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What is Wobbly Hedgehog Syndrome (WHS)?
Many hedgehog owners and breeders are very concerned about a scary
illness called Wobbly hedgehog Syndrome, or WHS for short. You can find
many articles on the Internet that tell you about how it is a genetic
disorder. It is a widespread belief that WHS is caused by a simple
recessive gene pattern. Breeders state on their websites that their
hedgehogs are "WHS free" and that they guarantee babies from their herd
will never get WHS.
The truth is that there
is a whole lot more to the story.
How is WHS defined?
Before getting into more details, it is important to step back and
define Wobbly Hedgehog Syndrome (WHS). Sometimes the term WHS is used to describe any hedgehog that is wobbling.
Wobbling can mean any number of things and does not always mean that the
hedgehog has Wobbly Hedgehog Syndrome.
Only a necropsy can determine if a hedgehog has WHS. This is because the hallmark of WHS is a particular type of brain lesion. Most necropsy reports
just state that a hedgehog has "WHS lesions." So, what does that mean?
In an email
that pathologist Donnasue Graesser (who has studied WHS) sent my mother
(a retired histochemist), Donnasue identified these lesions specifically as
So, if your vet says that your hedgehog died of WHS, you need to find
out is whether the vet is just describing the fact that your hedgehog
looked wobbly or whether it actually had multifocal leukoencephalopthy
type lesions identified.
What does it mean if my hedgehog had these
Turning to the literature, the Merck Manual
states that in humans "Progressive multifocal leukoencephalopathy
results from infection by the JC virus. The disorder affects mainly people whose immune system is impaired, such as people who have leukemia, lymphoma, or AIDS, or is suppressed by use of immunosuppressants, which may be used to prevent rejection of transplanted organs or to treat autoimmune disorders."
Wikipedia offers this definition:
"Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of the central nervous system
caused by reactivation of a latent papovavirus (the JC virus) infection. It affects immune-compromised patients and is usually seen with patients having AIDS."
Veterinary neuropathology textbooks offer similar definitions
with regard to other species of animals. Dr. John Fazakerly, a pathologist, includes multifocal leukoencephalopathy as one of the
central nervous system diseases for which a viral vector is being investigated:
"Many important diseases of the CNS are caused by virus infections, these include, poliomyelitis, HIV dementia, subacute sclerosing panencephalitis, progressivemultifocal leukoencephalopathy, tropical spastic paraparesis, rabies, distemper, visna and numerous encephalitides such as Japanese or California encephalitis. In addition, there are numerous diseases ranging from motor neuron disease and multiple sclerosis to various neuropsychiatric and Parkinsonian diseases which have been suggested, with variable justification and in at least some cases, to have a viral aetiology."
I asked my veterinarian , Dr. Darrell Monfort, for his thoughts
about the cause of WHS when a hedgehog that I bred was reported to have had been found to have multifocal leukencephalopathy lesions when necropsied. That hedgehog also had cancer.
Dr. Monfort told me that there was no reason to believe that this was inherited,
since there were no other instances of WHS in a fairly extensive family tree.
If WHS were a simple recessive trait, we would see many, many cases. He
indicated that it would be too early to conclude that this was a genetic disorder without more information.
I also asked a friend of mine who is a very experienced veterinary pathologist, who told me that given what she knows about multifocal leukoencephalopathy in general, it
is highly unlikely that it involves genetics.
Several of my friends also asked their veterinarians and received similar responses.
In order to obtain further information, I decided to contact a veterinarian who had no ties to me
or anyone I know, either personally or professionally.
Because of the article about hedgehogs that he wrote for the October 1999 edition of Veterinary Medicine magazine and because he is recognized by other veterinarians as being knowledgeable about hedgehogs, I thought it would be appropriate to call the veterinary clinic at Kansas State University to see if I could speak with Dr. Carpenter.
Dr. Carpenter was not there on the day that I called,
so I spoke with Dr. Pollock, who stated that they would staff my inquiry and route some questions that I had to the person they felt would be best able to give an answer. I referred Dr. Pollock to wobblyhedgehog.org and to the Hedgehog Breeder's Association newsletter as references to WHS being allegedly genetic.
Then, I asked five specific questions about WHS. I requested that they send a response that I be allowed to publish on my website to help others better understand what is and is not known about WHS at this point.
About two weeks later I received an email from Dr. Angela Lennox, President of the Exotic Animal Veterinarian's Association. Her email read as follows:
Dr. Pollock asked me to try and answer some of your questions regarding Wobbly Hedgehog Syndrome. I am the current president of the Association of Exotic Mammal Veterinarians. Much of the work done on this syndrome is being done by Dr. Michael Garner, an exotic animal pathologist. He has about 30 documented cases, and is working on finding the etiology.
