. John Snow to recognize the importance of clean water to public health, and to the study of epidemiology, i.e the study of how infectious diseases spread.

Here are the major cholera outbreaks throughout history:

Luckily, we don’t hear about smallpox these days, as it has been completely eradicated due to vaccination. But once, it was one of the deadliest diseases to humans! It was caused by the Variola virus, and symptoms included fever, vomiting, skin rashes, and blisters.

While we don’t know where it originated from, and it has been around for centuries, the first widespread outbreaks took place in 18th century Europe.

Though people in ancient China and India tried to use some methods to inoculate against smallpox (like by rubbing infected scabs or fluid into scratches made on a healthy patient in the hopes of building immunity!) it was only in 1798 that Edward Jenner developed the first version of what we now call a vaccine.

Smallpox was spread between people or via contaminated objects (killing around 500 million people in just the 20th century alone), and the development of this smallpox vaccine really helped to fight the disease.

These are some of the major smallpox pandemics throughout history:

Also known as typhus fever, this disease is actually a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus, all of which are caused by bacteria spread by lice, fleas, and mites. Its symptoms include fever, headache, and a rash.

While it’s likely that typhus has been around for ages, the first described cases were in 1489 AD. However, there have been many outbreaks throughout history, usually starting in places with poor sanitary conditions and overcrowding. Luckily, it is now rare and can be treated with antibiotics like doxycycline.

Some of the worst outbreaks of typhus were:

First identified in 1981, HIV, which is the virus that causes AIDS (or acquired immunodeficiency syndrome), might have come from African chimpanzees and was transferred to humans in the early 20th century.

It was first detected in the Democratic Republic of the Congo in 1976, and for decades the disease had no cure. But now, new treatments have made HIV a far more manageable chronic health condition. In fact, annual deaths from HIV/AIDS dropped from 2.2 million to 1.6 million globally, and two people have even been cured of HIV as of early 2020!

Dengue is a tropical disease that is caused by the dengue virus, which is spread by mosquitoes – especially the Aedes aegypti species. It causes symptoms like high fever, headache, vomiting, muscle and joint pains, and a skin rash, but in some cases, it leads to severe fever, hemorrhagic bleeding, and death.

Luckily, there is now a vaccine for dengue, as well as antiviral drugs being developed to treat it!

While there might have been cases of dengue fever since the 5th century AD, the earliest report of an epidemic is from 1779 when swept across Southeast Asia, Africa, and North America. Since then, until the end of the 20th century, cases were rare. But they have become more frequent due to ecological disruption.

These are some of the major dengue reports throughout history:

Like dengue, malaria is also a mosquito-borne infectious disease spread by the Anopheles mosquito. It’s caused by the Malaria parasite, and its symptoms include fever, tiredness, vomiting, and headaches and in severe cases, they can also include yellow skin, seizures, coma, or death.

In some cases, if the disease isn’t properly treated, the person can have reoccurring symptoms months or even years later!

Nowadays, there are several medications to prevent malaria, as well as antimalarial medications to treat it. In 2020, a vaccine was even developed, and it can reduce the risk of malaria by about 40%!

Some of the worst outbreaks of malaria were:

COVID-19 is caused by a coronavirus (SARS-CoV-2), and was first reported in Wuhan, the capital of China’s Hubei province, in Dec 2019, and is thought to have originated in animals, likely bats. Since then, it has spread around the world.

Coronaviruses are a large group of viruses that often cause respiratory infections, with symptoms ranging from mild to severe, including fever, tiredness, a dry cough, and a loss of sensation of smell. The virus that causes COVID-19 is mainly transmitted through droplets generated when an infected person coughs, sneezes, or exhales.

While there is no specific treatment for COVID-19, there are many ways to manage it, like oxygen support, antivirals, and most importantly, vaccines!

The Casualties are still counting and the details can be found in the website Worldometer.