I first read about this in a contagion book and it kept me up at night for quite a bit. Interesting personal note, it was that book that first triggered my dedication to prepping.
In 1967, a group of lab workers in Germany (Marburg and Frankfurt) and Serbia (then Yugoslavia) 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 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.)

Wikimedia Commons/Erin McCarthyThere 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 hemorrhagic 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.

Wikimedia Commons/Erin McCarthyThis BSL-4 virus gives us yet another reason to avoid rodents. 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 fecal 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.

Wikimedia Commons/Erin McCarthy 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 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.

Wikimedia Commons/Erin McCarthyThe 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.

Wikimedia Commons/Erin McCarthyThe 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 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.

Wikimedia Commons/Erin McCarthyNo 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.

Also known as Hansen’s disease, is caused by Mycobacterium Leprae, a germ that acts to affect the peripheral nerves, rendering them useless. Without use of such vital nerves, patients often neglect to feel pain and temperature in certain parts of the boy- usually leading to injury and the spread of opportunistic infection. Accounts of the disease date back several millennia, with a great stigma arising around it due to the myth that it causes the loss of limbs- a concept far more terrifying in days gone by. Leprosy is most contagious when allowed to develop in areas of poor hygiene and sanitation.

A mosquito borne disease, has the ability to infect human beings without any warning or restraint whatsoever. Characterized most typically by severe fever and headaches, the condition can often lead to coma’s and even death. Most common in tropical and subtropical climates, malaria parasites arise from the genus Plasmodium and can vary in seriousness depending on the case itself as well as the medical resources available.

Also known as ‘beaver fever’ is an internal parasitic infection caused by the ingestion or exposure to infected volumes of water. As one of the most common waterborne diseases in America, it is expected that the infection is zoonotic- with the belief that beavers (among other animals) may be responsible for the spread of the infection into lakes, rivers and reservoirs- hence the pseudonym.

As the condition which inescapably leads to AIDS, HIV or the Human immunodeficiency virus to give it its full title is the most recent epidemic to strike at our species. Believed to have emerged in Africa in the late 19th Century, the condition leads to the deterioration of the immune system- leaving sufferers extremely vulnerable and at the whim of opportunistic infections, ranging from the most deadly of tumors to the most common of colds. Elevated to the status of pandemic as of 2009, HIV/Aids effects an estimated 33 million people in the world today, with an annual death toll of around 1.8 million. The virus is transmitted through direct contact of a mucous membrane of the bloodstream with a bodily fluid already hosting it- most commonly through unprotected sex and the use of contaminated paraphernalia among drug addicts.

Dermatophytosis, or ringworm as its most commonly known- is a condition brought on by a fungal infection of the skin. A common misconception in relation to the illness is that its symptoms are caused by a breed of parasitic worm, when in fact they are completely the result of several species of fungi. Though far from deadly if taken care of properly, ringworm’s ability to spread from person to person is unrivaled due to the fact it must only come into contact with the skin and not the internal organs/cells.

As a Zoonotic illness, is spread from animals to humans- perhaps the reason for its undisputed notoriety in the middle-ages. Several epidemics of the infection have occurred throughout the world over the course of history, most notably in Europe- where it decimated an estimated half of the continents population during the 14th Century. Spread by flea infested rats, the disease infects the lymphatic system- attacking the immune system directly and causing death as quick as four days after the emergence of initial symptoms.

Though not the most deadly ailment on this list, with a fatality rate of around 20 per cent- is nonetheless a vicious and sly manifestation. With symptoms that possess the ability to lie dormant for a staggering period of time after infection, the Fevers ability to spread unknowingly from person to person is uber-viral. Due to its method of transmission via ingestion of food and water contaminated with feces of those infected, Typhoid Fever is also at its most effective in conditions of bad sanitation.

Though not thought of as a big deal today, or ‘flu’ has a long history of killing human beings. Highly contagious in most forms, the flu attacks the respiratory system causing fever, fatigue, coughing, congested sinuses, nausea, vomiting, diarrhea and aching muscles. An estimated 36,000 people die a result of the flu in the US every year and it spreads primarily through contact, coughing and sneezing- often able to pass on up to one week before symptoms even develop.

