The 10 Most Fatal Viruses and Bacteria

Warning: If you're a bit of a hypochondriac or tend to worry about the likely improbable, do not keep reading! These nasty viruses are old and new; some have been around since 10,000 BC and others hav

Warning: If you're a bit of a hypochondriac or tend to worry about the likely improbable, do not keep reading! These nasty viruses are old and new; some have been around since 10,000 BC and others have been created in the lab in the last few years. Some, we have numbers on: How many died, and over what time span. Others, we can only imagine the repercussions should circumstances “friendly” to the virus arise.

There are many things to consider when pondering the deadliness of any disease, be it viral, bacterial or other: Carcinoid, for instance. In the case of a virus, we must consider such factors as how it is transmitted: human to human is much more serious than animal to human. Airborne is worse than waterborne, as air cannot be restricted or contained, of course. How fast-acting is the virus? If extremely fast-acting, death is all but certain, but there isn’t as much time for transmission, which is a good thing. If very slow-acting, it can keep being passed on and on - but there’s more time to get help and try treatments. Centres for disease control have to monitor and take into consideration all of these complex issues.

The World Health Organization (WHO) pools information on current trends in this area. Their site publishes travel warnings and the WHO is also in charge of keeping tabs on global “crowd control.” That's not the control of people’s movements, but rather the control of how viruses travel: Where they originate, what path they take, and so on. We have a lot more information today than in the past – sometimes it feels like too much, as all that information can cause paranoia and panic. Is it better to be over-informed and safe than under-informed and sorry? The professionals keep tabs of what we need to know, and if you pay enough attention - but don’t start obsessing - you’ll know what you need to.

What are some of the world’s deadliest viruses of days gone by as well as in the present? Read on at your own risk.

10 H7N9 Bird Flu

This particular virus appeared for the first time in China early last year. Like others before it, it seems to have originated there. This virus left the mainland with poultry exports and is responsible for a few deaths to date in Hong Kong. Transmission is through exposure to live birds, usually chickens, which have the virus. It may also be caught in a wet environment where carriers (chickens) have been present. It is not transmittable by air - a good thing, as the death rate among the infected is much higher than in your average flu. For instance, the death rate in the US for the average flu is under 6% of people (and many of these have developed a complication, like pneumonia). Last year, China reported that over a nine-month period a total of 136 people had caught the virus. 45 of those died; that's over 33% of those infected.

9 Ebola


On the world’s radar since 1976, this extremely deadly disease kills 70-90% of those infected depending on the strain. Approximately 1,600 people, all in African countries, have died from Ebola in the last 4 decades. Nearly 80 of those perished in Guinea, West Africa earlier this year. The only reason more people have not died of Ebola is that outbreaks are rare and the virus acts quickly. Once symptoms begin, victims are so weak they cannot travel beyond their small village. If it weren’t for this, who knows how many more deaths would be attributed to this aggressive virus? Symptoms include fever, headaches, weakness, muscle pain, vomiting and diarrhea, internal and external bleeding, and finally the failure of multiple organs.

8 Rabies


While rabies is highly preventable through childhood vaccination or a series of vaccinations immediately upon exposure, once infection sets in the fatality rate is close to 100%. Common carriers include dogs, bats, foxes, raccoons and skunks. Any mammal can host the virus, which attacks the central nervous system, often causing violence and aggression in those affected; it also causes severe pain. Victims of this fatal virus eventually fall into a coma and basically suffocate to death, unable to breathe. There is no cure.

7 Measles


Those who don’t know better think measles is no big deal, that in fact it’s a standard childhood disease marking a badge of honor when you’ve had it. Measles, however, is no laughing matter. Known to have been around since at least 1,000 BC, this virus is highly contagious. Symptoms include a high fever that can last up to a week, red and watery eyes, runny nose and cough, all followed by a severe rash. The cause of death is usually pneumonia, dehydration from excessive diarrhea, or encephalitis. Before 1980 widespread vaccination was not common (a vaccine was developed in the 1960s, and the MMR vaccine in 1971), and an estimated 2.6 million people died worldwide each year. Although vaccines are now widely available, it is still the leading cause of death among children, with 122,000 succumbing in 2012, or 14 deaths every hour.

