Canine epilepsy is a brain
disorder that is manifested in the form of recurrent seizures, and is the most
common chronic neurological disorder seen in dogs. The majority of dogs being
diagnosed with idiopathic epilepsy, which is often described as having no underlying
cause, though it is thought to have a genetic basis, are diagnosed between the
age of 3 and 5 (Chandler 2011). Nearly
all breeds of dogs have recorded incidents of idiopathic epilepsy and when we
compare them with other domestic animals, the dog has the highest incidence of
epilepsy, ranging from 0.5% to 4.1% dependent on breed. Seizures that occurred
before or after this age range are more likely to be caused by infection,
trauma, a metabolic disorder, or some other measurable disease process (Oberbauer, Grossman, Irion, Schaffer, Eggelston
& Famula 2002).
The University of Prince Edward Island (UPEI)
(2014) have compiled a database of canine inherited disorders, in which they
cite idiopathic epilepsy as a genetic disorder, and while the exact genetic
make-up of this disorder is largely unknown, they suggest that more than one
gene is involved. This is supported by Oberbauer et al (2002) who state that ‘there
is a growing body of evidence that supports a hereditary basis for idiopathic
epilepsy in the dog’, and by Rusbridge (2014) who describes a late
onset form of epilepsy called Lafora’s disease (usually occuring in animals
over seven years of age), which is found in the Miniature Wire-Haired
Dachshund, Basset hound and Beagle, and suggests this disease is caused by an
autosomal recessive inheritance, in which both parents will either carry or
have the disease, with the Beagle showing a more severe form of the disease.
It is important to rule out
one-off causes of a seizure such as heatstroke (which is not uncommon in
puppies, just as febrile convulsions occur in humans), as a one-off episode of
seizure shouldn’t be used as an indicator of a serious breed-related problem. In
March 2014, the UK Kennel Club approved a DNA
Lafora test which has been developed in Canada and the
results are held in the Kennel Club database, through the dog’s registration
details, and then published in the club’s breed supplement; through this
process the Club states it aims that ‘responsible
breeders can safely use all dogs not suffering from this condition, to eliminate
this condition over time, to protect the diversity of the breed, without
producing affected dogs’, but they do note that this is
only a recommended test, and that the aim is only as good as the information
they receive from responsible breeders (The Kennel Club 2014)
Veterinarians
rely heavily on the accounts of owners to reach their diagnosis, some of which
may not know their dog has had a seizure, because while a major seizure that
has the dog paddling on the ground with complete loss of motor control is easily
comprehended, a minor seizure may appear as a slight loss of muscle control, or
even just a loss of attention (called an absence); and often the episode is
over by the time the vet is called, so the use of video is often recommended to
confirm epilepsy and drive the correct treatment regime (Hahn 1997).
The
first line of treatment for canine epilepsy is the use of barbiturates, such as
phenobarbital, or potassium bromide (Compass 2014), both of which work to inhibit
the nerve impulses (although by differing mechanisms). Munana (2009) suggests
that only about 20 -30% of dogs achieve a good level of control without serious
side effects, mainly sedation and vomiting, so often owners will reduce or stop
medication to negate the side effects. Conversely owners may seek out excess
medication, by exploiting the fact that Veterinarians rely on owner reporting
of suspected seizures.
Dryden-Edwards
(2014) suggests that a rise in the use of stimulating drugs, such as cocaine,
and methamphetamine, has seen an increase use of barbiturates (downers) to
counteract the ‘excitement’ phase of drug abuse, when the user needs to appear
‘normal’ with the resulting need to continue as the
brain develops a dependence on the barbiturate, which causes withdrawal
symptoms when the drug is withheld
Fremuth
(2003), suggests, in her article for the Australian Shepherd Journal, that many of the above mentioned factors
come into play when breeders are faced with a breeding dog with idiopathic
epilepsy, she suggests that many breeders will not openly discuss if there is
epilepsy in their breed and particularly in their stud, for fear of losing
their status; also that just the suspicion of epilepsy in a breed can impact a
breeder even if none of their dogs are affected; so the pressure to keep any
hint of epilepsy ‘confidential’ is overwhelming.
Fermuth proposes the reasons that breeders would ‘hide’ whether their
dog or dogs had epilepsy has many facets, the knowledge of seizures puts the
breeder in a catch 22 position, if they mention seizures, to try to improve the
line, then there is a reduction in the price they can achieve, but if they
don’t mention it then they open themselves up to possible litigation. The fact
that most idiopathic epilepsy begins in adulthood means that puppies are sold
without any indication of whether they have the disease, and allows breeders to
state ‘they had no idea’ when challenged. With the attitude that many breeders prefer
not to know about epilepsy in their lines, it is difficult to make informed
choices about appropriate matings.
Budiansky (1999) suggests that one reason for the rise in inheritable
diseases (which may or may not include idiopathic epilepsy) is that many breeds
suffer from the ‘popular sire effect’ in that a successful champions is in
great demand, commands high stud fees, and is likely to sire hundreds of
litter, potentially swamping the gene pool with defective genes, often breeding
out healthier ancestral lines.
Responsible breeders should be screening for inherited disorders,
because it is the responsible thing to do, and it could be argued that these
breeders will eventually be rewarded by producing health individuals that will
command even higher prices, but there would need to be a change of emphasis
from one of secrecy to one of openness, by making official test results public
record, in order to reduce the production of epileptic individuals (Bell 2014).
References
Chandler, K. (2011), treatment
and monitoring of epilepsy in dogs, In Practice 2011;33:98-104
Compass (2014), [course
notes], Module 4 Pharmacology.