This year's big foodborne threat is killer tomatoes. Two years ago, spinach up and vanished from grocery store shelves around the country. Michael Pollan will be the first to tell you why: 'Eighty percent of America's beef is slaughtered by four companies, 75 percent of the precut salads are processed by two and 30 percent of the milk by just one company.' The consolidation of the industrial food supply necessarily means that any pathogen which enters the system will have no trouble finding its way to your dinner plate, heedless of global distances.Compounding that problem, we have the issue of antibiotics being administered as a preventative measure in livestock and poultry. Animals are routinely fed these medicines as part of their diet, whether they are sick or not. This indiscriminate use has undoubtedly led to a reduced efficacy of antibiotics in humans. Dr. Arjun Srinivasan, a medical epidemiologist with the CDC, notes that we don't know whether overuse of antibiotics in humans is ultimately worse than overuse in animals, but that 'there are those who say, if you look at the absolute amount of antibiotics that are used in animals, [it] vastly outweighs the amount that's used in humans. So therefore, that may actually be a larger component' of the problem.

The first of two agents on our list spread by the Aedes mosquito, the yellow fever virus wasn't been much of a concern in the latter half of the twentieth century. Malaria control efforts in the 1950s successfully decimated the Aedes population, and with it the occurrence of yellow fever. In the past few decades, however, the mosquito has returned and is ranging much further than previous generations. It's also making its way into urban environments, which it has done in the past—an outbreak nearly wiped Memphis off the map in 1878—but in recent memory, it has been confined to the tropical jungles.The fever gets its name from the jaundice it can cause after a few days of infection. Later comes internal bleeding (it's a hemorrhagic fever like Ebola and Marburg) followed by bloody vomit with the consistency of coffee grounds. What is most worrying about its return to cities is that it achieves a higher mortality rate among dense, unexposed populations—up to 30 percent. Recent outbreaks in Paraguay and the Ivory Coast have health officials racing to vaccinate as quickly as possible. While an effective vaccine exists, there is no treatment and no cure. CDC

Shanghai SARS Alert Nobody used to pay much mind to the coronaviruses. While the genus is home to two species responsible for the common cold, they haven't received the attention given to other cold-causing viruses because coronaviruses are difficult to grow in a lab environment. That all changed very quickly in 2003 when a new respiratory disease began killing doctors and nurses and showing the potential to spread at pandemic levels was identified as a previously unknown coronavirus. The infection was severe acute respiratory syndrome, or SARS, and it held the world's attention for just under a year before it disappeared in the summer of 2003.The global public health response was a near-unparalleled success. Within weeks, control efforts led by the World Health Organization had identified a totally novel agent, devised a diagnostic test, and instituted plans for quarantine and isolation. It is undoubtedly a result of those efforts that the outbreak was contained before it could reach pandemic levels.And while it is no longer topping watch lists, two questions persist: how did it get to humans and where did it come from? As Dr. Scott Dowell, head of the CDC's Global Disease Detection Program explains, 'how it is that one of these animal pathogens acquires the ability to spread efficiently among humans is something that we don't do a very good job explaining or predicting.'Coronaviruses are known to mutate rapidly, so there may have been some biological basis to its sudden appearance and virulence, but it was still very much a surprise. Where it currently lies in wait is even more of an unknown. There is evidence the 2003 outbreak originated in a wildlife market in southern China, but the exact species of animal from which it came is still very much in contention. DearTerisa (CC Licensed)