6 Yellow Fever


The first human baterium ever discovered, this was once called the yellow plague. During the 18th and 19th centuries it was considered one of the most dangerous diseases. A disease transmitted by female mosquitoes, it is found in the tropical regions of Africa and South America, but not Asia. Symptoms can start out looking much like other illnesses: chills, fever, nausea, muscle aches, backaches, headaches and loss of appetite. Once infected there is no real treatment other than treating the symptoms. According to the death rate, about 85% of people recover these days, but historically the survival rate was much lower. In cases where death occurs, symptoms usually improve, but then the fever returns. At that point the patient goes into liver failure and gets jaundiced, with yellow eyes and skin, hence the disease’s name.

5 Modified H5N1 Virus


Dutch researchers had the bright idea to tweak the H5N1 virus, once more feared than at present. In its customary form, it is spread by birds and has not posed as much of a threat to humans as initially thought. However, researchers decided to see what would happen if they made it transmissible by air rather than by bird. The closest testing to gauge possible consequences for humans is done with ferrets, and those poor guys dropped like flies once the virus was airborne. Humans have no immunity to the H5N1, making the risk of this one getting out of the lab a very scary prospect indeed.

4 Smallpox


The images of people with smallpox are so horrible, we decided to go with the vaccine instead. Around since at least 10,000 BC, the virus has been treated by homemade vaccines for thousands of years. Scab was scratched under a person’s skin or was ground into powder and inhaled. Though not always successful, this lowered the death rate; without any form of vaccination it was over 50%. In the late 18th Century Edward Jenner developed the first commonly used inoculation using cow pox. Over time the vaccine changed, but had continued success; stringent observation showed the disease to be globally eradicated by 1979, with the last known case occurring in a British lab in 1978. In 1980 The WHO confirmed eradication. There has not been a case since, though countries including the USA and Russia keep stock of the virus, a source of major concern for some scientists.

3 The Plague


There are various plagues, depending on how the infection manifests; they all result from the pathogen Yersinia pestis. Likely beginning in the drier regions of central Asia, the virus “traveled” the Silk Road via black rats and around the world on merchant ships. A host rat is bitten by a flea, who then carries the virus to humans. Still thought to be the worst pandemic in terms of numbers killed (an estimated 75 to 200 million people died over the course of history), the plague lasted for centuries, with three pandemics between the 4th and 19th centuries. The second, a Black Death, peaked in the 14th century and killed up to 60% of Europe’s entire population. Although more rare today, plague still exists, with occasional outbreaks having occurred in Congo, China, Madagascar and New Mexico, and isolated cases being reported every few years, including in the USA.


The Human Immunodeficiency Virus is the cause: the result is Acquired Immunodeficiency Syndrome. However these days, the result is not as immediate or certain as it used to be, thanks to research, trial and error and a combination of strong pharmaceuticals available on today’s market. HIV is passed on during sex or needle sharing, and occasionally during accidents where two people are cut, for instance, with an exchange of bodily fluids: blood, semen, vaginal fluid and breast milk. There is new hope for a cure as two babies born HIV positive have had their status changed to negative after an initial massive drug cocktail; one adult, an American named Timothy Ray Brown, was cured due to an unrelated bone-marrow transplant in 2007. He is still HIV-free today.

1 Replica 1918 "Spanish Flu" Virus


Recreated in the early 2000s from gene fragments found in the lungs of an Inuit woman frozen in Alaskan permafrost in 1918, this virus was, astonishingly, brought back to life purposefully. Scientists involved even released gene-sequencing information, believing the benefits to outweigh the risks. What are the risks? Biowarfare, for one. Benefits include a wider pool of researchers being able to work on vaccines after studying this influenza virus that killed so many, and which has a structure apparently quite similar to the H5N1 bird flu that has scared so many, though killing less than originally feared. How many did the Spanish flu pandemic kill back in 1918? 50 million.

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The 10 Most Fatal Viruses and Bacteria