|
What
is congenital deafness and vestibular disease?
http://www.upei.ca/cidd
related terms: congenital peripheral vestibular disease |
The vestibule is an oval
cavity in the inner ear containing tiny bones (bony labyrinth) and
sensory cells that affect locomotion and are part of the hearing
system. In dogs with this condition, some of these structures begin to
degenerate shortly after birth. Affected dogs show early signs of a
vestibular deficit (eg. a head tilt, lack of coordination, and
circling) and become completely deaf by about 3 weeks of age, although
this is often not noticed until later.
How is congenital deafness and vestibular disease inherited?
This disorder has been most studied in the Doberman pinscher, in which
it is believed to be an autosomal recessive trait.
What breeds are affected by congenital deafness and vestibular
disease?
Doberman pinscher. Deafness with vestibular signs is
also reported in the beagle, Akita, English cocker spaniel, German
shepherd dog, Shetland sheepdog, and Tibetan terrier.
For many breeds and many disorders, the studies to determine the mode
of inheritance or the frequency in the breed have not been carried out,
or are inconclusive. We have listed breeds for which there is a
consensus among those investigating in this field and among veterinary
practitioners, that the condition is significant in this breed.
What does congenital deafness and vestibular disease mean to your
dog & you?
Although affected puppies are lively and alert, owners or breeders will
usually see signs such as a head tilt, circling behaviour, or a
tendency to roll over or fall by 10 to 16 weeks of age. Pups lose their
hearing a few to several weeks after birth. Signs of bilateral deafness
may include aggressive play because the deaf pup does not hear cries of
pain from littermates, and having to be jostled to waken.
The clinical signs such as circling, head tilt, and lack
of coordination usually improve with age. This is a result of
compensation by other parts of the brain. However specific tests show
that the underlying vestibular deficit remains the same.
Deafness is permanent. Although dogs can accommodate remarkably well in
familiar surroundings, dogs that are deaf in both ears startle easily,
are difficult to train, and are prone to accidents. For these reasons,
they are usually euthanized as pups if the condition is recognized
early. As an alternative, an owner may train the dog to respond to hand
signals or other visual cues, always restrain him/her on a leash or in
a fenced yard, and be alert to the possibility of the dog biting
someone if startled.
How is congenital deafness and vestibular disease diagnosed?
The clinical signs (head tilt, circling, etc.) point
to a vestibular deficit. Your veterinarian will do blood tests to
rule out various possible causes, since this particular disorder is
fairly rare. A BAER (Brainstem Auditory-Evoked Response) test is
required to evaluate hearing, as hearing loss can be very difficult to
assess by clinical examination (ie. behavioural response to sounds).
The BAER test is a painless and reliable means of detecting hearing
loss in one or both ears, that is available at veterinary schools and
referral centres. It can be used in puppies of 5 weeks of age on. Older
pups and adult dogs may need to be sedated for the test.
How is congenital deafness and vestibular disease treated?
There is no treatment or cure. The clinical signs of a vestibular
deficit are likely to improve with age; deafness is permanent.
Breeding advice
Although little is known of the inheritance of this condition in breeds
other than the doberman, affected dogs should definitely not be bred.
It is preferable not to breed their close relatives (parents or
siblings) either.
FOR MORE
INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Resources
Wilkes, M.K., Palmer, A.C. 1992. Congenital deafness and
vestibular deficit in the doberman. J. of Small Animal Practice. 33:
218-224. This reference has detailed information on the pathological
changes seen with this disorder.
Copyright
© 1998 Canine Inherited Disorders Database. All rights reserved.Revised: October 30, 2001.
This
database is a joint initiative of the Sir James Dunn Animal Welfare
Centre at the Atlantic Veterinary College, University of Prince Edward
Island, and the Canadian Veterinary Medical Association.
reprinted with kind permission from:- Alice Crook,
DVM,Coordinator, Sir James Dunn Animal Welfare Centre, Atlantic
Veterinary College,University of Prince Edward Island, 550 University
Ave.Charlottetown, PEI C1A 4P3
http://www.upei.ca/cidd
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*******************
Dogs that cannot hear are
quite often written off as too difficult to train, unable to recall or
be let
off lead and generally unable to live a ‘normal’ life. But a deaf dog
only
has one of the five senses missing and can accommodate for this loss
much
better than you might imagine. With their heightened sense of smell and
eager eyes, a deaf dog can understand, interact and learn just as well
as
their hearing companions. With a little time and imagination from their
owners, a deaf dog can learn all the behaviours that a hearing dog can,
including
recall.
