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





Pink Eye!

12 01 2012

Evening time. Your little moppet is fed, bathed, and snuggled ‘neath her blanket. You bend to kiss her nose and then, because your mother did the same, you gently press your cheek against your child’s and exchange butterfly kisses.

This is also known as giving (or getting) the gift of pink eye.

In case you haven’t yet experienced it, pink eye is when your eye becomes pink or red because it’s irritated or inflamed.

We all have a thin membrane that covers the inside of our eyelids and the whites of our eyes – it’s called the conjunctiva. When it becomes inflamed or irritated, we have a case of conjunctivitis. Also known as pink eye.

Lots of non-infectious agents can irritate the conjunctiva and cause our eye to get pink. If we’re allergic to pollen or pet dander, that can give us pink eye. Sometimes the chlorine in pools will do the same.

We can also pick up a bacterial or viral infection that results in pink eye and is infectious, easily spreading person to person. That’s the one that is the gift of the butterfly kiss, should one of the eyes doing the kissing be infected.

Prevention is easy, mostly it’s about not touching your eyes with unclean hands and not sharing any items that have been near an infected person’s eye, such as pillowcases, towels, makeup. You get the idea.

If you have pink eye, do all of the above, and don’t use the same eye dropper or bottle on infected and uninfected eyes, as it’s a good way to ensure both of your eyes become infected. And, CDC says to stay out of swimming pools.

Treatment of conjunctivitis depends entirely on the cause of the irritation. If it’s viral, the symptoms are treated and antivirals may be used for severe cases.

Bacterial infections will probably receive antibiotics and treatment to alleviate the discomfort.

It’s best to check with your provider for specifics, and to make sure and revisit the clinic under these circumstances noted by CDC:

  • Conjunctivitis is accompanied by moderate to severe pain in the eye(s).
  • Conjunctivitis is accompanied by vision problems, such as sensitivity to light or blurred vision, that does not improve when any discharge that is present is wiped from the eye(s).
  • Conjunctivitis is accompanied by intense redness in the eye(s).
  • Conjunctivitis symptoms become worse or persist when a patient is suspected of having a severe form of viral conjunctivitis—for example, a type caused by herpes simplex virus or varicella-zoster virus (the cause of chickenpox and shingles).
  • Conjunctivitis occurs in a patient who is immunocompromised (has a weakened immune system) from HIV infection, cancer treatment, or other medical conditions or treatments.
  • Bacterial conjunctivitis is being treated with antibiotics and does not begin to improve after 24 hours of treatment.

One of the best methods of disease prevention (and not just pink eye) is to keep our hands clean and not touch our noses, eyes, or mouth.

I have to confess that, although my teenager no longer tolerates butterfly kisses, my tweener loves them. As long as the whites of her eyes remain, well, white, we will share that bedtime ritual. But, I do perform a quick inspection as I’m leaning in, just in case.

By Trish Parnell

Image courtesy of littlenelly





Bacteria and Viruses-How They Work

19 05 2011

Bacteria
There are thousands of types of bacteria and most are harmless or even beneficial.  However, even “good” bacteria, if they find their way to the wrong place, can cause harm.  For example, bacteria that live in our mouth can cause illness if they find their way to the middle ear and cause an ear infection.  Also, some bacteria that ordinarily do not cause disease in persons with a working immune system, may do so in people with a weakened immune defense system.

Most bacterial diseases occur when bacteria multiply rapidly in tissue, damaging or killing it.  Boils result from the multiplication of bacteria in the skin.  Other bacteria cause disease by producing toxins or poisons.  Tetanus is a disease that begins after bacteria that normally live in soil enter the body through a wound.  The bacteria produce a poison that affects muscles and nerves far away from the wound.

To cause illness in humans, bacteria need to be able to gain access to the human body, reach their unique place within the body and multiply there.  The human body has developed several strategies to make life as difficult as possible for disease-causing or pathogenic bacteria, but bacteria have also learned how to break down our defenses.

