Types of Zombie Diseases
Let us talk about
Real zombies diseases, first let us decide
what are the symptoms of being a zombie actually
are. Obviously, the big
one - you know, being literally, actually (un)dead - isn't something with any
real world medical parallels, so we'll just have to restrict ourselves to
diseases that make people
act like the walking dead. That would
include traits like rotting or dead flesh, a trance-like state that would rob
people of any sign of higher cognitive function, an inability to communicate in
anything more than moans and grunts, a slow, shuffling gait, and (if we're
really lucky) a taste for human brains, or at the very least the desire to bite
people.
Sleeping sickness
Sleeping sickness
is the stuff nightmares are made of. The headline
of this BBC News article from 2005 pretty much says it all: "The disease
that makes people zombies." Prevalent in Africa, sleeping sickness is
caused by the parasite
Trypanosoma brucei and transmitted by the
tsetse fly
Worse, there are still no vaccines or ways to prevent infection occurring
once the tsetse fly bites a person. Even the available treatments are - to be
charitable - less than perfect. Melarsoprol is one of the few treatments
available (and that rather dubiously assumes that the average infected person
has access to
any medical care), but it's over fifty years old and
contains enough arsenic to kill 1 in 20 people that are treated with it. And
even if a patient survives the ordeal, they remain at risk of contracting the
disease
again later.
About 50,000 to 70,000 people die of sleeping sickness every year, although
Krishna suspected that estimate was actually much too low. In Uganda, one in
every three people is at risk of getting the disease, and some sixty million
people remain under constant threat. So then, there are about 50,000 examples
of the walking dead each year, although (perhaps mercifully) they don't remain
walking for very long.
Rabies
There isn't a disease, be it mental or physiological, that makes people want
to eat other people, at least none as currently recognized by medical science.
(Cannibalism isn't considered a mental illness in its own right, but rather as
a part of a larger web of psychoses.) There are certain culture-specific mental
conditions - Wendigo
psychosis, observed in certain native American peoples, is one of the
better examples - that make people
think they are turning into
cannibals, but that's about it.
Still,
rabies can, under certain conditions, approximate some of the conditions of the
zombie lust for brains. The rabies virus causes massive inflammation, or swelling,
of the brain, and it's most often transmitted by bites from infected animals.
About 55,000 people die annually from rabies, with almost all of these deaths
occurring in Asia and Africa. Although vaccines do exist (indeed, it was Louis
Pasteur's successful treatment of a rabies-infected child that brought us into
the
modern age of vaccinations), they have to be administered before the onset
of symptoms if the patient is to survive.
Again, the symptoms of rabies sound rather like those of the walking dead:
full or partial paralysis, mental impairment, agitation and strange behavior,
mania, and finally delirium. It takes a bit of cherry-picking of symptoms, but
one could put together a rabies patient with an inability to think clearly or
communicate, difficulty walking, and manic aggression that takes the form of
frequent attacks on humans.
Necrosis
Those of you who are up on your Greek roots already know where we're going
with one: necrosis is death, specifically those of individual groups of cells
before the organism as a whole dies. This isn't technically a disease but
rather a condition with a lot of different possible causes. Cancer, poison,
injury, and infection are all possible causes of premature cell death.
If we're being super-literal about what the walking dead really are, then a
patient with necrotic tissue is maybe the closest equivalent. After all, a
patient suffering from necrosis technically is partially dead, albeit still
very much alive in all the important areas (the brain, the heart, and the rest
of the vital organs, for a start) that we generally associate with the living.
Whatever its external (or, in the case of cancer or infarction, internal but
extraordinary) cause, necrosis triggers a series of event that can lead to even
greater negative effects outside the affected area. The dead tissue stops
sending signals to the nervous system, and necrotic cells can release dangerous
chemicals that hurt nearby, still healthy cells. If the lysosome membrane
inside the cells is damaged, enzymes can be released that can also harm
surrounding cells.
This chain reaction can cause the necrosis to spread (and if it spreads over
a great enough area, it becomes gangrene) and can ultimately be fatal. The only
way to cure the condition is through a process known as debridement, which is
simply the removal of necrotic tissue. If the dead area is too large, this may
require amputation.
Dysarthria
Let's take a bit of a break and talk about something relatively less
serious. ("Relatively" being very much the key word there.) We've
talked about possible causes of zombie-like trances, cell death, and
hyper-aggression. What about something a little more innocuous, like the iconic
moans and grunts of the oncoming zombie horde? What could cause
that?
Well, the best real-world equivalent is probably dysarthria, which is a
disorder affecting the motor controls of human speech. Dysarthria is
particularly appropriate because it's neurological in its origins, which ties
in with the brain-based aspects of zombie lore. There are a lot of different
causes of dysarthric speech, but all are characterized by a malfunction in the
nervous system that makes it difficult to control the tongue, lips, throat, or
lungs.
This in turn causes difficulty in articulation, which can
take the form (among many possible manifestations) of an inability to
communicate in more than unintelligible noises. The condition can be brought on
by traumatic brain injury, metabolic diseases like Lou Gehrig's or Parkinson's,
or a stroke, all of which lead to a loss of control over the vocal muscles.
Possible affected areas include the ability to regulate the volume of speech,
the ability to create the proper inflection, and, most importantly for our
purposes, the ability to create the correct sounds of speech.
Leprosy
Both zombie folklore and leprosy have a long, long history. Armies of the
flesh-eating undead can be traced all the way back to the roughly tenth century
BCE Akkadian work
The Epic of Gilgamesh, which drew on earlier
Sumerian mythology and was one of the first substantial written works in human
history. Cases of leprosy have been reported going back some four thousand
years throughout Eurasia and northern Africa, including China, India, and
Egypt. Considering a common feature of zombies is their rotting flesh and
decaying body parts, it would seem like leprosy and its similar-sounding
symptoms would be a natural inspiration for such stories.
Well...sort of. The truth is (as usual) rather more complicated. First of
all, it's a myth that leprosy causes body parts to rot away and fall off -
indeed, there really aren't any diseases that can actually make limbs fall off
(although, as discussed earlier, necrosis can necessitate the amputation of
dead limbs). Leprosy
can cause damage and numbness in its victims,
which could cause a slow, shuffling walk that might have inspired the gait that
we associate with zombies. The main external symptom of leprosy is the outbreak
of extensive skin lesions, which gives the skin a diseased, decaying appearance
not unlike that of the common conceptions of zombies.
Fortunately, leprosy is pretty much under control at this point, certainly
compared to sleeping sickness. Over 95% of people are naturally immune to the
disease, and over fifteen million people have been cured of the disease in the
last two decades. It's a remarkable turnaround for once of the most feared and
stigmatized diseases in human history - indeed, for centuries leprosy evoked
the same kind of irrational dread that we might now feel towards the dead rising
from the graves en mass, ready to devour our brains.
If you know more ways to become a zombie, feel Free to share your views in Comments section below
