Wednesday, October 30, 2013

Free Will Ain’t Free

Biology concepts – neural parasitology, domoic acid toxicity 

Zombies don’t have a choice in how they behave. Free will
is a thing of the past; they don’t even have the ability to resist
a dance routine with Michael Jackson. Michael seems awfully
at ease in the midst of the undead. Creepy….yes. Scary…. yes.
A thriller?…..maybe no.
It would be hard to believe that zombies develop a taste for human flesh, especially brains, out of nowhere. It would seem that they don’t have a choice; their activities are decided for them. They’ve lost their free will.

Don’t scoff at this; nature is full of examples where one organism can cause another organism to change its behavior – just think of all the silly things boys do trying to impress girls. But first a couple of stories where a change in behavior has less to do with parasitism.

In August 2013, residents of Moscow began reporting that the pigeons were acting odd. They would walk around in a funk, not get out of the way of traffic, and not fly away from danger. One family reported that their dinner one evening was disrupted by a pigeon on their window ledge that lost its balance and fell into their kitchen.

These zombie pigeons (the pecking dead, as one website called them) were freaking out the population, so the scientists went to work. It seems that many of the dead and affected pigeons were carrying salmonella bacteria and/or had Newcastle disease. The virus that causes this disease, unimaginatively called the Newcastle disease virus (NDV), can be transmitted to humans, so it's a good thing the population got freaked out.

The virus causes the birds to stagger about, stumble around in circles, and turn their heads upside down – much like vodka does in humans. However, when humans get NDV, they most likely will just have a flu-like episode.

Zombie birds also led to a famous movie. Alfred Hitchcock’s classic film, The Birds, is the story of a terrifying attack on a small fishing village by many flocks of different birds. They attacked people, flew into car windows and houses, and caused deaths and damage. Seems silly doesn’t it, being killed by a shore bird? I think I would have them give some other reason in my obituary.

Tippi Hedrin was the female lead in Hitchcock’s The Birds. Hitch
had seen her in some commercials and chose her over Grace
Kelly….. GRACE KELLY! Later on , he developed an unhealthy
obsession with Tippi, and who wouldn’t, with all that running and
screaming and bird doo?
It turns out that the movie was based on a 1961 incident near Monterey Bay, California. The birds went nuts and no one knew why – that makes it creepier. It wasn’t until 1995 when another episode of bizarre behavior in sea lions led to the answer.  The sea lions in 1995 and 2010-11 were acting like zombies as well. They wouldn’t get out of the way of boats or they would come up on land and just keep scooting inland until they died.

In 1987, it was recognized that a toxin produced by certain species of marine algae was responsible for the zombie like behaviors. Called domoic acid, the toxin is produced by the algae and accumulates in marine organisms that feed on phytoplankton or algae that are contaminated. Normally, levels of domoic acid are too low to cause problems, but in years where the algae overgrows, called a bloom, the levels will rise dramatically.

Although the acid seems to have no affect on lower life like shellfish, bigger animals are strongly affected, including humans. When the sea lions or birds feed on contaminated food, they begin to display the bizarre behaviors. In the case of the 1961 birds, there happened to be a collection of samples from the bay that had been kept all these years. Tests on the shellfish and algae samples from 1961 showed high levels of domoic acid.

In a strange coincidence, a new paper has been published about how infections can move through a flock of birds. It uses a mathematical model based on many predictors and factors. The model is called the Zombie-City model, based on how a zombie population might grow in a population of unsuspecting humans. But we want to focus on the loss of free will in nature’s creatures.

Free will in lower animals?  It does exist. Most people believe that the behaviors of insects and such are merely responses to environmental and situational cues, and any variation in behavior is due to misreading of cues or random errors. But studies in fruitflies show that they can pick out their own patterns of behavior when a blank canvas is given them.

The Emerald Cockroach Wasp (A. compressa) is solitary insect,
it doesn’t live communally as many bees and wasps do.  Only
the females have stingers, so making zombies is definitely a
reproductive strategy. In 1941, they were introduced to
Hawaii to try and control the cockroach population, but it
didn’t work. They just don’t lay enough eggs.
One such case of co-opted free will in an insect is the Jewel Wasp (Ampulex compressa) and the American Cockroach (Periplaneta americana). The wasp lives in Africa and Asia, so this isn’t something we could use to get rid of NYC cockroaches. P. Americana isn’t even native to the Americas. It was introduced from Africa as early as 1625, before it was officially named.

