It seems like a new virus that's trying to kill us pops up somewhere in the world every other day. The World Health Organization recently announced that it is monitoring a new contagious, respiratory-infection-inducing coronavirus (suggested codename: Middle East respiratory syndrome coronavirus or MERS-Cov) that is responsible for dozens of illnesses and several deaths in the Middle East and Europe in the last few months.
While a handful of deaths does not a pandemic make, 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-fuelled rock band destroys a hotel room after a concert.
All the hand-sanitizer in the world can’t save us from some of history’s nastiest viruses and the horrifying diseases they cause in humans - and we know you’re just itching to know all about them. Here are eight of the deadliest viruses the world has ever seen.
1. Ebola
Image credit: Wikimedia Commons/Erin McCarthy
Its melodic moniker may roll off the tongue, but if you contract the Ebola virus (above), that's not the only thing that will roll off one of your body parts (a disturbing amount of blood coming out of your eyes, for instance). Four of the five known Ebola viral strains cause Ebola haemorrhagic fever (EHF), 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 close contact with bodily secretions. EHF has a 50 to 90 percent mortality rate, 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 at the end of 2012 in Uganda.
2. Marburg
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In 1967, a group of lab workers in Germany (Marburg and Frankfurt) and Serbia (then Yugoslavia) contracted a new type of haemorrhagic 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 haemorrhagic 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 trunk, and progress to multiple organ failure and massive internal bleeding. There is no cure, and the latest cases were reported out of Uganda at the end of 2012. 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. (But not before bringing his sick self back to the U.S.)
3. Hantavirus
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There are many strains of hantavirus floating around (yep, it’s airborne) in the wake of rodents that carry the virus. Different strains, carried by different rodent species, are known to cause different types of illnesses in humans, most notably haemorrhagic fever with renal syndrome (HFRS) - first discovered during the Korean War - and hantavirus pulmonary syndrome (HPS), which reared its ugly head 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 (edema). HFRS has a mortality rate of 1 to 15 percent, while HPS 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
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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. It’s airborne…at least when you’re hanging around the rat's faecal matter. Humans, however, can only spread it through direct contact with bodily secretions. Lassa fever, which has a 15 to 20 percent mortality rate, causes about 5000 deaths a year in West Africa, particularly in Sierra Leone and Liberia. It starts with a fever and some retrosternal pain (behind the chest) and can progress to facial swelling, encephalitis, mucosal bleeding and deafness. Fortunately, researchers and medical professionals have found some success in treating Lassa fever with an antiviral drug in the early stages of the disease.
5. Rabies
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Rabies has a long and storied history dating back to 2300 B.C., with 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 and raging, violent behaviour 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
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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 the vaccine.
7. Dengue
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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, haemorrhaging. 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 at least a third of the world's human population at risk. The CDC estimates that there are over 100 million cases of dengue fever each year. It's a great marketing tool for bug spray.
8. Influenza
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No virus can claim credit for more worldwide pandemics and scares than influenza. The outbreak of 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. (A reconstruction of that virus is above.) The swine flu was its most recent newsmaker, when a 2009 pandemic may have seen as many as 89 million people infected worldwide.
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 at large each year.
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