Deaf Dog Hand Signals
The key to a ‘normal’ relationship with your deaf dog is to substitute
the spoken word for some hand signals. Some people learn commands from
UK or USA sign language standards. Alternatively, you can make up your
own
signs to suit you and your dog. Have some fun and be inventive but bear
in mind that all signs should be clear, easily distinguishable from
other
signs and preferably even performed away from your body so that your
sign
is clearly visible to your dog. For this reason, by all means look up
some
official signs but do adapt them to your own needs, or change them
completely
into something that you can easily remember. We made up many signs for
our
deaf dog, Berkeley. Only a few of them are large and away from the body
such
as the recall sign. Most are more discrete as Berkeley is very
observant
and also rather frightened of large sweeping hand movements. See how
you
get on and don’t be afraid to adapt your signs to your own dog’s needs.
Using Sign Language with a Deaf Dog
Whatever signs you choose, be consistent. Make a note of the signs you
intend to use and maybe draw them out. Put them on the fridge door or
somewhere easy to view and stick to those signs.
Start to use your signs exactly as you would normally speak to a
hearing dog. Start with some everyday pleasant events such as a sign
for ‘dinner time’ and a sign for ‘walkies’. These are two activities
that most dogs
love. So, for example, get your dog’s attention with a gentle tap near
the
shoulder blades and sign for ‘dinner’ and then put the food bowl down
or
sign for ‘walkies’ and immediately get the dog lead off it’s hook. You
will
be amazed at how quickly your deaf dog will come to associate the sign
with
the event that follows. Keep using your chosen sign and watch your
dog’s
reaction. If they respond with excitement and prepare for walkies or
dinner
then you have successfully communicated to your deaf dog.
Congratulations.
You will be surprised how the rest of the signs will follow easily.
Your deaf dog soon learns that your hands and movements are telling
them interesting things.
Speak as you Sign
It is always a good idea, when signing, to also speak to your dog. If
you are signing something happy such as ‘walkies’, it helps if you are
smiling as you sign. As you sign ‘walkies’ also say ‘walkies’ and this
will show in your face. Dogs are experts at reading body language,
including facial expressions. The sign will be learnt quicker and have
more meaning to your dog. Of course, the same goes for naughty signs
such as ‘no’. Perform your sign for ‘no’ but also say ‘no’ at the same
time, which will help you to
convey your meaning.
Training a Deaf Dog with Hand Signals
Now you are in the swing of using your hand signals consistently and
for everyday activities, you can begin some basic training. Remember,
we
are training a dog, it just happens to be a deaf dog. The basic rule is
to train the same way you would train a hearing dog but add hand
signals
to your verbal commands. It is important to remember this. All the
usual
rules of good basic dog training apply*.
Training a deaf dog is not really that different to training a hearing
dog. At most it will involve a little more time and patience, but it is
possible and deafness is not ever an excuse for a poorly behaved, under
trained pooch.
Good Basic Dog Training:
Train your dog using whatever motivates them, be it a food treat or a
favourite toy. Keep training sessions short (5-10 mins per session) and
always
end training sessions on a positive note such as an easy trick that you
know
your dog can perform. Never shout or loose your temper and never train
if
you or your dog is tired or getting bored. Always use positive training
methods
as you will get much better results and your pooch will thank you for
it.
This
article is strictly copyright to D for Dog © www.dfordog.com
Any part of this
article can only be replicated or used with our express permission or
by clearly crediting D for Dog and linking to us.
********************************
Veterinary
Clinics of North America: Small Animal Practice - Special Issue:
Pediatrics - July, 1999
Congenital
Deafness and Its Recognition
George M. Strain, PhD
Professor of Neuroscience, Veterinary Physiology,
Pharmacology and Toxicology, School of Veterinary Medicine; and
Associate Vice
Chancellor, Office of Research and Graduate Studies, Louisiana State
University, Baton Rouge, Louisiana, 70803
This work was supported by Grant No. 1R15DC01128-01
from the National Institutes of Health and by a grant from the American
Kennel Club.