Possible causes include a virus or bacteria, or other infectious agent, a nutritional cause, or a genetic cause. According to Dr. Garner there is not enough evidence to know for certain.
I will follow up with Donnasue from the HWS and Dr. Terry Spraker to see what evidence they might have that there is a genetic component. I don't see that this has been proven, either.
As you know, sometimes a simple statement becomes repeated over and over and then becomes fact.
1) If my hedgehog has a "wobbly" walk and my vet says it probably has Wobbly Hedgehog Syndrome, what does that mean? WHS should be considered in the list of possible diagnoses, along with spinal cord injury, and general overall weakness from
other medical conditions.
2) If my hedgehog dies and the necropsy report says that it has "WHS lesions," does that mean it has a genetically inherited disorder
? Are there any other questions I should ask the vet who did the necropsy?
Not according to what I know so far.
lesions" have been referred to as multifocal leukoencephalopathy. Is it
a fact that multifocal leukoencephalopathy is inherited from a recessive
gene, or are there other equally or more likely possibilities? What evidence is there that there
might be other causes?
According to Dr. Garner we have to consider infectious (virus, parasite, bacteria), and nutritional in addition to genetic.
4) A number of people have indicated that there is "proof" that Wobbly Hedgehog Syndrome is genetic. Is there anything
published to support this, or any other theories about it, in peer reviewed literature?
Nothing published and nothing in the literature. Dr. Garner will publish his findings this year, and as of right now he is not
sure of the etiology. Perhaps another researcher knows more and will publish these findings soon.
5) If a hedgehog someone bred is diagnosed with multifocal leukoencephalopathy ("WHS lesions") and cancer, should they
automatically remove all of its relatives from their breeding program? Or, is there other information that should be
utilized to make this decision?
It would certainly be interesting to look for higher incidence in certain family lines. However, we can't confuse this with
the fact that related hedgehogs may simply have been exposed to the same infectious disease or even eat a similar diet.
I will try to find out more. It is apparent you see the distinction between anecdote and real science.
Angela M. Lennox, DVM, Dipl. ABVP-Avian
President: Association of Exotic Mammal Veterinarians"
What does all
means that there is a whole lot that we do not know about WHS.
More research is needed before any conclusions can be drawn about what causes WHS. It appears
clear that it is not accurate to conclud that if a hedgehog is found to have "WHS lesions" when necropsied, that it is a
carrier of a genetic problem. Experts do not uniformly recommend that any animal whose offspring is found to have
"WHS lesions" should be retired from breeding. It means that people cannot
guarantee that their animals are WHS free because we don't know enough
about it to be able to make that statement. It means that WHS is
likely not genetic or that genetics only plays a very small role.
How do we learn more?
Just because two things are correlated, does not mean that one is the cause
of the other (ie: correlation is not causation). For example, just because the highest rates of ice cream sales occur at the same time that
the highest rates of shark attacks are reported and the lowest rates of ice cream sales occur at the same time that the lowest
rates of shark attacks occur, it is not a fact that ice cream sales cause shark attacks or vice versa.
We should be careful of assuming that we know things just because two
things occur together and we need to look for bigger patterns, if there
For example, one theory is that WHS
is caused by a virus, similar to what is known to cause multifocal leukoencephalopathy in humans. One way of looking at this
theory is to look at whether or not hedgehogs that are found to have lesions consistent with multifocal leukoencephalopathy
also have problems that would weaken the immune system and allow a virus to flourish.
Rather than just comparing
animals that have "WHS lesions" and animals that do not, it is important to examine the difference in
populations that have A) no lesions B) potentially immunosuppressive problems and no WHS lesions C) WHS lesions and
no immunosuppressive problems and D) WHS lesions and potentially immunosuppressive problems. Looking at the data
this way may lead to new conclusions that cannot be found if the categories are artificially limited and potential intervening
variables or alternate explanations are ignored.
It is also important to look at the incidence in a large, randomly selected
population in general. This would help clarify things such as whether a hedgehog's death is caused by the WHS or whether
the WHS was caused by the illness that the hedgehog had developed. In many of
the hedgehogs that have been studied, WHS is not necessarily considered the
cause of death in many hedgehogs that are found to have "WHS lesions."
Another way to help learn more about WHS would be to identify a hedgehog
that has exhibited the multifocal leukoencephalopathy and track multiple
generations. Completing a necropsy all of the hedgehog in that line,
once they pass, to check for lesions and immunosuppressive disease would
assist in identifying whether the incidence is greater than chance in a
As more veterinarians and pathologists share information
and more hedgehog owners insist on looking beyond, we will come to understand more
about WHS. Please continue to ask questions and consult any veterinarian
or researcher that you
know. The more minds that work together to question assumptions and study with
good scientific method, the more likely we will truly be able to
understand and help our hedgehogs.
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Last updated by Tig