Scientists and health experts at the World Health
Organization and Centers for Disease Control are constantly on guard against
diseases that could sweep through the human population. Which pandemics are
they most worried about, heading into 2014?
H5N1 Influenza
The strain of influenza commonly called bird flu is
technically HPAI A(H5N1), a specific highly pathogenic strain. It’s common in
avian populations, but can be transmitted to humans. This is probably the most
serious pandemic threat on Earth due to several factors.
First, its reservoir
population (animals that host the disease and spread it to other species) is
huge and widespread, found on poultry farms and in live bird markets. Second,
when humans are infected, chances are they will die. The WHO reports a 60
percent mortality rate.
The worst part about H5N1 is that it mutates quickly and
easily, incorporating DNA from other influenza strains it may encounter (in
individuals infected by multiple strains).
Currently, H5N1 isn’t passed from
human to human (or does so very rarely), but studies have shown that just a few
mutations could give it this ability. If this were to occur, the resulting
pandemic would have horrific potential to infect millions. There is a vaccine
against it, but the virus could mutate such that the vaccine is rendered
ineffective. For now, H5N1 has been limited to a few dozen cases in humans per
year.
H7N9 Influenza
This influenza strain
first infected humans in 2013. It is not as virulent as H5N1, and the mortality
rate isn’t as high. However, it has caused a great deal of concern among public
health authorities. No one is quite sure why H7N9 suddenly started infecting
humans. Our limited understanding of it means we have fewer defenses against
it.
There is some evidence that H7N9 already has the ability to be transferred
between humans. Research with ferrets (which can transmit respiratory viruses
to each other in a similar fashion to humans) shows ferret-to-ferret
transmission, and in the Shanghai outbreak it appears that some victims may
have transmitted it to their family members.
Nipah Virus
Nipah is one of several viruses hosted by bats and flying
foxes (others include Marburg Virus, Ebola, and Hendra Virus). It is most often
spread when pigs eat fruit contaminated by bat saliva or urine. The pigs then
spread the disease to humans. During a 1999 outbreak in Malaysia, 1 million
pigs were culled to prevent further infections.
Nipah seems to mutate rapidly,
moving from encephalitic symptoms (brain inflammation, often leading to death)
to respiratory symptoms in later cases. The respiratory form enables human-to-human
transmission. Many outbreaks have a mortality rate of 90 percent or more —
2011 outbreak in Bangladesh killed 21 children. If you want an idea of what a
widespread Nipah pandemic might look like, the virus in the movie Contagion was modeled on- it.
MERS
MERS (Middle East Respiratory Syndrome) is a coronavirus,
named for the spiky proteins that stud its surface. It’s closely related to
SARS, which caused a major scare in Toronto and other cities in 2003, after
outbreaks in China the previous year. MERS also seems to be hosted by bats,
possibly using camels as an intermediate before transmission to humans. MERS is
already capable of human-to-human transmission, and new cases continue to
emerge, suggesting MERS won’t be a “Middle East problem” for much longer.
MRSA
Methicillin-resistant Staphylococcus aureus is a strain of
bacteria that has evolved resistance to a wide range of antibiotics, making it
extremely difficult to treat. MRSA is potentially deadly – in fact, it is
responsible for more deaths than the viruses on this list combined. It can be
controlled with proper sanitation and isolation techniques, and is not more
virulent than other bacteria strains. However, it is so difficult to treat that
“outbreaks” can occur in prisons, hospitals, schools, and among other
vulnerable populations. New strains have shown resistance to additional
antibiotics, which raises the possibility of a bacterial infection that is
literally untreatable. In fact, such cases already
occur with some regularity.
Sources:
Centers for
Disease Control. “Middle East Respiratory Syndrome.”
Hesman Saey, Tina. “Year in Review: a Double Dose of Virus
Scares.” Science
News, Dec. 21, 2013.
USAID.
“Emerging pandemic Threats Program.”
Photo: Irwin Fedriansyah/AP