Synopsis
Congenital deafness in dogs and cats is primarily of the hereditary
sensorineural form associated with white pigmentation genes, although
acquired forms of deafness are possible. Highest prevalence is seen in
white cats, especially those with blue eyes, and the Dalmatian, with
many other dog breeds affected to some extent. This deafness results
from
degeneration of the cochlear blood supply at age 3 to 4 weeks,
presumably resulting from suppression of melanocytes by the white (cat)
or merle or piebald (dog) genes. Mechanism of inheritance is not
understood for most breeds. Such animals should not be bred and may
present liabilities for their owners. Objective diagnosis of deafness,
especially when unilateral, relies on the brain stem auditory evoked
response, an electrodiagnostic test where electrical activity in
response to a click stimulus is recorded from the scalp using needle
electrodes and a special purpose computer. Client counseling guidelines
are presented.
Sensory function in neonatal dogs and cats is primarily tactile,
olfactory and gustatory. The visual and auditory senses, although
partially functional at birth, exhibit significant postnatal
development:
in the dog, the eyes do not open until a puppy is 8 to 10 days of age,
the ear canals do not open until it is 12 to 13 days of age, and mature
system function up through the cortex is not present until it is 3
months of age or older.(18,22) Similar
delays are seen in the cat. As a result, disorders of these systems
frequently escape early detection.
Deafness can be described as (1) congenital or late onset,
(2) hereditary or acquired, and (3) conductive or sensorineural.(14,15)
The most commonly occurring deafness forms in dogs and cats are
congenital hereditary sensorineural deafness, late onset acquired
sensorineural deafness, and late onset acquired conductive deafness.
Distinguishing between hereditary and acquired deafness is generally
not possible
without breeding trials, although an assumption of hereditary deafness
can be made in breeds with a high prevalence of deafness. The most
common
form of deafness in young dogs and cats is congenital hereditary
sensorineural deafness, with acquired conductive and acquired
sensorineural appearing
on rare occasions.
PATHOPHYSIOLOGY OF DEAFNESS
Perception of sound first requires transmission through the outer and
middle ears to the cochlea for transduction by neural hair cells.
Perception results from (1) transmission of transduced auditory
information from the cochlea by the eighth cranial nerve to the dorsal
and ventral cochlear nuclei, the inferior colliculus, the medial
geniculate nucleus of the thalamus, and the primary and secondary
cortical auditory areas on the temporal lobe; and (2) attention to the
arriving information. Commingling of ipsilateral and contralateral
auditory information occurs at multiple steps in the ascent up the
auditory pathway. As a result, unilateral hearing loss rarely results
from lesions or disease affecting auditory structures above the eighth
nerve. Central deafness (unilateral or bilateral) in the absence of
severe neurologic disease is clinically unknown in veterinary medicine
and is not considered further here.
Conduction Deafness
Conduction deafness results from blockage of sound transmission to
the cochlea as a consequence of occlusion of the ear canal or middle
ear cavity, or from developmental defects. Occlusion may result from
excess cerumen production, from otitis externa or media, or from
foreign objects. Developmental defects, which are uncommon, may include
atresia of the tympanum or ossicles, fusion of the ossicles, or
collapse of the ear canal from cartilaginous weakness or incomplete
development. Conduction deafness may be partial or complete and may be
reduced by intervention in some cases. Clearance by the body of the
mucopurulent discharge and detritus from otitis media may require weeks
to months after termination of the infection; hence, recovery of
auditory function is delayed. Hereditary forms of conduction deafness
have not been identified in domestic species, but the appearance of
such a disorder from a spontaneous genetic defect is possible.
