By Wynne Parry, Elizabeth Peterson - Live Science
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 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.
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.
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.
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).
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.
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.
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.
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 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.
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 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.
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.
Though rare, Ebola virus disease (EVD) is an often fatal infection caused by one of the five strains of the Ebola virus. The virus spreads very rapidly, overcoming the body's immune response and causing fever, muscle pain, headaches, weakness, diarrhea, vomiting and abdominal pain. Some who contract Ebola also bleed from the nose and mouth in the late stages of the disease — a condition known as hemorrhagic syndrome.
The Ebola virus is spread from person to person through bodily fluids, and a healthy person can contract the virus by coming into contact with an infected person's blood or secretions or by touching surfaces (like clothing or bedding) containing these fluids.
The largest outbreak of Ebola began in West Africa in 2014. When the outbreak ended in 2016, approximately 11,325 people had died in the outbreak, with 28,652 suspected and confirmed cases of the virus reported, according to the CDC. In August 2018, the Democratic Republic of Congo announced an outbreak of Ebola in its northern province of Kivu. That outbreak, which has infected 3,428 people and killed 2,246 as of February 2020, is still ongoing. A vaccination for close contacts of Ebola patients, called rVSV-ZEBOV, was approved in 2019.
Its name is not the only complicated thing about variant Creutzfeldt-Jakob disease, or vCJD. This rare and fatal disease is, as its name implies, a variant of Creutzfeldt-Jakob disease (CJD). It's classified as a Transmissible Spongiform Encephalopathy (TSE) — transmissible because it can be spread from cattle to humans and spongiform because it causes a characteristic "spongy" degeneration of brain tissue.
Humans can get vCJD when they eat beef from cows with Bovine Spongiform Encephalopathy (BSE), a disease similar to vCJD that occurs in cattle. Between 1996 and March 2011, approximately 225 cases of vCJD were reported in the United Kingdom and several other countries. Before 1996, scientists didn't know that people could acquire CJD from eating meat contaminated with BSE. Most people who had the disease prior to then acquired it sporadically or because of a particular gene mutation linked to the disease. And about 5 percent of all reported cases resulted from accidental transmission of the disease via contaminated surgical equipment or certain eye and brain tissue transplants.
Individuals infected with vCJD tend to be younger than those infected with CJD. The median age of people with vCJD is 28, whereas that for CJD patients is 68, according to the WHO. Those with the variant version of the disease tend to exhibit psychiatric symptoms, including depression, apathy or anxiety.
Marburg virus belongs to the Filovirus family of viruses, whose defining characteristic are the filamentous shapes of the viral particles. The disease it causes, Marburg virus disease (MVD), is spread from person to person through bodily fluids, much like Ebola. Marburg virus has other things in common with Ebola, as well. It's transferred to humans by fruit bats belonging to the Pteropodidae family, and it can cause viral hemorrhagic fever in some patients.
Marburg virus was first identified in Germany in 1967 after lab workers who had handled infected monkeys imported from Uganda became sick with the virus, according to the WHO. Monkeys, like humans, can be infected with Marburg virus. Fruit bats, however, aren’t sickened by the Marburg virus (or the Ebola virus); they are simply reservoirs or hosts of the virus.