What the wasp steals is the roach’s ability to decide if it wants to walk or run. Most wasps sting to kill, but the Jewel Wasp stings the cockroach in the brain, altering its behavior with its venom. A 2010 study showed that the wasp stings the roach continuously for up to three minutes, trying to locate a particular part of the cockroach’s brain.

What it is searching for is called the subesophageal ganglion, the part of the brain that allows the roach to initiate walking and running movements. When that part of the brain is flooded with venom, the cockroach stands still, with no will to begin leg movements. It isn’t paralyzed – it’s just a zombie.

Another study has started to investigate just how the wasp venom robs the cockroach of its will to walk. There is an insect neurotransmitter called octopamine that is released by some of P. Americana’s neurons. It is this transmitter that allows the cockroach to initiate walking.

The study hasn’t pinpointed just how the venom interrupts the octopamine signaling, but they know if they deplete the amines in the brain, they see the same affect. If they add back octopamine, they can rescue the cockroach’s natural behavior. However, the study also showed that the venom doesn’t reduce octopamine levels and it doesn’t prevent is release, so there's still more work to be done.

The wasp first stings the cockroach in the abdomen, just a
quick sting to temporarily weaken the front legs. Then it
stings the brain and when the cockroach stops
moving, it cuts off part of one antenna. I don’t know why. It
grasps the antenna in its jaws and herds to the roach to its nest.
Instead of pulling, they should evolve saddles.
Why does the wasp turn the cockroach into a zombie? I’m glad you asked. Remember, the cockroach isn’t paralyzed, it just hasn’t the will to walk on its own. So the wasp tugs on the cockroach’s antennae and herds the roach into its underground nest. There the wasp lays an egg in the cockroach’s abdomen and the emerging larva feeds on the cockroach until they are ready to emerge eight days later.

So why not just kill the cockroach with the sting and lay the egg? The larva need fresh meat, and a dead cockroach rots in one day. To make the meal satisfactory for the eight days needed, the cockroach must remain alive, but in a state where it can’t attack the wasp or the larva; hence the zombification.

It gets even creepier. The wasps have gotten so good at this strategy that they now go to the trouble of cleaning their meal. A 2013 study shows that the wasp larvae produces several antimicrobial chemicals that rid the cockroach of any contaminating bacteria or parasites as the larvae munch on it. I know I’d clean a zombie before I ate it.

There are several other examples of theft of free will, including a couple of fungi that make ants stop their normal work and climb high in trees to allow for the best spread of the fungal spores as they mature. There’s also a hairworm that forces grasshoppers to commit suicide by jumping into water, just so the worm can complete its life cycle. But I don’t want to leave this subject without hitting the king of neural parasitologyToxoplasma gondii.

The spiny ant is the zombie victim of the O. unilateralis fungus.
When infected, the ant stops doing its job for the colony and
falls out of the tree canopy. After wandering the forest floor, it
will bite the underside of a leaf and never let go. It just stays
there waiting to die. Then the fungus sprouts a fruiting body
with spores out the top of its head, and the spores shoot of
into the air. The low altitude (less humid) and under leaf
position give the fungus the greatest chance to survive. Fossil
evidence shows that this has been occurring for at least 48
million years.

T. gondii is a single-celled eukaryotic parasite that has a complex life cycle. It can reproduce asexual in any of the hosts it infects, but can only reproduce sexually in cats, of all things. This is important because sexual reproduction is an obligate life cycle stage for the parasite and contributes to its evolutionary health.

The parasite has taken steps to insure that it finds its way into cats by changing the behaviors of the mice and rats it finds itself inside. It messes with rodent brain chemistry (since it tends to form cyst organisms in the brain) that makes rodents unafraid of cats. In fact, a recent study found that the organism confuses the rodents into believing that cat urine smells like a potential mate!           

