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What is WHS?
There are many places where you can read on the Internet that WHS (Wobbly Hedgehog Syndrome) is a genetic disorder, and is even attributed to a simple recessive gene pattern. This is touted as fact, but the real truth is that there’s a whole lot more to the story and that this is NOT a fact.
To begin any discussion, first it’s important to discuss what exactly a term means. Sometimes WHS is used to describe any hedgehog that is wobbling. This can mean any number of things and does not necessarily mean that the animal has Wobbly Hedgehog Syndrome. To determine if a hedgehog has WHS, a necropsy is required. Apparently, the hallmark of WHS is a particular type of brain lesion. Most necropsy reports state simply that a hedgehog has “WHS lesions.” So, what does this mean? In an email Donnasue Graesser sent my mother, she identified these lesions specifically as “multifocal luekoencephalopathy.” So, if your vet says that your hedgehog died of WHS, the first thing you need to establish is whether they are just describing the fact that your hedgehog had a wobbly gait or whether it actually had lesions consistent with multifocal leukoencephalopthy identified.
Turning to the literature, the Merck Manual, which pertains to humans, states:
“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. On his web page at http://www.virology.ed.ac.uk/research/Fazakerley.htm, Dr. John Fazakerly, a pathologist, includes multifocal leukoencephalopathy as one of the CNS 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, progressive multifocal 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 neurone 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 on the matter when a hedgehog that I bred was reported to have had been found to have multifocal leukencephalopathy lesions when necropsied. The hedgehog also had cancer. He told me that there was no reason to believe that this was inherited, particularly given the lack of other instances in a fairly extensive family tree, and that it would be premature 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’s highly unlikely that it’s genetics at play. Several of my friends also asked their veterinarians and received similar responses.
In order to obtain further information, I decided to try to contact a veterinarian who had no ties to me, 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 wasn’t there on the day that I called, but I did speak 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, and asked five specific questions about WHS, and ask that they send a response that I be allowed to publish on my website any response that I received 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 WHS 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.
3) "WHS 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 the same infectious disease or even eat a similar diet.
I will try to find out more. It's apparent you see the distinction between anecdote and real science.
Angela M. Lennox, DVM, Dipl. ABVP-Avian
President: Association of Exotic Mammal Veterinarians”
It seems fair to conclude that at this point, there is a whole lot more that we do not know than that we do know about WHS.
It appears that far more research is needed before any conclusions can be drawn about what causes WHS. It also appears
clear that it is not accurate to concluded that if a hedgehog is found to have “WHS lesions” when necropsied, that it is a
carrier of a genetic problem, and that experts do not uniformly recommend that any animal whose offspring is found to have
"WHS lesions" should be retired from breeding. 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.
It is very important that, as we try to learn more about WHS, we look at the big picture. 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 therefore allow a virus to flourish. Rather than just comparing
animals that have “WHS lesions” and animals that do not, it would then also be 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 in
this manner 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. At this point, WHS is not necessarily considered the
cause of death in many hedgehogs that are found to have "WHS lesions."
Thankfully, research is continuing, and as more veterinarians and pathologists share information, we will understand more
about what is going on. I hope that you will continue to ask questions and consult any veterinarian and researcher that you
know, because the more minds that work together, the more likely we will truly be able to help our hedgehogs.
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