Congenital Acquired Sensorineural Deafness
Congenital acquired sensorineural deafness, which is uncommon, can
result from in utero or perinatal exposure to ototoxic compounds such
as maternal treatment with aminoglycoside antibiotics,21 in utero or
perinatal otitis or meningitis, anoxia, or even trauma. Breeders with
animals belonging to breeds with a high prevalence of hereditary
sensorineural deafness may suggest acquired causes of deafness rather
than confront the breeding and other implications of the presence of a
hereditary disorder. Sensorineural deafness, whether hereditary or
acquired,
is the consequence of cochlear hair cell loss through primary or
secondary
mechanisms (see below).
Congenital Hereditary Sensorineural Deafness
|
Figure
1. Cross-section of the cochlea. The organ of Corti rests on the
basilar membrane, with its hair cell cilia embedded in the tectorial
membrane. The stria vascularis on the outer margin of the scala media
secretes the endocochlear fluid of the scala media and maintains a high
K+ concentration essential to sound transduction by the hair cells.
Sensorineural
deafness can result from primary or secondary loss of cochlear hair
cells.
(From Bloom W, Fawcett DW: A Textbook of Histology, ed 10.
Philadelphia:
WB Saunders, 1975; with permission.)
|
Congenital hereditary sensorineural deafness is usually seen in dog and
cat breeds with white pigmentation. In the small number
of canine breeds where it is not associated with white pigmentation
(Doberman and other dog breeds not carrying piebald or merle genes),23
deafness
results from the type of hair cell loss that is a primary event with
unknown
cause. In breeds of dogs carrying the piebald or merle genes and breeds
of cats carrying the white gene, the hair cell loss is secondary to
degeneration of the cochlear blood supply. Figure 1 shows a
cross section of one turn of the cochlea, demonstrating the separation
of the cochlea into
three parallel ducts: the scala vestibuli, the scala media (or cochlear
duct), and the scala tympani which joins at the apex of the cochlea
with the scala vestibuli. The outer margin of the scala media is
covered by a vascular bed, the stria vascularis. The stria is
responsible for secretion of endocochlear fluid and maintenance of its
high K+ concentration which is essential to sound transduction by the
sensory hair cells. In pigment-associated hereditary deafness, this
vascular bed degenerates, resulting in secondary loss of hair cells and
deafness. The cause for the strial degeneration is unknown, but
histologic studies have demonstrated an absence of strial melanocytes,
whose presence or postnatal development is suppressed by the piebald
or merle genes. The function of melanocytes in the stria is unknown,
but
they appear to be critical to maintenance of elevated K+ levels in the
scala media and survival of the stria. Whether hair cell death is from
primary or secondary mechanisms, the loss is permanent, as mammals are
unable to regenerate cochlear neuronal tissue.
In the Dalmatian, postnatal auditory function development has been
shown to proceed normally up until 3 weeks of age, at which point the
strial degeneration produces rapid loss of hair cell function.6 A
similar time course is likely in other breeds of dogs and cats with
pigment-associated deafness, but it has not been studied. Likewise, the
time course of
congenital deafness in canine breeds not associated with white
pigmentation
has not been documented, but it is likely that deafness is present at
birth or shortly thereafter. As a consequence of the documented 3 to 4
weeks of age at which time deafness appears, hearing testing, as
described
below, is typically not performed until an animal reaches at least 5
weeks
of age.
