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The Top 10 Scariest Illnesses and Diseases of all time

Are you looking to venture beyond the borders of the United States? While exploring new lands and immersing yourself in diverse cultures can be a life-changing experience, it’s essential to be aware of the potential health risks associated with international travel. In this article, we delve into the top 10 scariest illnesses and diseases of all time, many of which still pose a threat to travelers today.

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From the notorious Mad Cow Disease to the dreaded HIV/Aids, these ailments have left a mark on human history and continue to challenge modern medicine. By familiarizing yourself with these illnesses and taking the necessary precautions, you can ensure a safer and more enjoyable journey as you embark on your global adventures.

So buckle up and join us as we explore these terrifying yet fascinating diseases that have shaped our world. After this article, make sure to check out the 14 most common diseases while traveling. 

10. Bovine Spongiform Encephalopathy – Mad Cow Disease

Creutzfeldt-Jakob disease basically causes an infected individual’s brain to become porous (great big holes develop), and the individual begins to exhibit signs of dementia, memory loss, speech problems, loss of balance, loss of motor control, seizures, and finally death. While NVCDJ is not Creutzfeldt-Jakob disease, it does exhibit the same symptoms in both bovines and humans, which lead to the name “Mad Cow Disease”.BSE is a disease that primarily occurs in cattle that basically melts the animal’s brain and spinal cord. The origin of this disease is, at present, unknown; but it was discovered that the BSE epidemic through much of the European cattle population was caused primarily by feeding the remains of dead cows to living cows in the form of meat and bone meal (MBM). This BSE infection then spread to humans who ate the infected beef and caused something that science has termed New Variant Creutzfeldt-Jakob disease (or NVCJD).

Where NVCDJ was found to be present in humans there was a 100% mortality rate, and currently 171 people around the world have died from the disease. Another variant of Creutzfeldt-Jakob disease is quite common in the native population of Papua New Guinea, primarily in societies that are prone to cannibalism. This proves that Creutzfeldt-Jakob disease is easily spread by eating infected animals/people, and that you should always be careful of what you eat.

The thing that is so disturbing about NVCJD is that there is the possibility that it still exists in the worlds cattle population as the condition has an incubation period of 4-5 years, and that infected cattle will usually be slaughtered for consumption prior to displaying any symptoms. In this vein, while the disposal of 4.4 million cows during the height of the infection was a confidence-inspiring move, it makes us wonder if the next burger we eat could ultimately lead us to develop BSE.

Now all the vegetarians reading this are saying to themselves: you know, there is a reason I don’t eat meat and you would be quite right, if it weren’t for the fact that beef is so incredibly tasty.

9. Necrotizing Fasciitis – Flesh-eating bacteria

Despite not being the biggest killer out there Necrotizing Fasciitis is just scary. Imagine this, you’re in an accident and you cut your hand. Now the cut may be severe and require the help of a medical professional, or you may not even notice it, what has happened though is that you are now infected with a bacterium that causes Necrotizing Fasciitis. Depending on how deep the cut is you may not know that this has ever happened, until you start vomiting and the cut starts to weep puss. Your skin might start to change color, and blisters form around the outside of the cut, while inside your tissues are slowly dying as toxins are released by this, now, thriving bacterial colony. Eventually, this colony will grow up your arm and reach your torso where, if you haven’t received medical help, you have a 30% chance of surviving.

If you are grimacing at that idea, don’t worry, we are too. The worst thing about Necrotizing Fasciitis is its ability to spread extremely fast, so fast in fact that even if you do receive medical attention in time, your chances of survival are still extremely low. And if you do survive the infection you will more likely than not be permanently scarred for the rest of your life.

The most common form of treatment for Necrotizing Fasciitis is the use of next-generation antibiotics or, if the infection occurs on your limbs, amputation of the affected body part. The biggest risk of death from Necrotizing Fasciitis actually occurs when the bacterial toxins are released into your blood, resulting in sepsis and ultimately death. At present Necrotizing Fasciitis has a 25% mortality rate for individuals who seek medical attention in a timely manner. Basically, it’s one of those things you hope the doctor never says.

