Ask Emily

26 04 2012

What’s the deadliest infectious disease ever and what currently is the most deadly infectious disease?

The answer to this question is more complex than simply counting up numbers of people who die from infection. For example, diseases like measles and smallpox have proved to be far deadlier in some populations—such as Native Americans—than in others, because of population differences in disease resistance.

Another variable is intensity of the illness a pathogen causes. Influenza comes in many forms of virulence, and as the Spanish flu pandemic of the early 20th century made clear, even that virulence can vary depending on specific population features; the Spanish flu, which took an estimated 50 million lives, killed the young most relentlessly.

Even an individual disease vector can wax and wane in terms of how virulent it is or which tissues it invades. For example, Yersinia pestis, the bacterium responsible for the infamous Black Death that swept through Europe in the 14th century, may vary over time in its virulence and is far more deadly when transmitted as an aerosol to lung tissues than when it invades the lymph and causes the bubos that characterize it.

Another issue is, how do we calculate “deadliest?” Is it in terms of sheer overall numbers, or do we calculate it in terms of how many people it kills among the number infected? For the sake of addressing this question, let’s talk about both.

Historically, in terms of sheer numbers, the deadliest diseases were smallpox, measles, tuberculosis, plague (e.g., the Black Plague), and malaria. According to a handy Website, the Book of Odds, which calculates odds for us, measles has killed about 200 million people worldwide in the last 150 years and still kills hundreds of thousands in the developing world. Thanks to vaccines, the odds of contracting measles in the United States today are very low unless you are an unvaccinated person living in areas where vaccine uptake is low.

The story on smallpox is similar—it may have killed more people by percent or sheer numbers than any other infectious disease in history, including 300 million in the 20th century alone by some estimates. Yet smallpox as an infectious disease no longer exists thanks to its total elimination through vaccine campaigns.

Thus, along with the plague, smallpox and measles have, for millennia, been the historical killers of humans and would still be among the deadliest infectious diseases today were it not for vaccines. What we have left are some old killers on the list—tuberculosis and malaria—and a newer entity, HIV, the virus that causes AIDS.

We have yet to develop efficient vaccines against any of them. According to USAID, in terms of absolute numbers of deaths, AIDS kills the most people each year, with 2.8 million AIDS-related deaths in 2004, followed by tuberculosis and malaria.

Indeed, AIDS and tuberculosis are often co-conspirators in death, as infection with the HIV virus makes people 20 to 30 times more likely to develop active TB with TB infection. Research for vaccines against HIV and malaria has been feverish but as-yet incompletely successful, one reason these diseases remain the top global killers.

But what about the deadliest disease in terms of how many of infected people die? In the absence of effective treatment, HIV might be one candidate. But the ones that come first to mind are the viruses that cause fast-moving hemorrhagic fevers, such as the Marburg or Ebola viruses.

The Marburg virus, named for the location of the first outbreak and a virus that may reside without symptoms in fruit bats, has caused death rates as high as 90% in some areas, although the average is 23–25%. It is a filovirus, in the same viral family as the five Ebola viruses. One of the Ebola viruses, Ebola-Reston, is perhaps the most notorious of the hemorrhagic fever viruses, having led to death rates as high as 89% in outbreaks.

A near-100% mortality rate is about as deadly as an infectious agent can be if that’s the measure of “deadly” we’re using.

By Emily Willingham

Image courtesy of Wikimedia Commons

The end in sight – eliminating seven diseases plaguing half a billion kids

5 04 2012

(Welcome to End7. Thank you for sharing information about your work through this guest post!)

Moms and Dads from every country want one thing; healthy kids.  That’s why groups like PKIDs form—to help educate parents and the general public about specific diseases and to provide families with the support they need.

While the languages, food and clothes may be quite different for some of the kids we work with, we have a lot in common with PKIDs. Unfortunately, for families living in the poorest communities in the world, there is little in the way of support networks or treatment programs for children and adults who have neglected tropical diseases—or NTDs.

NTDs are a group of parasitic and bacterial diseases that infect half a billion kids around the world, most coming from families living on less than a $1.25 a day. These kids don’t always have shoes or clean water, which is a problem since they can get NTDs just by doing the things that kids love to do—playing, swimming and other daily activities.

When kids get sick with NTDs like hookworm, whipworm and roundworm, parasitic worms grow in their stomachs, robbing them of food and energy and making them too weak to pay attention in school. For those who live near water sources, flies may carry a disease called River Blindness, which causes rashes and severe itching and can eventually lead to blindness. These NTDs disable and debilitate their victims, keeping children out of school and preventing parents from working. They take away any chance that families have of lifting themselves out of poverty.