Table 1. Breeds With Reported
Congenital Deafness
|
Akita
|
Doberman Pinscher
|
Papillon
|
American-Canadian Shepherd
|
Dalmatian
|
Puli
|
American Eskimo
|
Dappled Dachshund
|
Rottweiler
|
American Staffordshire Terrier
|
Dogo Argentino
|
Rhodesian Ridgeback
|
Australian Cattle Dog
|
English Bulldog
|
Saint Bernard
|
Australian Shepherd
|
English Bulldog
|
Schnauzer
|
Beagle Fox Terrier
|
English Cocker Spaniel
|
Scottish Terrier
|
Bichon Frise
|
English Setter
|
Sealyham Terrier
|
Border Collie
|
French Bulldog
|
Shetland Sheepdog
|
Borzoi
|
Foxhound
|
Shropshire Terrier
|
Boston Terrier
|
German Shepherd
|
Sussex Spaniel
|
Boxer Ibizan Hound
|
Great Dane
|
Maltese Tibetan Spaniel
|
Bulldog
|
Great Pyrenees
|
Siberian Husky
|
Bull Terrier
|
Jack Russell
|
Soft Coated Wheaten Terrier
|
Cardigan Welsh Corgi
|
Kuvasz Springer Spaniel
|
Tibetan Terrier
|
Catahoula Leopard Dog
|
Labrador Retriever
|
Toy Poodle
|
Cavalier King Charles
|
Miniature Poodle
|
Walker American Foxhound
|
Chihuahua Miniature Pinscher
|
mongrel
|
West Highland White Terrier
|
Chow Chow
|
Nova Scotia Duck Tolling Retriever
|
Whippet
|
Cocker Spaniel
|
Pit Bull Terrier
|
Old English Sheepdog
|
Collie Norwegian Dunkerhound
|
Pointer
|
Italian Greyhound
|
A wide variety of breeds of
dogs have been reported to have congenital deafness (see Table 1);
not all of these cases of deafness have been shown to result from
hereditary causes. The breeds for which the prevalence is known to
be high are highlighted in bold, although similar high rates may occur
in other breeds that do not yet routinely receive testing. Prevalence
rates
measured by the author are shown in Table 2 for the canine
breeds
most often presented for hearing testing services. The highest rates
are
seen in Dalmatians, of which 30% are deaf in one or both ears; rates in
other strongly affected breeds range from 8% to 20%. Typically, there
are two to three unilaterally deaf animals for every bilaterally deaf
animal. In breeds with white versus non-white phenotypes (Bull Terrier,
English Cocker Spaniel), there is a clear increased prevalence in the
white
phenotype. Prevalence rates for pure feline breeds have not been
measured,
but are highest for the breeds carrying the white gene (Table 3),
especially in cats with blue eyes. Deafness in 256 mixed breed white
cats
was reported as 12% unilateral and 38% bilateral, for a total of 50% of
cats being affected (reviewed in Delack3). The prevalence of deafness
increases
as the number of blue eyes increases from zero to two, but not all
blue-eyed
white cats are deaf. Deafness prevalence (unilateral and bilateral) in
mixed
breed white cats was 17%, 40%, and 85% for zero, one, or two blue eyes,
respectively.(9)
Table 2. Dog Breed-Specific
Deafness Prevalence (percent)
|
Breed
|
Dogs
|
Bilaterally Hearing
|
Unilaterally
|
Bilaterally
|
Total
|
|
Tested
|
|
Deaf
|
Deaf
|
Deaf
|
Dalmatian
|
5009
|
70.2% (3510)
|
22.0% (1100)
|
8.0% (399)
|
30.0% (1499)
|
Bull Terrier
|
573
|
89.0% (510)
|
9.9% (57)
|
1.0% (6)
|
11.0% (63)
|
white
|
299
|
80.9% (242)
|
17.1% (51)
|
2.0% (6)
|
19.1% (57)
|
colored
|
272
|
97.8% (266)
|
2.2% (6)
|
0.0% (0)
|
2.2% (6)
|
English Setter
|
530
|
85.7% (454)
|
12.1% (64)
|
2.3% (12)
|
14.3% (76)
|
English Cocker Spaniel
|
828
|
92.8% (768)
|
6.2% (51)
|
1.1% (9)
|
7.2% (60)
|
parti color
|
794
|
92.6% (735)
|
6.3% (50)
|
1.1% (9)
|
7.4% (59)
|
solid color
|
34
|
97.1% (33)
|
2.9% (1)
|
0.0% (0)
|
2.9% (1)
|
Australian Cattle Dog
|
238
|
87.4% (208)
|
10.5% (25)
|
2.1% (5)
|
12.6% (30)
|
Catahoula Leopard Dog
|
48
|
31.3% (15)
|
27.1% (13)
|
41.7% (20)
|
68.8% (33)
|
Jack Russell Terrier
|
47
|
80.9% (38)
|
8.5% (4)
|
10.6% (5)
|
19.1% (9)
|
GENETICS OF DEAFNESS
Pigment-associated deafness has been reported since the last century,(1,5,8-10,12)
but the hereditary mechanisms are not yet fully understood. The merle
gene, which is responsible for the pattern of dark and light hair in
breeds such as the Collie
and Shetland Sheepdog, is a simple autosomal dominant gene.(7)
Dogs that are homozygous for the merle gene are usually deaf and
frequently solid white, blind, and sterile. Heterozygotes have an
increasing tendency to be deaf as the percent of white in the coat
increases. Although the merle geneis a dominant gene, the deafness
associated with it is not
inherited as a simple dominant (or recessive) disorder.
