Contagious diseases have shaped human history and they remain with us today. As the new coronavirus spreads across mainland China and elsewhere around the globe, such infectious diseases are top of mind for many of us. Here’s a look at some of the worst of these infections, from ebola and dengue to the more recent SARS, the new coronavirus and Zika virus.
The new coronavirus
The 2019 novel coronavirus (2019-nCoV) is a new strain of coronavirus that first appeared in Wuhan, China, in December 2019. Though it was only just discovered, 2019-nCoV has already spread rapidly in China and around the world. As of Feb. 10, 2020, the virus has led to more than 40,000 illnesses and 900 deaths in China, as well as more than 400 illnesses and two deaths outside of mainland China. (The vast majority of cases and deaths have occurred in Hubei Province, where Wuhan is located.)
Coronaviruses are a large family of viruses that cause respiratory illnesses. This family includes the viruses that cause SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome).
Because 2019-nCoV is so new, many unknowns remain about the virus, including exactly how easily it spreads, how deadly it is and whether it will cause a global pandemic. (The World Health Organization has declared the 2019-nCoV outbreak a “public health emergency of international concern,” but has not yet declared it a pandemic.)
Studies suggest 2019-nCoV likely originated in bats, but made it’s “jump” to people through a yet-to-be-identified animal, which acted as a bridge between bats and humans.
Smallpox
Scientists think that smallpox, which causes skin lesions, emerged about 3,000 years ago in India or Egypt, before sweeping across the globe. The Variola virus, which causes smallpox, killed as many as a third of those it infected and left others scarred and blinded, according to the World Health Organization.
A photo taken in 1975 shows the village cemetery in the Bangladesh countryside where smallpox victims were buried. The disease is believed to have killed 46 percent of its victims at a hospital in the Dacca, Bangladesh, ravaging the country for centuries.
In 1980, the WHO declared the disease officially eradicated, after a decade-long vaccination campaign. The last remaining samples of the virus are being held in facilities in the United States and Russia.
Plague
Unlike smallpox, this ancient killer is still with us. Caused by a bacterium carried by fleas, plague has been blamed for decimating societies including 14th-century Europe during the Black Death, when it wiped out roughly a third of the population, including in Basel, Switzerland, depicted in this painting from 1349. The disease comes in three forms, but the best known is bubonic plague, which is marked by buboes, or painfully swollen lymph nodes. Though antibiotics developed in the 1940s can treat the disease, in those who are left untreated, plague can have a fatality rate of 50% to 60%, the WHO said.
Malaria
Although it is preventable and curable, malaria has devastated parts of Africa, where the disease accounts for 20 percent of all childhood deaths, according to the World Health Organization. It is present on other continents as well. A parasite carried by blood-sucking mosquitoes causes the disease, which is first characterized by fever, chills and flu-like symptoms before progressing on to more serious complications. By 1951, the disease was eliminated from the U.S. with the help of the pesticide DDT. A subsequent WHO campaign to eradicate malaria was successful only in some places, and the goal was downgraded to reducing transmission of disease, according to the U.S. Centers for Disease Control and Prevention.
The WHO has distributed so-called long-lasting insecticidal nets in order to reduce bites from malaria-carrying mosquitoes, including in Cambodia (shown in image).
Influenza
A seasonal, respiratory infection, flu is responsible for about 3 million to 5 million cases of severe illness, and about 250,000 to 500,000 deaths a year across the globe, according to the World Health Organization.
Periodically, however, the viral infection becomes much more devastating: A pandemic in 1918 killed about 50 million people worldwide. As became apparent from “swine flu” and “bird flu” scares in recent years, some influenza viruses can jump between species.
Tuberculosis
Potentially fatal, tuberculosis or “TB” is caused by the bacterium Mycobacterium tuberculosis, which usually attacks the lungs and causes the signature bloody coughs. In patients suffering from an advanced stage of TB, you can see the effects in a lung X-ray (shown in image). ,
The bacterium does not make everyone it infects sick, and up to one-third of the world’s population currently carries the bacterium without showing symptoms. And among people infected with TB (but not HIV), 5% to 10% become sick or infectious at some time during their lifetimes.
HIV/AIDS
At the end of 2018, about 37.9 million people were living with a Human Immunodeficiency Virus (HIV) infection worldwide, with 25.7 million of those individuals in Africa. About 770,000 people worldwide died from HIV/AIDS in 2018; 49,000 of those deaths were in the Americas, according to the WHO.
While many of the worst offenders on this disease list have a long-standing relationship with humans, HIV is a recent arrival. HIV’s decimating effect on certain immune system cells was first documented in 1981. By destroying part of the immune system, HIV leaves its victims vulnerable to all sorts of opportunistic diseases. It is believed to have emerged from Simian Immunodeficiency Virus (SIV), which infects apes and monkeys.
Cholera
Cholera causes acute diarrhea that if left untreated can kill within hours. People catch the disease by eating or drinking substances containing the bacterium Vibrio cholerae. The bacteria tend to contaminate food and water through infected feces. Since it can take 12 hours to 5 days to show symptoms, people can unwittingly spread the disease through their feces. Thanks to improved sanitation, cases of cholera have been rare in industrialized nations for the last 100 years, but worldwide it kills between 21,000 and 143,000 individuals every year, the WHO estimates.
During the 19th century, however, cholera spread from its home in India, causing six pandemics that killed millions of people on all continents, according to the World Health Organization. During a cholera epidemic in Peru in 1992, a hospital waiting room (shown in image) was converted to an emergency cholera ward.
More recently, a cholera outbreak in Haiti, which began after that country’s devastating 2010 earthquake, had sickened more than 810000 people and killed nearly 9,000, according to a report published in 2018 in The Journal of Infectious Diseases.
Rabies
No longer a significant threat in the United States, rabies is still a deadly problem in other areas of the world. Rabies causes “tens of thousands” of deaths every year in countries in Africa and Asia, according to the WHO. Approximately two people die yearly in the U.S. from the disease, which is transmitted to humans through the saliva of infected animals, particularly dogs.
The initial symptoms of rabies can be hard to detect in humans, as they mimic that of the flu and include general weakness, discomfort and fever. But as the disease progresses, patients may experience delirium, abnormal behavior, hallucinations and insomnia, according to the Centers for Disease Control and Prevention (CDC). To date, fewer than 10 people who have contracted rabies and started to exhibit symptoms have survived.
However, a rabies vaccine does exist and is usually very effective in both preventing infection with the virus and treating infected individuals before they begin to show symptoms.
Pneumonia
Pneumonia might not conjure up the same dread as diseases like rabies or smallpox, but this lung infection can be deadly, especially for those older than 65 or younger than 5.
The disease can be caused by bacteria, a virus or a combination of both, according to Dr. Amesh Adalja, an infectious-disease specialist and a senior associate at the University of Pittsburgh Medical Center’s Center for Health Security. A person can also get pneumonia from a fungal infection, parasites or reactions to certain medicines, Adalja told Live Science in September 2016.
In 2017, there were 49,157 deaths from pneumonia in the United States, according to the CDC.
Infectious diarrhea
Rotavirus, the most common cause of viral gastroenteritis (inflammation of the stomach and intestines), is a diarrheal disease that can be deadly. In 2013, rotavirus killed 215,000 children under the age of 5 globally, according to the WHO. About 22 percent of those deaths occurred in India alone; and overall most of the deaths occur in children living in low-income countries.
The virus causes dehydration, brought upon by severe, watery diarrhea and vomiting. There are four rotavirus vaccines that are considered highly effective at preventing the disease, the WHO says.
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