8. Methicillin-resistant Staphylococcus aureus – MRSA

MRSA (pronounced Mursa), is the acronym for Methicillin-resistant Staphylococcus aureus, which is probably why this scourge of the hospital was abbreviated. Back in the 1800’s people were legitimately scared of going to the hospital. It wasn’t because of all the funky smells or sick people, however, but rather because they didn’t want to catch any nasty illnesses. MRSA is the modern-day equivalent of Typhoid and Cholera (two diseases that, due to their penchant for infection spread rapidly in medical facilities) for the hospital community.

MRSA is a mutation of the common Staphylococcus aureus bacterium, except that this mutation is resistant to most modern-day antibiotics including Penicillin, Methicillin and cephalosporins, meaning that once you have it, it’s probably not going away. Discovered in 1961 in the United Kingdom MRSA has become a huge problem for hospital staff around the world. It has become such a big problem in-fact that a 2007 study by the United States Center for Disease Control (CDC) suggests that MRSA infections are responsible for more deaths in the USA every year than AIDS, quite a staggering statistic. At present, there are no definitive numbers on how many people have died from MRSA infections since it was discovered, but the latest figure places the death rates in the USA at around 278,000 in 2005.

Staphylococcus aureus most commonly infects an individual’s nose, and you could actually have a Staphylococcus aureus (we’re going to abbreviate this to SA now) colony in your nose and never know it. One of the only ways to tell if a person has a SA infection is to swab the inside of their nose and run tests on the gold that is found. However, if you do present with a fully developed MRSA infection, expect rashes and puss-filled boils that can spread rapidly and cause flesh-eating pneumonia, which sounds to us like an awesome way to spend a couple of weeks.

In order to treat an MRSA infection, the boils have to be lanced and drained, the patient needs to be isolated and basically, you have to be treated with a whole bunch of really sophisticated, really expensive, antibiotics, which may or may not work. On the plus side, however, maggot therapy (literally getting maggots to feed on the MRSA colony) has been shown to provide a viable, less expensive treatment option. Awesome, we guess, but only if you’re not opposed to the idea of maggots chowing down on your flesh. But hey, at least it proves that someone in the medical community is thinking outside the box.

7. Mononegavirales Filoviridae – Ebola and the Family

We’ve all seen the awesome Dustin Hoffman film “Outbreak”, and when you think about this fun organism, that’s exactly what you should be imagining. In the most layman terms possible, the Ebola family of viruses spreads via bodily fluids (although it has been known to spread through skin or membrane contact), and then hides in its host for between 5-10 days. After this, an infected person will usually spike an extreme fever, become weak, and complain of abdominal pain. The problem with these initial symptoms is that they can be linked to a whole host of tropical diseases, so until the secondary symptoms appear the treatment given to a patient is usually wrong, one of the main reasons for the virus’s high mortality rate.

The secondary symptoms are just plain freaky. Imagine this, you think you have the flu, and you hope that’s the reason that you’re sick, then all of a sudden, diarrhea starts, and instead of feces, it’s all blood. It’s around this time that the vomiting will start, and again, nothing but the red stuff baby! Oh, and on a side note, you may also begin to bleed from your eyes, ears, nose, etc. as well as suffering from what scientists like to refer to as “a million tiny internal cuts” (the main cause of death, due to hemorrhaging). Nice huh?

The hemorrhagic virus family (which includes the Marburg Virus, Zaire Ebolavirus, and Hanta Virus), contains some of the scariest illnesses to ever infest the earth. One of the things making this virus family so incredibly unnerving is the fact that most of the diseases in it have stupidly high mortality rates (90% in the case of Zaire Ebolavirus), and extremely short incubation periods. In fact, it’s only due to the short incubation period that these viruses have been contained, as people are usually too sick to travel. But if Ebola ever got into a major city near you then it’s probably time to have a party and see the world out in style.

Since 1976 more than 1,800 people worldwide have died due to the Ebola virus, and this illness is still hanging around in Uganda, Kenya and the Democratic Republic of Congo. In fact, in 2007 all three of those countries reported outbreaks with a death toll of 157, not much, but considering the disease, pretty scary.