But this is a major global health issue that actually has a simple, cost-effective solution.  It costs just 50 cents for a packet of pills that treats and protects a child for a year. Since the drugs are donated by major pharmaceutical companies, we just need the funds to get them to the people that need them most and set up treatment and education programs that communities can run themselves.  Even better, the medicine is so easy to administer that communities don’t even need medical professionals—who are often in very short supply in developing countries—to administer them to sick kids.  The medicine can be dispensed right in schools or community centers.

The END7 campaign is working to raise awareness and donations in order to actually eliminate seven of these NTDs by 2020—the WHO said it could be done and we accepted the challenge.

To learn more about NTDs and to join the movement to eliminate them, visit our campaign on  Facebook and tell your friends to do the same. We need help in taking the “neglected” out of NTDs and that starts with you.

Together we can see the end.

By Mara Veraar, Social Media Officer at Sabin

Image courtesy of Esther Havens

Rare Diseases Matter

2 02 2012

(We welcome David Bradley Science Writer as our guest blogger. Thanks, David!)

Pharmaceutical research and development has improved our quality of life and boosted life expectancy significantly over the last few decades.

We are living longer, healthier lives thanks to medical science. Although there are concerns about drug resistance and so-called superbugs, vaccination, antibiotics and antiviral drugs are incredibly successful at keeping diseases at bay and reducing significantly the risk of death from infection following a surgical operation.

In addition, important medical advances have made cancer treatable and reduced the risk of dying from heart disease significantly. The emergence of diseases of old age, such as Alzheimer’s disease, reflect not a failure on the part of medicine, but the fact that so many people reach old age rather than dying young of the illnesses to which our ancestors succumbed for lack of medicine.

There remain, nevertheless, many lesser-known and rare diseases for which there are no treatments. The US Rare Diseases Act of 2002 defined rare diseases based on prevalence. Any condition afflicting fewer than 200,000 people in the US (about 1 in 1,500) was labeled rare.

The Europeans by contrast defined these diseases based on how much of a threat to life they represent. Whatever the definition, the pharmaceutical industry is beginning to home in on these rare diseases, which is obviously good news for sufferers.

Orphanet, which as the name might suggest is an online portal for information about rare diseases and orphan drugs, suggests that, “There is no disease so rare that it does not deserve attention.”

Moreover, just because a disease is labeled rare does not mean that there are not large numbers of people affected. There might be 10,000 patients with any given “rare” disease in the US alone. The numbers might be in the millions if we consider worldwide incidence.

Orphanet’s Segolene Ayme told me: “The true prevalence of rare diseases is unknown, there is no source of data at population level.” In fact, the data are often skewed towards more conservative estimates of disease incidence, although for some genetic diseases, the numbers may truly amount to a few dozen people rather than tens of thousands.

The list of rare diseases is vast and continues to grow as new health problems are identified for the first time as distinct diseases and disorders. On that growing list are Aarskog syndrome, Gaucher’s disease, tyrosinemia type 1, Kahler’s disease, Q fever, Takayasu arteritis , Waardenburg anophthalmia syndrome and Zygomycosis.

Andreas Zaby of the Berlin School of Economics and Law, in Germany, has analysed the impact of legislation aimed at stimulating R&D into these and other diseases. He says there is a great deal of room for improvement in addressing the problem of rare diseases and suggests that the creation of expert networks could help. He adds that specialist care facilities and reference centers for research and treatment are urgently needed if medicine in these areas is to move forward.

Coordination by the World Health Organization could be the answer to helping medical science tackle a vast range of diseases, each of which afflicts a limited number of people but taken as a whole cause misery and suffering for millions worldwide.

Rare Disease Day is 29 February. Let’s all make some noise for those who are too often ignored.

Image courtesy of

Nodding Disease

13 06 2011

Nodding disease attacks kids, usually when they’re between the ages of five and 15.  The infection affects the brain and symptoms include seizures and a lack of physical and mental development. Many children, unable or unwilling to eat, become malnourished and die.

It’s rare—some kids get it, but most don’t. It was reported in Tanzania in the ‘60s, and then Sudan and more recently, Uganda. Because of its rarity (hundreds of cases are reported, not tens of thousands or millions), and location in very poor countries, it’s what’s called a neglected disease.

Epidemiologists aren’t certain of the cause, although they’ve found a possible association with the parasite that causes onchocerciasis (river blindness). This parasite is a filarial worm transmitted by the female blackfly.

If hundreds of kids in Miami, Atlanta and Charlotte were experiencing these symptoms, this disease wouldn’t be neglected. That’s a fact, but we don’t have to live with it. Speak up. Act up. Let’s get some noise going to help these kids.

Contact the Gates Foundation, the Drugs for Neglected Diseases initiative, and the USAID’s Neglected Tropical Diseases program and encourage them to steer funding toward this disease.

Author: Trish Parnell