An infection by pathogenic bacteria can be seen as a miniature battle between bacteria and host.  Bacteria try to survive and feed and multiply, while the human body’s immune system tries to prevent this.  The resulting infection is a process with three possible outcomes:

  • The immune system wins and the bacteria are removed, possibly with the help of medications.
  • The bacteria win the ultimate battle and kill their host (bacterial infections are a major cause of death, especially for children and elderly people).
  • An equilibrium is reached in which host and bacteria live in relationship together and damage is minimized.

Viruses
All viruses live to make more viruses, and they usually make more viruses by invading a host’s cell (for instance, one of the cells in our bodies) and using the host cell’s “machinery” to churn out more of themselves.

Once the viruses mature, they leave the host cell and go find many more host cells to set up shop in so that they can start churning out more of themselves.

Sometimes, there is a hitch in the churning process.  During viral replication, mutations can occur.

The mutation can be bad enough to interfere with the virus’s ability to duplicate itself.  Or, it might just create a new strain of the virus.  The influenza virus does this, which is why every year, each new strain of flu virus must be identified in order to make a vaccine that is effective against it.

Humans are able to fight off viruses in several ways:

  • Proteins called interferons help neighboring cells resist infection by the virus.
  • If interferons fail, the immune system kicks in and fights the infection by killing the virus floating around outside the host cells and killing infected host cells.  (HIV is the exception, because HIV infects cells of the immune system that are necessary to kill the infected cells.)
  • There are drugs that help the body fight certain viral infections.  They hinder or stop the replication of the virus and are known as antivirals/retrovirals.

This is one in a series of excerpts from PKIDs’ Infectious Disease Workshop.  We hope you find the materials useful – the instructor’s text and activities are all free downloads. 

Photo credit: measles – sanofi pasteur





Medical Tourism is Risky

14 10 2010

Skyrocketing healthcare costs in the U.S. have been a boon to medical tourism, with eager patients globetrotting for anything from cosmetic surgery to organ transplantation.

These “medical tourists” often believe they will receive quality care at affordable costs, with the added benefit of recuperating in a vacation spot.  It sounds too good to be true, doesn’t it?  That’s because it often is.  The quality care they seek may not be what they get.

There are several reasons to pause before packing, including ethical concerns related to organ and tissue donor sources, and legal and physical issues should one be harmed rather than helped by the procedure and follow-up care.

Another worry includes the potential for infection with a superbug that is resistant to most drugs.  Traveling patients could be bringing home serious infections along with their newly formed scars.

Currently, the number of identified cases of infection with a superbug in the U.S. is small.  However, the potential for antibiotic-resistant bacteria (the superbug) to grow in dominance is real.  There has been some success in treating these superbugs with an older drug (Colistimethate), but this drug has a number of toxic side effects.

Potential medical tourists need to ponder the risks, including exposure to a drug-resistant superbug that may not only endanger them, but also contribute to a global public health problem.





Dr. Mary Beth Explains Fifth Disease

16 06 2010

Dr. Mary Beth, PKIDs’ advice nurse, tells us what Fifth disease is and that we can’t really prevent it! But, we can manage symptoms.

Listen now!

Right-click here to download podcast (9min/4.5mb)





STDs

18 02 2009

The Centers for Disease Control and Prevention (CDC) reports that new cases of common sexually transmitted diseases (STDs) are on the rise in the United States. 
 
Almost 19 million of these new infections occur each year, and about half of those infected are between the ages of 15 and 24.  This is the age group that usually bears the brunt of new infections, with women and minorities more likely to be affected. 

About 10 years ago, the CDC began an all-out national effort to eliminate syphilis as an ongoing health problem and nearly succeeded, but the last two years have shown an increase in infections, rather than the expected decrease.

CDC surveillance indicates that reported cases of chlamydia and gonorrhea together surpassed 1.4 million in 2007.

As with so many types of infections, someone can look perfectly healthy but be living with one of these diseases.  If you’re sexually active, get tested a couple of times a year.  Don’t be shy about asking your healthcare provider to test you.  It’s better to identify and possibly treat an infection than let it go until it causes potentially serious and long-term health problems.

Take control of your life.  It’s the only one you’re going to get!

The report, “Sexually Transmitted Disease Surveillance 2007,” can be found at http://www.cdc.gov/std/stats07/toc.htm for those interested in delving deeper into this subject.