T. gondii activates a certain neuronal transcription factor, which leads to increased production of different proteins in the brain. In rodents and humans, this leads to an increase in dopamine (similar to octopamine in the cockroach) production and a decrease in tryptophan usage.

Because the cysts target areas of the rodent brain that control fear, the change in behaviors are involve, but are not limited to fear. There isn’t any evidence that the cysts have a selective range in the human brain, but considering the changes that occur in men as described below, it is a possibility.

On the left are four T. gondii parasites and on the right are the cysts
that they can form in the brain. Recent ecvidences are showing
that cysts of T. gondii can be linked to increased chance of suicide
attempt and more violent attempts, more depression and
neurotic behavior, and an increased chance of having children
that will develop schizophrenia. In humans, this may have
something to do directly with the parasite, or it may be that high
levels of immune modulators lead to the changes in thoughts and
behaviors. Scary thought, our immune system could drive us
to kill ourselves.
There is a suspicion that T. gondii produces an enzyme that catalyzes the formation of a dopamine precursor. Dopamine is a catecholamine, so it is involved in the fight or flight response; definitely a fear component. The interesting thing is that even a latent (asymptomatic) infection affects men and women differently. Bizarrely, a 2011 study showed that infected men are more attracted to cat urine, while infected women find it less attractive.

In general, men with a long-term T. gondii infection show lower IQs, are taller (about 3 cm on average), and are more likely to break rules, take risks, be jealous, and exhibit anti-social behaviors. Right now – I’m not so proud to be a guy.

On the other hand, women with long-term toxoplasmosis infections tend to be more outgoing, friendlier, more promiscuous, and more attractive to men. Wow, Mars and Venus to the nth degree! The question still remains – how do the forced behavior changes in humans benefit the organism?

Next week, we return to our discussion of nucleic acid exceptions by discussing instances where organisms can rewrite their genetic code.

House PK, Vyas A, & Sapolsky R (2011). Predator cat odors activate sexual arousal pathways in brains of Toxoplasma gondii infected rats. PloS one, 6 (8) PMID: 21858053

Flegr J, Lenochová P, Hodný Z, & Vondrová M (2011). Fatal attraction phenomenon in humans: cat odour attractiveness increased for toxoplasma-infected men while decreased for infected women. PLoS neglected tropical diseases, 5 (11) PMID: 22087345

Banks CN, & Adams ME (2012). Biogenic amines in the nervous system of the cockroach, Periplaneta americana following envenomation by the jewel wasp, Ampulex compressa. Toxicon : official journal of the International Society on Toxinology, 59 (2), 320-8 PMID: 22085538

Herzner G, Schlecht A, Dollhofer V, Parzefall C, Harrar K, Kreuzer A, Pilsl L, & Ruther J (2013). Larvae of the parasitoid wasp Ampulex compressa sanitize their host, the American cockroach, with a blend of antimicrobials. Proceedings of the National Academy of Sciences of the United States of America, 110 (4), 1369-74 PMID: 23297195

For more information or classroom activities, see:

Moscow zombie pigeons-

Domoic acid toxicity –

Jewel wasp and cockroach –

Toxoplasma gondii

Fungal parasites and ants –

Hairworm and grasshopper -

Zombie apocalypse case study for class -

Wednesday, October 23, 2013

The Living Dead - Living Or Dead?

Biology concepts – characteristics of life, cell theory, reproduction, homeostasis, evolution

How could this monster have come from the Walking Dead
TV show? In what way is he/she walking, and while
she is in dire need of a makeover, can you 
consider her dead?
A popular zombie TV show is called, "The Walking Dead." The George Romero films call zombies the “living dead.” Can you say that corpse-like people have life? Let’s recall our two varieties of zombies we talked about last week, those that were dead, but have been reanimated (brought back to life), and those that haven’t died specifically, but exhibit zombie behaviors.

In either case, they are moving and eating and moaning, and generally disrupting the social order. So are they forms of life? To answer the question, we first have to ask what it takes to be considered alive. What characteristics of living things separate them from non-living things?