6. Plasmodium falciparum and Plasmodium vivax – Malaria

Planning a fun-filled holiday in an exotic destination? Don’t forget the bug repellant, and even then you’re running a major risk. Malaria is endemic in over 100 countries around the world and is a huge risk for approximately 40% of the population. This disease may not be as high profile or fear-inspiring as, let’s say, hemorrhagic fever or BSE; but according to WHO estimates Malaria causes 300-500 million infection cases every year, of which, 1 million results in the death of the patient. Current statistics show that in any calendar year about 10% of the world’s population will suffer from Malaria, meaning that while it doesn’t have the highest death rates, it is probably the most widespread disease currently in existence.

Malaria is a vector-borne disease, meaning that it is not spread directly from person to person. The illness is instead spread through mosquitoes carrying parasites and infected blood, and as such, it is extremely hard to stop an outbreak once it begins (think the Black Death on a much larger level). If Malaria was any more virulent then the chances are that humanity wouldn’t have made it to the 21st century and that we would have become extinct as soon as the west made it to Africa and Asia.

Despite this, and despite the fact that almost 1 million people die from the disease every year (almost the entire population of Trinidad and Tobago), Malaria is largely forgotten by society as a horrific killer. But just in case, make sure you have your injections before going on holiday.

5. Dengue Fever

Located in the same regions as Malaria, this tropical virus is a relative of West Nile Virus, Viral Encephalitis, and Yellow Fever. However it has one major difference, while most viruses have been eradicated from metropolitan areas, Dengue Fever manages to spread rapidly through urban centers mainly through mosquitoes.

There is a vaccine available for Dengue Fever, and the only medical support that patients receive is targeted at managing the disease symptoms. The symptoms of dengue fever display high temperature, vomiting and bloody diarrhea, low red blood count, and low plasma count, all of which can contribute to the death of the victim.

Dengue fever first came onto the global scene in the 1780’s and immediately proved what an incredibly serious organism it was, causing three simultaneous epidemics in North America, Africa, and Asia. Since then global outbreaks of the Dengue virus have tended to occur every 5 – 6 years, during which time the virus mutates, creating a whole new level of worry for the medical profession.

4. Influenza A Virus Strain H1N1 -The Spanish Flu

We all know that during a flu season you are probably going to get sick. In fact outside of the actual sickness part, many people love the flu season, as it gives them a fairly valid reason to stay at home and play the newest Xbox game all day long. However, if you came down with the flu from March 1918 until June 1920, you had a good chance of dying. The scariest thing about the Spanish Flu (which actually originated in France, Sierra Leone, and the USA), was that young healthy people were more likely to die from the illness than old unhealthy people.

The H1N1 flu strain actually attacked the body’s immune system, and individuals who had stronger immune systems actually gave the virus more ammunition in its war to control their body. It was this effect that ended up killing approximately 50-100 million people worldwide (the combined populations of Italy and South Korea), and creating one of the scariest epidemics of the 20th century.

The thing about the Spanish Flu that has scientists and healthcare professionals literally running for the hills is that it hasn’t died out. If you watch TV, or read the news, at all during the winter holiday season then you’ve probably noticed a lot of fuss being made over the flu and the various vaccines that accompany the flu season. The thing about the flu is that it can rapidly mutate and become a whole other level of scary in the space of about six months, and if that happens then it’s Spanish Flu time all over again.

In case you were wondering, Bird Flu or H5N1, is just the latest attempt by the flu virus to permanently remove us from the planet, and despite its lowly 213 death count (don’t forget that there was a global mortality rate of 62%), has proven that it has what it takes to make the Spanish flu look like the common cold.

3. Yersinia Pestis – The Black Death

First exposed to western civilization in the 6th century AD, The Plague of Justinian, as it was first known, managed to kill 40% of all people living in Constantinople (claiming up to 10,000 lives a day), and a full quarter of the total population of the Eastern Mediterranean. The Plague of Justinian, and a later outbreak of the disease in 588 AD, were responsible for 25 million deaths across Europe, and was one of the first major disease epidemics in human history.

The Black Death, or Bubonic Plague, made a triumphant return to Europe in the 14th century, and hung around until the 1700s growing in strength and virulence every time it made an appearance. After a plague outbreak, it was not unusual for up to 50% of the population in major urban areas to have died, leaving large portions of Europe deserted ghost towns. According to modern estimates, the Plague claimed approximately 137 million lives (slightly more people than the total current population of Nigeria) in its successful 400-year run, and had firmly instated itself as one of the most vicious diseases to ever manifest itself on earth.

