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Hydrocephalus In Syrian Hamsters

Although hamsters with water on the brain have adorable looks, the ailment will likely shorten their life.

Leticia Materi, PhD, DVM
Posted: December 1, 2015, 5:10 p.m. EST

two photos of a hamster
Courtesy of Margaret Chu  
A dome shape to the forehead and more bulging eyes are signs of hydrocephalus.

People use many factors to choose a pet. One is appearance. While most people say that good health is important, many also want cute pets. So what exactly does a "cute” pet look like? Studies done in the 1970s by Konrad Lorenz suggest that humans prefer images of animals with smaller snouts, higher foreheads and larger eyes. Essentially, we prefer characteristics associated with babies or juveniles. The tendency for people to choose pets with these traits has likely influenced breeding programs.

A perfect example of this is the Holland Lop rabbit. Breed standards for these animals include an arched or curved crown of the head and short muzzle. These characteristics make Holland Lop rabbits adorable. However, there is a negative side to breeding these types of physical traits. What is often forgotten is that external features often have huge implications for internal structures. By selectively breeding for shortened faces, Holland Lops are much more prone to dental disease because the size and number of teeth have not changed, but the length of the jaw and face has shortened. Thus, the teeth are forced into a smaller area, which some people believe leads to malocclusion.

Another animal that seems to have a genetically linked medical disorder related to appearance is the Syrian hamster. The disease of concern is hydrocephalus.

two photos of a hamster
Courtesy of Wendy Abrahamson
Currently there is no cure for hydrocephalus in hamsters. If clinical signs are mild, a hamster could live a relatively normal life with special care.

Hydrocephalus is a condition in which excess fluid, specifically cerebrospinal fluid (CSF), accumulates within the brain. Normally, there is fluid produced within spaces of the brain known as the ventricles. The CSF flows from the ventricles and around the brain to cushion it, distribute nutrients and remove waste products. In healthy bodies, the production of CSF is balanced by its reabsorption into the bloodstream. 

While hydrocephalus can develop due to the presence of certain infections or toxins, in hamsters most cases appear to be hereditary. When fluid builds up in the ventricles, it begins to put outward pressure on the surrounding brain tissue. This leads to neurological signs, such as seizures, lethargy, poor coordination, head pressing and visual impairment. In young animals, before the bones of the skull have fused, the expanding brain forces the skull to expand — leading to a high forehead and domed skull. Anecdotally, there have been reports by a few hamster breeders that some hamsters with hydrocephalus also have poor teeth development, but further studies are necessary to examine the extent of this correlation.

While this condition has been mostly studied in laboratory animals, it has been suspected to also occur in the pet hamster population. The prevalence of the disorder in the pet population is unknown, as postmortem analysis of brain tissue from pet hamsters is rarely performed. In the laboratory setting, the condition is considered widespread and the severity of the disease varies significantly. Sometimes the disease is so severe that the affected animals do not live very long. However, one study demonstrated that many hamsters with hydrocephalus can live longer than expected. Even hamsters that appeared physically normal could produce offspring with hydrocephalus, suggesting that this condition is a recessive genetic trait. Interestingly, none of the wild-caught hamsters that were studied demonstrated any signs of hydrocephalus.

In humans, hydrocephalus is treated with surgically placed shunts to help drain fluid from the ventricles of the brain. To date, this is not possible in hamsters. At best, mild clinical signs may be managed with steroids and anti-seizure medication. However, euthanasia is the only humane option for those animals with uncontrolled clinical signs. 

Conditions such as these underscore the need for selective breeding programs. While we may desire certain physical traits in our pets, I believe that it should never be at the expense of good health.

Note: All articles by Dr. Materi are meant for educational purposes only and in no way represent any particular individual or case. They are not for diagnostic purposes. If your pet is sick, please take him or her to a veterinarian.

Posted: December 1, 2015, 5:10 p.m. EST

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