Don’t laugh, it’s not always so easy to tell if something is alive or not. There have been several different systems for defining life, everything from mechanism, which says life is just a special set of chemical reactions, to vitalism, which says life consists of a vital force all its own and doesn’t obey the laws of physics.

Philosophers and scientists in history have searched for a single attribute definition of life – the one thing that separates all life from all non-life, but it hasn’t been very successful. How about, “livings things die?” Although it sounds sexy at first, this isn’t a very helpful definition.

Death is just an absence of life, so wouldn’t you need to define life first? Anyway - living things can die, but that doesn’t mean they must die. There is a species of jellyfish, Turritopsis dohrnii, which very well may be immortal. Most jellyfish start out as an immature polyp which develops into a medusa (the bell shape with all the trailing filaments). Then they get old and die.

This is the medusa form of T. dohrnii. The many hairs have
nematocysts to capture prey, while the red area contains
what nervous tissue the animal has, as well as the digestive
system. At any point in its life cycle, it can regress to its
infant form (polyp) and then send out clones of itself and
grow up again. It would be is if you and your parents were
the same age!
But T. dohrnii can revert from medusa to polyp and then start the process all over again. It’s hard to say that they are truly immortal, they can still get eaten or sick, and how would we know if they did live forever; have you ever done anything forever?? Wait - downloading a movie on a 2009 MacBook Pro takes forever.

Think about the number of exceptions to biologic rules we have discovered together in the past couple of years. Do you really think there can be one attribute of living things to which there is no exception, counter-example, or borderline case?

Some scientists say that we can't define what constitutes life because, as of now, we are limited to knowing only life on Earth. Life elsewhere may be completely different. But according to this line of thinking, you could never define life, because you couldn’t ever know if you had found every candidate in the universe.

For now, a list of characteristics that living things all possess and non-living things do not is most appropriate. Some folks use four characteristics, some five, six, seven or eight. I tend to go with a seven characteristic set, because that’s the number of items that most people are able to remember. You think it’s a coincidence that telephone numbers are seven digits?

Let’s take a look at the seven characteristics and see how many are fulfilled by zombies.

Cells – Living things are made of cell(s). This has been well discussed for hundreds of years and we haven’t found any exceptions to this rule. In fact, scientists have extended the idea of cells even further. Called the cell theory, the idea is that life is made of cells, the cell is the basic unit of life, and all cells come from other cells. Anyone disagree?

The top left image is of a piece of cork as Robert Hooke
would have seen it in his microscope. The right top image
is a higher power microscope image of cork. Hooke thought
the empty spaces looked like the empty rooms of monks
(below), so he called them cells. In cork, you are really seeing
the remnants of cells, only the cell walls are left.
Cell theory didn’t come about all at once. Different scientists added different parts, including Rudolph Virchow, the father of modern pathology (pathos = disease, and ology = study of).  The TED video series has a good video about the weird history of the cell theory, including how Virchow’s contribution was probably stolen from someone else.

Organization – Livings things are organized at one or many levels. Even a single-celled organism has organization. It has a membrane to keep it’s insides inside, and everything else outside. This is organization. A bacterium has a single (usually), large circular DNA on which is has coded all its genes. That’s organization.

Multicellular organisms inherently have more organization, since they have cells that must communicate with one another and start to have specialization of function, but all cells must transfer their hereditary material, and this requires great organization.

A new review has started to collate the evidence that this complex organization extends to the nucleus-less bacteria. It seems that bacterial RNA functions are sequestered in specific parts of the cell. These spatial relations seem also to affect the functions of the cell, so even at the lowest level of biologic organization, there seems to be a lot going on.

Biologic organization moves from small to big - cells, tissues, organs, organ systems, organisms. Bacteria jump straight from cell to organism, but we can go further. We can start with individuals and then move to populations, communities, ecosystems, and biomes. Even single celled organisms participate in these levels of organization. How about zombies?

Growth and development – Living organisms increase in size and mass over their life cycle. This may be subtle, like budding yeast producing small offspring that then grow to become the same size as their parent.

Growth can take the form of hypertrophy, where existing cell(s) become bigger, or hyperplasia, where existing cells divide to become more cells. I leave it to you to decide which one occurs in single-celled organisms.

