In this article we are going to be exploring the 25 deadliest diseases that have changed the world. We will be examining their origins, the impacts that they made, and the lessons that we learned from these catastrophic events. The truth is that infectious diseases have had an impact on society for hundreds of years and have led to the collapse of empires.
1. The Plague of Justinian
The Plague of Justinian, which struck in the 6th century, is considered one of the earliest recorded pandemics. The plague originated in the Byzantine empire and was caused by the Yersinia Pestis bacterium which is the same pathogen that was responsible for the Black Death.
2. The Black Death
The Black Death is one of the deadliest pandemics in history, in the 14th century, it devastated Europe and killed somewhere between 75 to 200 million people. It was also caused by the same bacterium as the plague and it spread through fleas and rats, it brought on fever, chills, and painful buboes.
3. Spanish Flu
The Spanish Flu pandemic of 1919 infected approximately one third of the population and was the cause of about 50 million deaths worldwide. Driven by the H1N1 influenza virus, the outbreak spread rapidly and overwhelmed the healthcare systems.
4. HIV
HIV and Aids emerged in the late 20th Century and caused millions of deaths and reamins serious gloabl health issue. The virus is mainly spread through unprotected sex, shared needles, and from mother to child during childbirth. With around 38 million people living with HIV as of 2021—particularly in sub-Saharan Africa—the epidemic has prompted widespread advocacy for safer sex practices and spurred major advances in treatment and prevention.
5. Cholera
Cholera is a deadly bacterial disease that is responsible for multiple pandemics since the 1800s. It is spread through contaminated food and water and thrives in poor sanitation regions. People with the disease suffer from diarrhea which causes severe dehydration. Fast treatment is essential but the Cholera outbreaks have led to improves in water santation and hygiene globally.
6. Smallpox
Once one of history’s deadliest diseases, smallpox spread through respiratory droplets and contaminated objects, killing about 30% of those infected and often leaving survivors with scars or blindness. A global vacinnation campaign led to forming the World Health Organisation and as a result smallpox was eradicated in 1980 becoming a huge success in public health.
7. Tuberculosis
Tuberculosis, commonly known as TB is an old threat that was caused by Mycobacterium. The bacteria targets the lungs and spreads through airborne droplets. Despite it being curable, it is difficult to control due to the rise of drug-resistant strains and poses a major challenge for global health systems.
8. Malaria
Malaria is an illness that is spread through mosquitos and it continues to affect millions of people in tropical regions. Symptoms include fever chills and other flu like symptoms but without treatments it can become fatal. Efforts to control malaria focus on mosquito prevention, medication, and vaccines.
9. Influenza Pandemics
Influenza has had outbreaks in different times in history in dates such as 1957, 1968 and 2009. It is caused by various stains like H2N2, H3N2, and H1N1. These outbreaks have resulted in a lot of deaths.
10. Measles
Another highly infectious virus, this one spreads in the air and can remain for hours. Symptoms include fever, cough and a rash. Vaccines have reduced global cases but declining vaccination rates have led to resurgences.
11. Ebola
Ebola is a virus that spreads through bodily fluids and has a fatality rate between 50% to 90%. It is considered to be a serious public health threat.
12. Zika Virus
The Zika virus was present in 2015 and spread mainly through mosquito bites and also sexually. It usually causes mild symptoms but can lead to serious complications during pregnancy. Prevention efforts focus on mosquito control and public education.
13. West Nile Virus
First identified in Uganda, West Nile virus became a major health concern in the Americas in the early 2000s. Transmitted by mosquitoes, with birds as the primary host, most people show no symptoms—but some can develop neurological issues. Public education and mosquito monitoring are vital for prevention.
14. Lassa Fever
Endemic to West Africa, Lassa fever is a viral hemorrhagic illness transmitted through contact with rodent waste. Early symptoms like fever and vomiting can escalate to severe bleeding and high mortality rates. Efforts to reduce transmission focus on sanitation improvements and community health education.
15. Nipah Virus
Nipah virus, first recorded in Malaysia in the 1990s, is a deadly zoonotic disease transmitted from animals—particularly bats and pigs—to humans. It causes severe respiratory illness and brain inflammation, with fatality rates sometimes exceeding 70%. Its outbreak potential has raised global public health concerns.
16. Hantavirus
Hantavirus is spread primarily through exposure to rodent droppings or urine and can lead to hantavirus pulmonary syndrome (HPS), a condition that starts with flu-like symptoms and can rapidly progress to respiratory failure. Though more common in rural parts of the Americas, education and rodent control remain key to prevention.
17. Creutzfeldt-Jakob Disease (CJD)
Creutzfeldt-Jakob disease is a fatal brain disorder that is relatively rare but is caused by prions—misfolded proteins that trigger neurodegeneration. It can occur sporadically, be inherited, or result from exposure to infected tissue. Rapid cognitive and motor decline make CJD particularly devastating, and its rarity makes it difficult to study and treat.
18. Severe Acute Respiratory Syndrome (SARS)
SARS emerged in 2002 as a novel coronavirus, spreading through respiratory droplets and contaminated surfaces. There were over 8,000 cases and nearly 800 deaths prompting a strong public health response.
19. Middle East Respiratory Syndrome (MERS)
Identified in 2012, MERS is a coronavirus primarily transmitted from camels to humans. Even though its not easy for spreading from human to human, it does have a high fatality rate at approximately 35%.
20. COVID-19
COVID-19 was spread by people that were asymptomatic. The outbreak led to national lockdowns, wearing masks in shops, shop closures, food shortages, and stockpiling. It introduced the two meter rule which meant that even after the pandemic people have socially distanced themselves from each other. The vaccine came and caused a split of opinion about its safety. It moved communication online and put a lot of pressure on the health care system and the catering industry.