In the late 1700s European society began to change and because of that hygiene standards started to improve. People stopped hanging out with rats (the source of the disease) and started washing their hands, loosening the disease’s grip on western civilization. However, this fun-filled bacteria continued to wreak havoc in Asia well into the 20th century causing mortality rates in excess of 75% whenever it struck.

Bubonic plague is characterized by blackened bumpy nodes appearing in the areas of a sufferer’s lymph nodes. It was these nodes that gave rise to the name “The Black Death” as anyone exhibiting these blackened spots was almost certain to die. The bacterium that causes the Plague is spread predominately by the bites of infected fleas that have been living on rats carrying the disease. If you’re concerned about a plague in the modern world, just look for large numbers of dead rats and rodents, as that’s a pretty good sign that it is about to strike.

2. Variola major/Variola minor – Small Pox

This lovely relative of chickenpox and the measles is now extinct (we hope) outside of two WHO reference laboratories, meaning that this virus has been relegated to helping scientific research. However smallpox (not to be confused with the “Great Pox”, Syphilis) was one of the most deadly diseases of all time, and if there ever was another outbreak of this disease the consequences would be disastrous. In fact, Small Pox is single-handedly responsible for annihilating entire societies (see “Pilgrims and Spaniards go to America”), which makes us wonder if all those blankets that we received for Christmas may have had other agendas.

It is estimated that during the 20th century, until 1979 when it was deemed to be completely irradiated, smallpox killed between 300 – 500 million people or the equivalent of the total current population of the United States or European Union. The Small Pox variation, Variola major, had a mortality rate of 30 – 35% and both strains were responsible for killing up to 400,000 Europeans each year during the 18th century, giving this virus the title of “the worst disease ever”.

One of the major problems in controlling the spread of Small Pox is the fact that the disease spreads through the air, and not purely on contact with infected pustules, leading to its ability to rapidly move through a population. However, a large scale vaccination effort in the mid 20th century relegated this disease to the path of the Dodo, and outside of the weaponized versions contained in many military arsenals; most ordinary people don’t have much to fear from Small Pox any more. However, while smallpox may be the only illness that has ever been removed from nature by humanity, it did cause more deaths during its reign as the King of viruses than anything else experienced before Aids. But the fact that it is now extinct means that we can shrug our shoulders and go “meh, who cares”.

1. Acquired immune deficiency syndrome – HIV/Aids

HIV/Aids is the pandemic that is currently affecting every man, woman and child on the planet. Originating in Sub-Saharan Africa during the mid 20th century, Aids has spread to every country on earth and current infection estimates state that approximately 33.2 million people worldwide are living with the virus, and that more than 25 million people have died as a result of infection since 1981 (slightly more people than the current population of Malaysia).

Caused by the Human Immunodeficiency Virus (HIV), Aids is spread via contact with infected bodily fluids (blood to blood, or sexual transmission). The progression from HIV to Aids can take up to 10 years, which is one of the biggest concerns about this disease as individuals infected with the virus may not know that they have it, increasing the risk of the infection spreading. Once the disease has progressed to full-blown Aids, without antiviral therapy, a person’s life expectancy is only about 9 months.

The scariest thing about HIV/Aids, outside of the fact that it is incurable, is that the virus itself doesn’t actually do anything apart from attack and weaken an individual’s immune system. Once your immune system is weakened, however, any infection from any malevolent organism (bacterium or virus) can have a deadly effect. On top of this, HIV uses your own immune system to reproduce, staging a type of stealth warfare inside your body to the point where white blood cells start to attack each other. Once this happens and once the virus has developed into Aids, there is not much that can be done.

Out of all the diseases on this list HIV/Aids probably scares more people, only because it is a real, ever-present threat. But if you practice safe sex, and stop playing with other people’s blood, you should be marginally safer than the rest of the population.


There you have it, our top 10 diseases and illnesses of all time. Check out the 4 most terrifying diseases as well as the article on pneumonia:

A story about pneumonia

4 terrifying diseases you never want to get