The piebald and extreme piebald genes, which are responsible for white
hair in nonmerle breeds of dogs, are simple autosomal recessive genes.(7)
As a result, in breeds with major white areas on the
body, the animals are homozygous. An example is the Dalmatian, all of
which are breed are homozygous for the extreme piebald gene. The
underlying coat color of black (dominant) or liver
(recessive) is covered with white by the extreme piebald gene, and
spots
are produced through the white by the dominant ticking gene. The
lightness
or heaviness of the spotting is thus controlled by the ticking gene
and not the extreme piebald gene, and it is not a factor in the
prevalence
of deafness.(19) Based on studies of
the Dalmatian, deafness in breeds carrying the piebald genes is neither
simple recessive nor dominant. Breeding of bilaterally hearing parents
routinely produces deaf offspring; thus, the mechanism is not simple
dominant. Breeding of two bilaterally deaf parents produces both deaf
and hearing offspring; the latter would not occur if the defect were
simple recessive and both parents were homozygous. There is no evidence
for X-linked or mitochondrial hereditary mechanisms. As a consequence,
inheritance of deafness associated with the piebald genes must be
polygenic
or must involve incomplete expression or penetrance, or some
combination.
Molecular genetic studies of deafness disorders in humans and mice
suggest
that this deafness may result from a defect in a gene responsible for
regulation
of the piebald genes such as one of the homeobox class of genes.
Evidence
for this comes from further findings in Dalmatians. A patch in
Dalmatians
is a large black or liver area present at birth when the puppy is
otherwise
solid white; patches are disallowed in the Dalmatian breed standard.
The
patch appears to result from weak expression of the extreme piebald
gene,
resulting in a failure to cover the underlying coat color; patched
Dalmatians
are statistically less likely to be deaf than unpatched animals.(19)
When the extreme pieblad gene is strongly expressed, brown pigment is
suppressed in the iris, resulting in blue eyes (and frequently an
absence
of pigment in the tapetum lucidum), and melanocytes are suppressed in
the cochlear stria vascularis, resulting in deafness. Blue-eyed
Dalmatians
are statistically more likely to be deaf than brown-eyed animals.(19)
The blue eye is permitted in the breed standard in the United States
but not in Canada, Mexico, or Europe. The prevalence of deafness is
lower in Europe (combined unilateral and bilateral deafness is 21% in
the United Kingdom and 18% in Holland compared to 30% in the United
States), and
breeding away from blue eyes was shown to reduce deafness in Norway.(4)
It is not known if differences exist for deafness associated with the
two different piebald genes.
Table 3. Cat Breeds Carrying the
White (W) Coat Pigment Gene
|
White
|
White Scottish Fold
|
European White
|
White Turkish Angora
|
Foreign White
|
White American Wirehair
|
White Cornish Rex
|
White American Shorthair
|
White Devon Rex
|
White British Shorthair
|
White Manx
|
White Exotic Shorthair
|
White Persian
|
White Oriental Shorthair
|
Deafness in the Doberman Pinscher, which is accompanied by
transient vestibular dysfunction, is transmitted by a simple recessive
mechanism.(23)
Pigment-associated congenital hereditary sensorineural deafness in the
cat is linked to the white gene, which is dominant over color and is
unrelated to albinism.(13) On occasion
these cats will have a head spot and usually have one or two blue eyes.
Although the white gene is dominant, not all carriers are deaf; thus,
deafness is not simply inherited.