Growth and development includes the increase in cell number
as an organism grows. But cell division isn’t uncontrolled. You go
from 1 cell to about 75 trillion, but there is also a lot of cell
death. In the fetal state, if division was not accompanied by a
whole lot of apoptosis (programmed cell death), a human
newborn would weigh over a ton!
In multicellular organisms, both forms can occur. For instance, your muscles hypertrophy, while your prostate undergoes hyperplasia. Really, most instances of hyperplasia in humans is pathologic.

That doesn’t mean that increasing cell number is always bad in humans. It’s how we develop from kids to adults, how we go from a single celled zygote to an infant. Do child zombies grow up to become adult zombies? I haven’t seen enough zombie movies to render an intelligent opinion.

Energy – Living organisms acquire, store, transduce (change from one form to another) and expend energy. Acquiring energy comes in three primary forms – you gather energy from the sun (photosynthesis), from chemicals (chemosynthesis), or from eating other living things (hetertrophy). Zombies crave the flesh of other humans, so they are heterotrophs, cannibals to be specific.

Using energy means doing work – living things do work. Cells build and breakdown molecules (metabolism) and use those molecules to do work – produce heat, move, grow, sense and respond. Zombies move, although not very quickly. How slow must you be to end up a zombie meal?

Response – Living organisms have systems in place to maintain optimal growing conditions for themselves, even as the conditions around them change. In scientific terms, we call this homeostasis (homeo = similar to, and stasis = stand still).

Remember in National Treasure when Jon Voight said, “maintain the status quo.” That’s homeostasis in a nutshell. However, the processes to accomplish this can be quite complex. Just think about how many things must happen for you to try and stay cool in the heat or stay warm in the cold. Shivering alone is a very complex process of mini-spasms in your muscles.

Maintaining your blood glucose is one form of homeostasis.
Using energy lowers blood glucose, eating raises it, but you
need it to be steady. Hormones like glucagon raise the levels of
glucose in the blood, while insulin lowers it. Grehlin and
somataostatin work on your hunger and all these work through
several different cell types in your digestive tract; alpha, beta,
delta, and epsilon cells are all involved.
A new study has begun to study how your body weight is maintained whether you take in too many calories or too few. Your set point weight will be maintained until too much change has occurred over time and a new set point is established. This study found that many organs are involved, and are controlled by the brain in the effort to maintain a weight even when too much energy has been taken in. This neuronal pathway may be a new way to manipulate weight gain and loss.

Reproduction – Reproduction could mean a couple of different things. It could refer to the replication of DNA in each cell, with the passing on of hereditary material to each of the daughter cells.

In some organisms, replication and reproduction (budding or binary fission) occur together. This is most often asexual reproduction, but yeast are single-celled organisms that can exchange some DNA in a sexual mode and then divide to produce two offspring.

Do you think zombie cells replicate and form two daughter cells? If so they do a lousy job of it. Zombies looked so decayed and lose so much tissue that I find it hard to believe that they are replacing lost cells by mitosis. How about reproduction as defined by producing more versions of the parent?

For many organisms, sexual reproduction is how they produce more individuals of their species. Sexual reproduction requires replication by mitosis in all cells of the organism, as well as meiosis to produce gamete cells (sperms and ovum). I don’t know if zombies undergo sexual reproduction – and I’m not going to ask.

Zombie production is more like bacterial conjugation than
like reproduction. One bacterium possesses a characteristic
coded for by DNA. It joins with another bacterium and
transfers a copy of the different characteristic. Now both
bacterium possess that trait. Sounds like one zombie biting a
person and creating another zombie from them, doesn’t it.
In the infectious disease form of zombies, where the dead body is reanimated by the bacteria, virus, or parasite growing within them, they make more zombies by biting someone and passing on the infection. And they bite two friends, and they bite two friends, and so on…. The population grows geometrically.

This is definitely production, but does it qualify under the definition of biologic reproduction? Aren't you more changing an existing organism than producing a new one? I think this is more about conjugation rather than reproduction (see picture).