This hemorrhagic fever has gained a special notoriety for being a quick and exceptionally deadly killer. Ebola is known as the fever that kills with a million cuts, because it causes a reaction in the blood that produces microscopic holes in the capillary walls. The patient then bleeds to death internally. Mortality can be as high as 90 percent. It is invariably a headline-grabber when outbreaks strike. But it's not on this list because it's presently a significant threat (it's not). It's here for two reasons.The first has to do with a trait Ebola shares with the SARS coronavirus—its zoonotic host is a mystery. Although the virus has been known to us since the mid-1970s, we are still largely in the dark about what its reservoir is in nature. Even after a comprehensive study of tens of thousands of animals in outbreak regions, no virus was found. That points to the difficulty public health officials face when unknown threats emerge—we have a very hard time tracking some viruses we've known about for decades, so you can imagine the mounting complications when starting from zero.The second reason it's on this list is to place it within the context of the rest of the agents. While it is a ravaging disease, it presents little threat outside of where it appears locally. It is not communicable through the air, and only spreads from person to person; often because of poor hospital conditions in the areas in which it appears. In addition, it presents symptoms very quickly—infected persons are likely to be isolated before getting very far. All the rest of the diseases on this list can spread far and wide, which makes them much more threatening. CDC

Methicillin-resistant Staphylococcus aureus,—or MRSA,—is a mutant variant of the common staph infection found in hospitals and nursing homes. What sets it apart from common staph is its resistance to a wide range of commonly used antibiotics. In the late 1990s, it began to appear in people who hadn't been anywhere near a health-care institution. They were struck with what scientists have taken to calling Community-Associated MRSA. The disease appears in places where daily, close contact is the norm: schools, day-care centers, and prisons, for example. If caught early, before it gets into the bloodstream, it is usually treatable with low-grade antibiotics, and its spread can be controlled. It may even be remedied without antibiotics by draining the lesions it raises on the skin. Once it passes that early stage, however, it can become a much more difficult infection to eradicate.MRSA is an important warning sign because doctors are frequently having to use the strongest antibiotics to treat it. We know this to be an effect of antibiotic overuse. The end result is a breed of bacteria against which we have little, if any recourse for a cure. 'The challenge that we'll face is that a growing number of bacterial infections will be more and more difficult to treat. The reports are rare, but we're already seeing [cases] of bacteria... where there are no effective antibiotics to treat the infection,' says Dr. Srinivasan. Right now, these cases are appearing only in hospitals and only in the most immunocompromised patients, but that was once the case for drug-resistant staph, too.The only real, immediate course of action is education and vigilance about proper antibiotic use, because, as Dr. Srinivasan notes, 'our ability to develop new drugs has already been surpassed by the speed with which bacteria are developing resistance.' Several institutions have undertaken awareness campaigns, like the CDC's 'Get Smart' program and the Infectious Diseases Society of America's 'Bad Bugs, No Drugs,' both of which have had good success educating both patients and health-care workers. CDC

Enterovirus 71 Hand, foot and mouth disease is a pretty common childhood illness caused by a variety of viruses generally considered to be benign. Infected kids get a mild fever and spots around their mouths; the whole thing lasts a few weeks. No big deal -- until one of the strains, enterovirus 71, decides to ratchet things up substantially and become highly lethal. Cases of sudden death from EV71 in children have been steadily increasing in Asia since the late 1990s. The most recent outbreak, which began in early May in southern China, has already claimed the lives of nearly 40 children under the age of six, with the number of reported infections climbing into the tens of thousands.It's unclear just how the fatal strain of EV71 manages to kill, but the evidence so far seems to indicate that it travels into the brain stem of a child and from there shuts down the respiratory system. Like many of the viruses on this list, no treatment or vaccine exists. What's worse, there is no reason to think it won't make its way to the U.S. And, as Dr. Dowell explains, 'if it does come to the U.S., there's no real reason to think that we would do any better with it than the Chinese in Anhui providence have.' MidgleyDJ (GNU Licensed)

