It seems like a new virus that's trying to kill us pops up somewhere in the world every other day. While the World Health Organization, the Centers for Disease Control and Prevention, and other health organizations monitor the new coronavirus, officials continue to announce the rapid spread of new COVID-19 infections and deaths around the world.
Despite modern sanitary practices, prevention strategies, and vaccines, there is much to fear from tiny imperialistic pathogens—invisible to all but the most powerful microscopes—that invade our cells to replicate, messing them up like a coke-fueled rock band destroys a hotel room after a concert.
All the hand sanitizer, face masks, and toilet paper in the world can’t save us from some of history’s nastiest viruses and the horrifying diseases they cause in humans. Here are eight of the most dangerous viruses the world has ever seen.
1. Ebola Virus
Its melodic moniker may roll off the tongue, but if you contract the virus, that's not the only thing that will roll out of your body: you will probably have a disturbing amount of blood coming out of your gums, for instance. Four of the five known Ebola viral strains cause Ebola virus disease (EVD), which has killed thousands of people in sub-Saharan African nations since its discovery in 1976.
The deadly virus is named after the Ebola River in the Democratic Republic of the Congo where it was first reported, and is classified as a CDC Biosafety Level 4, a.k.a. BSL-4, making it one of the most dangerous pathogens on the planet. It is thought to spread through contact with bodily secretions of infected people. Depending on the virus strain, EVD has an average mortality rate of 50 percent, with a rapid onset of symptoms that start with a headache and sore throat and progress to major internal and external bleeding and multiple organ failure. There’s no known cure, and the most recent cases were reported this year in the Democratic Republic of the Congo.
2. Marburg Virus
In 1967, a group of lab workers in Marburg and Frankfurt, Germany, and in Belgrade, Serbia, contracted a new type of hemorrhagic fever from some virus-carrying African green monkeys that had been imported for research and development of polio vaccines. The Marburg virus is also BSL-4, and Marburg hemorrhagic fever has a 23 to 90 percent fatality rate. Spread through close human-to-human contact, symptoms start with a headache, fever, and a rash on the torso, and progress to multiple organ failure and massive internal bleeding. There is no cure, and the latest cases were reported in Uganda in 2014. An American tourist who had explored a Ugandan cave full of fruit bats known to be reservoirs of the virus contracted it and survived in 2008.
There are many strains of hantavirus floating around (yep, it’s airborne). Different strains, carried by different rodent species, are known to cause different types of illnesses in humans, most notably hemorrhagic fever with renal syndrome (HFRS)—discovered during the Korean War—and hantavirus pulmonary syndrome (HPS), which emerged with a 1993 outbreak in the southwestern United States. Severe HFRS causes acute kidney failure, while HPS gets you by filling your lungs with fluid (a.k.a. pulmonary edema). HFRS has a mortality rate of 1 to 15 percent, while HPS’s is 38 percent. The U.S. saw its most recent outbreak of hantavirus, of the HPS variety, at Yosemite National Park in late 2012.
4. Lassa Virus
This BSL-4 virus gives us yet another reason to avoid rodents. Lassa is carried by a species of rat in West Africa called Mastomys natalensis. It’s airborne, at least when you’re hanging around the rat's fecal matter. Humans, however, can only spread it through direct contact with bodily secretions. Lassa fever, which has a mortality rate of 1 percent (among hospitalized patients the rate is from 15 to 50 percent), causes about 5000 deaths a year in West Africa, particularly in Sierra Leone and Liberia, and deafness is its most common lasting symptom. It starts with a fever and some retrosternal (behind the chest) pain and can progress to facial swelling, encephalitis, mucosal bleeding, and deafness. Fortunately, researchers and medical professionals have found some success in treating early-stage Lassa fever with an antiviral drug.
5. Rabies Virus
Rabies has a long and storied history dating back to 2300 BCE in records of Babylonians who went mad and died after being bitten by dogs. While this virus itself is a beast, the sickness it causes is now is wholly preventable if treated immediately with a series of vaccinations (sometimes delivered with a terrifyingly huge needle in the abdomen). We have vaccine inventor Louis Pasteur to thank for that.
Exposure to rabies these days, while rare in the U.S., still occurs as it did thousands of years ago—through bites from infected animals. If left untreated after exposure, the virus attacks the central nervous system and death usually results. The symptoms of an advanced infection include delirium, hallucinations, raging, and violent behavior in some cases, which some have argued makes rabies eerily similar to zombification. If rabies ever became airborne, we might actually have to prepare for that zombie apocalypse after all.
6. Smallpox-Causing Variola Virus
The virus that causes smallpox wiped out hundreds of millions of people worldwide over thousands of years. We can’t even blame it on animals either, as the virus is only carried by and contagious for humans. There are several different types of smallpox disease that result from an infection, ranging from mild to fatal, but it is generally marked by a fever, rash, and blistering, oozing pustules that develop on the skin. Fortunately, smallpox was declared eradicated in 1979, as the result of successful worldwide implementation of a vaccine.
7. Dengue Virus
The leading cause of death in the tropics and subtropics is the infection brought on by the dengue virus, which causes a high fever, severe headache, and, in the worst cases, hemorrhaging. The good news is that it's treatable and not contagious. The bad news is there's no vaccine, and you can get it easily from the bite of an infected mosquito—which puts about 3 billion people at risk. The CDC estimates that there are over 400 million cases of dengue infection and that 100 million people suffer symptoms each year. It's a great marketing tool for bug spray.
8. Influenza Virus
No virus can claim credit for more worldwide pandemics and outbreaks than influenza. The Spanish flu in 1918 is generally considered to be one of the worst pandemics in human history, infecting 20 to 40 percent of the world's population and killing 50 million in the span of just two years. The H1N1 swine flu was its most recent newsmaker, when a 2009 pandemic may have caused between 100,000 and 400,000 deaths worldwide in its first year.
Effective influenza vaccines exist, and most people easily survive infections. But the highly infectious respiratory illness is cunning—the virus is constantly mutating and creating new strains. Thousands of strains exist at any given time, many of them harmless, and vaccines available in the U.S. cover only about 40 percent of the strains each year.