Adaptation – This means evolution. Nothing stays the same in nature. Even organisms that have been around for millions of years, like crocodiles and cockroaches, are always changing. Changing environments, fluctuating numbers of predators, etc. are constantly putting pressure on organisms. Mutations occur with or without changes around the organism, but pressures make some of the mutations positive changes and some negative changes. Those mutations that lead to more offspring and more surviving offspring are kept – natural selection, and over time there are many of these adaptations – evolution.

Remember, individuals do not evolve, only populations. So you couldn’t see a zombie evolve, even if you chose to stick around to watch – bad idea. But do zombies as a species evolve?

So how do zombies stack according to our seven characteristics? Are they an exception or a borderline case? How about other things – viruses, for instance. This is a common example for arguing about what life is. How about flame? That’s an interesting discussion to have.

Next week, some aspects of zombies involve free will - do you think they want to eat brains? Are there other examples in nature where something can steal your free will?

TedEd video (2013). The Wacky History of the Cell Theory TED

Campos M, & Jacobs-Wagner C (2013). Cellular organization of the transfer of genetic information. Current opinion in microbiology, 16 (2), 171-6 PMID: 23395479

Yamada T, Tsukita S, & Katagiri H (2013). Identification of a novel interorgan mechanism favoring energy storage in overnutrition. Adipocyte, 2 (4), 281-4 PMID: 24052907

For more information or classroom activities, see:

Immortal jellyfish –

Characteristics of life –

Wednesday, October 16, 2013

Post of the Living Dead

Biology concepts – ethnobotany, pathophysiology of diseases, zombies?

You know you have a phenomenon when you can knit a
zombie. These you can take apart and reassemble, just
like real zombies. Knitting a zombie somehow weakens
the argument that we use them to address our deep
seeded fears; these might show up at a baby shower.
Are there movies made these days that don’t have zombies in them? How did I miss the zombie aspect when I studied Lincoln and the Civil War? University classes have been developed to discuss the social implications of zombie life and why they have become so prevalent in our media.

Some “experts” believe that zombies hold fascination for us because of our need to address fears without directly confronting them. Death, the breakdown of social order, chaos, perhaps science run amok – these are all found in the zombie stories.

In fact, it could be proposed that all these fears stem from the need for expected outcomes and a sense of finality. After you die, who cares about control, order, or even diet – but what if you were condemned to be undead? What if everyone else was undead and you had to deal with their lack of finality? We watch zombie movies to deal with our own fears on a subconscious level.

Did you know that zombie legends may have some basis in truth? In the early 1980’s an ethnobotanist from Harvard named Wade Davis claimed to have found two potions used to create zombies.

In Haiti, the fear of zombies has been present for many years. Based in African folklore and maintained by the descendents of slaves that revolted and remained in Haiti, witch doctors (bokurs) are very real sources of reverence and fear for the average man and woman. Just how the bokors managed to create zombies was the question asked by Dr. Davis.

Ethnobotanists are scientists that study different
civilizations (ethno-) for how they use plants (-botanist)
in medicine and culture. Mark Plotkin spent years with
tribes in the Amazon studying the use plants by the
medicine men. After returning with many plants from
which to extract compounds, Plotkin started Shaman
Pharmaceuticals to test the compounds for medicinal uses.
Plotkin now runs an Amazon Preservation organization.

Davis claimed to have found a powdered potion that could make a person appear to be dead. Based on a toxin called tetrodotoxin, Davis said the powders were most commonly blown into the faces of victims and the toxin would inhibit firing of voltage-gated channels in the nerves. Heart rates would go to near zero and the affected individuals would seem dead.

In many cases, tetrodotoxin doesn’t just make people appear dead, it kills them for real. Blue ringed octopods, several species of fish, and other animals contain this toxin and it will mostly certainly kill. The sushi dish called fugu is a pufferfish that contains tetrodotoxin. Even when prepared correctly (which takes a government issued license), the consumer will experience numbness in their tongue and mouth. Davis stated that dosing the victim often resulted in real death; making zombies is apparently not so easy.

After a hasty burial, the bokor would dig up the poisoned victim before true death occurred, and a zombie slave was produced by giving a second potion. This poison was based on a Jimson weed (Datura stramonium) extract, leading to the second name for the plant, zombie cucumber.