All that stands between us and an influenza pandemic on a scale that could dwarf the Spanish Flu of 1918 is a handful of genetic mutations in a virus known to have a high mutation rate. Presently, the influenza variant known as H5N1—commonly called the avian flu—can only readily move from an infected bird to a human. We have been lucky to limit its spread to no further than any one single family cluster, but that is largely due to the fact that it has yet to acquire the ability to move effectively from human to human. It could simply be a matter of the virus having yet to land in someone already infected with another strain of influenza for H5N1 to pick up the genetic material necessary to make the leap.To give you a little historical perspective of where we may be headed, consider the influenza pandemic of 1918. The overall mortality rate of that flu was considerably higher than the normal annual rate of flu infections, topping out around 2 percent. The H5N1 variant has shown itself to have a mortality rate in the neighborhood of 60%. According to Dr. Dowell, 'if there are a few mutations in that virus and it acquires the ability to spread efficiently from person to person, it's hard to imagine historically anything to compare it with.' Cynthia Goldsmith

Personal Note from the curator : I test positive (PPD) for this one. ...luckily I have not become active.

Tuberculosis was once called consumption, because of the way it would overtake a person's being, appearing to consume them from within. Infection causes the victim's eyes to redden and swell, and skin slowly to go pale; the incessant coughing eventually brings up blood. It is an old disease. Its effects have been seen in the bones of prehistoric man. It has managed to insinuate itself in the human population so thoroughly that the World Health Organization estimates one out of every three people on Earth has been exposed to it.For a disease with which we have had such a long and intimate relationship, one would hope we'd have a pretty good handle on things by now. While we have for many years been adeptly developing antibiotics to fight TB, the tuberculosis bacterium has in many ways been more adept at surviving them. Of particular concern are the strains of TB classified as multiple-drug-resistant (MDR-TB); at the top of that list is XDR-TB, or extensively-drug-resistant tuberculosis.XDR-TB is of great concern because it is now resistant to not only the first- and second-line antibiotic agents, but one of the third line as well. The strain is making us reach deep within our well of defenses, and the current concern is that it will soon outpace the remainder of the third line. It has a much higher mortality rate than even MDR-TB, and can be a terribly severe infection. Fortunately, the trade-off for all its virulence is that it does not spread easily among healthy populations, which may be why it is not as widespread as we might expect. Among those with already compromised immune systems, however, it is capable of reaching epidemic proportions. CDC

Within hours of contracting cholera, it is possible to die. The bacteria attach to the wall of the small intestine and immediately begin producing toxic proteins that induce severe, unrelenting diarrhea. Without a very simple remedy of salt and sugar water, a person can dehydrate to the point of dangerously low blood pressure, followed by shock and heart failure.Fortunately, it is relatively easy to control. With proper sanitation and access to clean water, cholera infections are readily kept at bay. When good medical care is available, the mortality rate stays below 1 percent. It's when conditions are bad that cholera thrives. During the Rwandan genocide of 1994, nearly 80 percent of infected, unaccompanied child refugees in Zaire died within the course of a single month.The world is currently in the midst of the longest running cholera pandemic, which has persisted as it has because the strain responsible manages to hide in people without infection more capably than previous variants. Some estimates put the ratio at 50:1 for carriers to actively infected. It has this year appeared as an exceptionally large outbreak in sub-Saharan Africa. It's also been seen in Vietnam and last fall in Iraq. CDC

Anthrax is a potential bioweapon, according to Dr. Tosh, notable not because of the number of deaths it causes but because “there is so much fear surrounding it.” Anthrax is caused by bacteria that normally live in the soil, but the bugs are also the subject of defense research. People may contract anthrax from inhaling spores, touching the bacteria if they have an open cut, being exposed to dead animals that were infected, or eating infected meat.Today, in the United States, this kind of infection is extremely rare, and anthrax scares are more often linked with bioterror events, like the 2001 attacks which caused 22 infections and five deaths, notes the National Institutes of Health National Library of Medicine. Inhalation of anthrax spores is the greatest fear, which can leave a person sick with pneumonia very quickly. There is a vaccine, but it is typically only given to people who were exposed or are at the highest risk of anthrax infections. Antitoxins and antibiotics like ciprofloxacin, doxycycline, or amoxicillin treat anthrax infections, according to the Centers for Disease Control and Prevention (CDC), but these must be taken quickly after exposure to be effective.