To and Fro and In-between (or Help! I'm afraid to breathe!)

Besides diseases in other countries, every traveler has another fear-being trapped in an aircraft cabin for several hours with the passenger that can't stop coughing. Every year over 1 billion people travel by commercial airways from all over the world, and this number is expected to double over the next 20 years.  But how likely are you to get sick from that passenger who didn't change their flight (or at least their seat next to you)?

Droplet transmission.
Image courtesy of the CDC.

The answer is a complex one because there are multiple ways to get infected. One method of infection (and the one everyone worries about on flights) is droplet or airborne transmission.  This occurs by inhaling small particles containing infectious agents that remain infective over time and distance. 

Surprisingly, the risk of infection on an airplane via this route is lower than you might think.  All commercial aircrafts (and a few modified older planes) recirculate 10-50% of the air in the cabin and mix in the air from outside.  The recirculated air passes through a series of filters 20-30 times per hour.  In newer-model airplanes, high-efficiency particulate air (HEPA) filters capture 99.9% of particles 0.1-0.3 um in diameter.  Also, the air isn't forced up and down the length of the airplane, but rather flows transversely across the plane in limited bands (saving you from that coughing passenger several rows ahead).  

Seating diagram for passengers
exposed to measles, rubella, or TB.
Image courtesy of the CDC.

If the sick passenger is sitting next to you, the risk is about the same as sitting next to any other ill person (the odds of infection

change depending on what is making the person sick).  The good news is that there is protocol in place should the disease they carry be of public health concern.   Flight contact investigations are performed for infectious tuberculosis (TB), measles, rubella (German measles), pertussis (whooping cough), and meningococcal disease (meningitis).  CDC protocols are in place to identify passengers who may have been exposed.  Exposed passengers will be contacted by their state and local health departments or ministries of health to inform them about their exposure and what to do.

So take a deep breath, relax, and enjoy the flight (and try not to think to hard about what you might be touching...)

Dengue World Cup

Endemic Regions of Dengue Fever  
Image courtesy of the CDC

Dengue fever infects approximately 400 million people annually and is a leading cause of illness and death in the tropics and subtropics.  It was first documented in the 1950s in

Aedes aegypti mosquito, a dengue virus vector.
Image courtesy of the CDC

the Philippines and Thailand and remained there until 1981, when large numbers of Dengue Hemorrhagic Fever were reported in the Caribbean and Latin America, including Puerto Rico, the U.S. Virgin Islands, U.S.-affiliated Pacific Islands and the British Virgin Islands. Yet only recently has it begun making headlines, thanks to the 2014 FIFA World Cup in Brazil.  

Dengue fever has 4 virus types (DENV 1, 2, 3, and 4) and is spread by the Aedes mosquito in high population areas when rainfall is optimal for breeding.  It is a bloodborne virus, so transmission can also occur through exposure to infected blood, organs, and tissues, as well as through vertical transmission (mother-to-neonate).  Dengue hemorrhagic fever is a more severe form of dengue fever, and risk factors include having a previous infection, being younger than 12, female, or Caucasian. 

Dengue fever may cause high fever, severe headache, eye pain, joint pain, muscle and/or bone pain, rash, mild bleeding in the nose or gums, petechiae, easy bruising and/or a low white blood cell count.  Warning signs to watch for 3-7 days after fever temperature declines include severe abdominal pain or persistent vomiting, red spots or patches on the skin, bleeding from the nose or gums, vomiting blood, black stools, drowsiness or irritability, pale, cold, clammy skin, or difficulty breathing.  The signs and symptoms of DHF are consistent with dengue fever, including the fever decline.  In DHF, this decline marks the beginning of a 24-48 hour period where capillaries become excessively permeable, causing ascites and pleural effusions.  Without prompt, appropriate treatment, symptoms can progress to circulatory system failure and shock, and possibly death.

Currently, there is no vaccination or specific medication for treatment of dengue fever or dengue hemorrhagic fever.  Symptoms are manageable with analgesic pain relievers (ex. acetaminophen and paracetamol), rest, plenty of fluids to prevent dehydration, and consulting a physician.  DHF can be effectively treated with fluid replacement therapy with an early clinical diagnosis (this generally requires hospitalization).

There is good news on the horizon.  Sanofi Pasteur, a multinational pharmaceutical company, is

in Phase 3 clinical trials of the CYD dengue vaccine. The purpose of the study is to assess the efficacy of the CYD dengue vaccine after 3 vaccinations at 0, 6, and 12 months in preventing symptomatic virologically-confirmed dnegue cases, regardless of the severity, due to any of the four virus types in children aged 2 to 14 years.  It is difficult to determine at this time when this vaccine would be available to the public.  For more information, please visit www.clinicaltrials.gov 

Prevention

To prevent dengue fever when present in endemic regions, eliminate containers that hold water in and around the home to prevent breeding. Wear mosquito repellent indoors and outside (the higher the DEET content, the better) at all times and long sleeves and pants.  Windows and door screens should be secure and without holes, and use air conditioning where possible.

For a more technical review: Dengue Detection

A New Respiratory Tract Infection

MERS-CoV particles under negative stain electron microscopy
Virions contain club-like projections emanating from
 membrane. Image courtesy of CDC

    

Human serum antibodies react with MERS infected  Vero cells,
indicating infection.  Image courtesy of CDC

There's a new kid on the block among respiratory tract infections, and it goes by MERS, or Middle East Respiratory Syndrome, first confirmed in Saudi Arabia in 2012.  Symptoms of infection include fever, cough, and shortness of breath, all signs of severe acute respiratory illness.  Its mortality rate is greater than 30% for those infected. 

This syndrome is caused by a coronavirus called MERS-CoV.  Coronaviruses, named for their crown-like morphology.  They are common viruses and usually cause mild to moderate upper-respiratory tract infections. There are three main subgroups and a recently-assigned new sub group, alpha, beta, gamma, and delta, respectively. 

 The ones that affect humans are alpha 229E and NL63, and beta OC473, HKU1, and SARS-CoV (responsible for severe acute respiratory syndrome prior to 2004).  Typical symptoms of non-SARS coronaviruses are coughing, runny nose, sore throat, and fever.  It may also cause lower-respiratory tract infections in the elderly and immunocompromised

Why is this virus important? Because like SARS, it has left its origin country and infected two U.S. patients that had traveled to Saudi Arabia--one on May 2nd, 2014 and a second one May 11th, 2014.  The first patient has made a full recovery and the second is currently hospitalized but recovering. Don’t panic--at this time there is a low risk to the general American public at this time and those that had contact with the two infected are being contacted.  

For more information, please visit: CDC.gov

For a more technical review of this topic: MERS-CoV Interim Guidelines

Update 5/15/15: healthcare workers exposed to the MERS patients have been sent home for 14 days after two showed flu-like symptoms. Neither are confirmed MERS patients as of now. 

Resource: CNN.com