Jimson weed extract is a psychoactive agent that leads to stupor and amnesia, but no loss of consciousness. There said to be the basis of the loss of free will, and slow dragging movements of zombies. In such a state, the affected could be turned into slave labor, or used to frighten others into compliance with the bokurs’ wishes.

Davis’ samples and explanations were not accepted by the majority of the scientific community. The toxins described are very toxic; small mistakes in dosage would most certainly be fatal. And a motive of creating cheap labor is not convincing; most labor in Haiti is cheap.

But don’t try to tell that to the Haitians. They actually have a law forbidding the creation of zombies. Article 249 of the code of laws states, “It shall also be qualified as attempted murder the employment which may be made against any person of substances which, without causing actual death, produce a lethargic coma more or less prolonged.” Scary.

So let’s talk zombies. Some people will get into intricate detail, but let’s confine ourselves to two kinds of zombies. One kind of zombie was dead but is now reanimated by some means – usually some kind of parasite or virus that brings some tissue back to life. The other sort of zombie always remains living, but loses all ability to direct its own thoughts and actions; it is driven only to acquire flesh – usually bbrraains!

The top cartoon shows how the valves in your veins work to
keep blood from pooling in the lower extremities. For veins
above your heart, you don’t need the valves, so they don’t
have them. On the bottom, you can see what happens in the
case of varicose veins, when blood will begin to pool. The
picture on the bottom right shows what happens when
valves go bad (insufficiency). Can you get varicose veins
above your heart – yes, but it usually requires
severe liver damage.
As a biologist, the undead zombie troubles me for several reasons. No heartbeat, little brain activity – just what is moving them and how do they digest the brains they eat? I know that some sites have very intricate back stories as to how they stay upright and mobile, but they don’t hold water scientifically.

If they have no heartbeat, how do they circulate their blood? I saw one website that stated unequivocally that muscle movement (contractions and relaxation) pushes the blood around the body. Ridiculous, right? Not really. You do this every minute of every day. On the artery side of our circulation, the muscle in our vessels work with the contraction of the heart to push the blood along, but across the capillary bed, there is little pressure left to push blood through the veins.

So you use the action of your large muscle groups to squeeze the blood in the veins. When you walk, bicycle, or step dance, the contractions push the blood up against gravity. Your veins have one-way valves, so after the blood passes a valve, it won’t flow backwards. If this wasn’t so, all your blood would end up in your feet, and you’d have to buy shoes like Shaquille O’Neal’s.

On the other hand, if we are talking about living dead zombies, then there are many possible biologic causes. Rabies is caused by a bacteria passed through the bite of an infected animal. The result is an infection that can take one of two forms. In furious rabies, the victim will display erratic behavior, aggressiveness, foaming at the mouth, and will eventually start biting people.

The paralytic form of rabies will cause slow movements, dragging feet, lack of coherent behavior, and foaming at the mouth. The foaming is due to the inflammation of the throat that makes it so painful to swallow that victims will choose to drool and foam instead. Either form of rabies could mimic what we think of as zombies.

The top picture is Cujo, from the Stephen King story of the
same name. The dog was huge, and then caught rabies from
a little field animal. He lost all sense of personal hygiene and
liked to bite anything that moved – just like zombies. Below is
a photomicrograph of the negri (named for Adelchi Negri)
bodies that appear in the brain tissue of rabies victims. They
stain darkly and are made up of riboproteins made by the
rabies virus.

Most people believe that you get bit, and then you develop rabies, so it is easy to put cause with effect. But a new study shows that rabies can incubate for decades before symptoms manifest. The man in question showed signs while he lived in the U.S., but the organism he harbored is found only in Brazil, a place he hadn’t lived or visited for many years, although he did remember a biting incident in his home country. If the symptoms occur out of nowhere, does that support or negate the idea that he might be a zombie?

If you want an example of living dead, look no further than African sleeping sickness (also called trypanosomiasis). The bite of the tsetse fly transmits the Trypanosoma brucei parasite, which then takes up residence in brain.

The symptoms get progressively worse, starting with headaches and moving through slurred speech and then to a zombie like state with sleep being impossible at night and staying awake being difficult during the day. They enter a living nightmare, unable to respond or act, until they fall into a coma and die after a few weeks. Sounds like a zombie to me.

African sleeping sickness is an often fatal disease with parasites
invading the brain and doing damage. Survivors are usually
permanently brain damaged. The tsetse fly (below) is the vector
that carries the trypanosome. While it takes a blood meal, it
vomits the organisms into the wound
Current estimates are that nearly 200,000 people are infected with T. brucei, although new cases are dropping significantly – yea. This a significant disease that requires diligent public health measures to keep the number of flies under control and to protect the population from the flies. It was once thought that humans had to move into the woodland to meet up with the tsetse flies, but new studies show that the flies do enter buildings.

Recently, a study showed that things thought to be repellent to tsetse flies, such as smoke or human presence in a confined space, did not stop the flies from alighting on humans inside buildings. The number of landings also increased as the temperature increased. Buildings must now be considered a possible venue for disease transmission. But at least with this disease you can just go to sleep, it isn’t like your ear will fall off.

Leprosy (Hansen’s disease), on the other hand, can present some of the bizarre symptoms seen in zombies. The causative organism is Mycobacterium leporae, and has been around for thousands of years. There was no treatment for most of those years; an effective antibiotic regimen was not devise until the 1940’s. Because of this, leper colonies were used for two thousand years to separate the victims from the rest of the population. This is interesting, because it’s relatively hard to catch Hansen’s disease.

On the left is a leprosy victim. Remember that leprosy itself
doesn’t cause loss of body parts, but secondary infections are.
The 9 banded armadillo is one of the very few animals that is
susceptible to leprosy, so it is often used in the laboratory. Below
on the right, current treatments are very effective at alleviating
the swelling and skin lesions associated with the disease. Leprosy
shouldn’t be considered a killing or disfiguring disease anymore.

The disease has a very long course because it is a very slow growing bacterium; the doubling time is about 14 days. M. leprae has a predilection for setting up shop in skin and nervous tissue, and this is the reason it is linked to zombies. Leprosy itself doesn’t cause body parts to fall off, but it does compromise the blood flow and immune reaction in extremities.

Secondary infections can then gain a foot-hold and cause loss of fingers and such. This tendency for loss of noses, ears, etc. is exacerbated because the organism prefers it a bit cooler, so it tends toward areas with lots of surface area and less blood flow. A new study shows that M. leprae causes damage to the olfactory bulb, affecting the size of the nervous tissue responsible for smell sense. This would be especially bad for zombies, since they are said to act mostly on a sense of smell to attract them to potential victims.

The damage to skin and nerves could additionally contribute to a look of decay about the face and body, and a shuffling gait – also zombie like properties. Even zombies don’t want to catch leprosy.

Next week, can we use rigorous biological analysis to determine if zombies are a form of life? I sure hope so, or it’ll be a short post.

Boland TA, McGuone D, Jindal J, Rocha M, Cumming M, Rupprecht CE, Barbosa TF, de Novaes Oliveira R, Chu CJ, Cole AJ, Kotait I, Kuzmina NA, Yager PA, Kuzmin IV, Hedley-Whyte ET, Brown CM, & Rosenthal ES (2013). Phylogenetic and epidemiologic evidence of multi-year incubation in human rabies. Annals of neurology PMID: 24038455

Vale GA, Hargrove JW, Chamisa A, Hall DR, Mangwiro C, & Torr SJ (2013). Factors affecting the propensity of tsetse flies to enter houses and attack humans inside: increased risk of sleeping sickness in warmer climates. PLoS neglected tropical diseases, 7 (4) PMID: 23638209

Veyseller B, Aksoy F, Yildirim YS, Açikalin RM, Gürbüz D, & Ozturan O (2012). Olfactory dysfunction and olfactory bulb volume reduction in patients with leprosy. Indian journal of otolaryngology and head and neck surgery : official publication of the Association of Otolaryngologists of India, 64 (3), 261-5 PMID: 23998032

For more information or classroom activities, see:

Ethnobotany –

Vein valves –

Rabies –

African trypanosomiasis –

Hansen’s disease –