BEHAVIORAL INDICATORS OF DEAFNESS
Newborn puppies and kittens with undeveloped auditory and visual
function use other sensory cues for their feeding, elimination, and
locomotion behaviors. As auditory development proceeds, they can detect
loud noises, despite the unopened ear canal. Breeders relying on this
for home testing may find themselves to have been in error at a later
date. Behavioral testing of hearing after opening of the canal relies
on detection of a response to sound stimuli in the absence of
other detectable sensory signals. These noises should be produced
outside
of the visual fields, avoiding visual cues, vibratory cues, touch, and
air movements. Behavioral testing has limited value; animal responses
rapidly
adapt even when hearing is present, stressed animals with intact
hearing
may fail to respond, and unilateral deafness cannot be detected. In
unilaterally
deaf animals, the only behavioral sign of deafness is a difficulty in
localizing the source of a sound, and many animals adapt to that also.
Behavioral
deafness detection with young animals in the home is difficult, as the
deaf young cue off the behavior of their littermates. A puppy or kitten
that does not awaken in response to a loud noise is almost certainly
bilaterally deaf, but the unilaterally deaf cannot be detected with any
reliability.
As a consequence, behavioral hearing assessment of animals in the
clinic
or home is of limited reliability, and electrodiagnostic tests are used
for objective assessment.
ELECTRODIAGNOSIS OF DEAFNESS
The most widely used electrodiagnostic test of hearing
is the brain stem auditory evoked response (BAER), also known as the
brain stem auditory evoked potential (BAEP) or the auditory brain stem
response (ABR). This test was first used in veterinary research
applications
in the 1970s, and in clinical veterinary applications in the early
1980s. The BAER detects electrical activity in the cochlea and auditory
pathways in the brain in much the same way that an electrocardiogram
detects electrical activity in the heart.(17)
The response waveform consists of a series of peaks labeled with Roman
numerals: peak I is
produced by the cochlea and auditory nerve, and later peaks are
produced within the brain. The response from an ear that is deaf is an
essentially flat line. In the sample recordings in Figure 2,
the Dalmatian puppy in tracing A could hear in the tested ear, although
the Dalmatian puppy in tracing B was deaf in the tested ear, with an
essentially flat response. Because the response amplitude is quite
small, it is necessary to average the responses to multiple stimuli
(clicks) to unmask them from the other unrelated
electrical activity that is also present on the scalp (e.g.,
electroencephalographic activity, muscle activity).
|
Figure 2. Brain stem
auditory evoked responses (BAER) recorded from puppies; cat BAER appear
similar. A. A BAER from a normal dog in response to an air-conducted
click stimulus. Peak I in the response is generated by the cochlea and
VIIIth cranial nerve, while later peaks are generated in brain stem
structures. B. A
BAER from a dea0f Dalmatian. C. A BAER from a normal dog in response to
a bone-conducted click stimulus.
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The response is collected with a special computer through small
subdermal needle electrodes: one is placed in front of each ear, one is
placed at the top of the head, and a ground electrode is placed either
between and behind the eyes or on the neck. It is rare for a dog to
show any evidence of pain from the placement of the electrodes - if
anything the dog objects to the gentle restraint and the presence of
wires hanging in front of its face. A stimulus click (air-conducted)
produced by the computer is directed into the ear with a foam insert
earphone. Each ear is tested individually, and the test usually is
complete in 10 to15 minutes. Sedation or anesthesia is unnecessary
unless the dog becomes extremely
agitated, which can usually be avoided with patient and gentle
handling.
Sedation or anesthesia does not materially affect the BAER.
The click stimulus used contains most of the audible frequencies of the
dog and cat, with the exception of the very highest perceived
frequencies. Accordingly, the BAER is a frequency nonspecific test that
is more useful for detecting the presence or total absence of auditory
function without quantifying hearing loss in decibels. Assessment of
the normalcy of a response is based on identification of the presence
of Peak I within a narrow expected time frame (which varies based on
the equipment used) and the presence of the expected pattern of peaks.
With progressive hearing loss, there is a reduction in the amplitude of
the BAER peaks and an increase in peak latencies; thus, a subjective
assessment
of partial hearing loss can be made but not quantified, and differing
degrees
of loss in different frequency ranges cannot be determined. Diagnosis
of
partial hearing loss based on the BAER is done only with great caution,
as a number of technical factors can affect peak amplitude and latency
in
subjects with normal hearing.(17)
Fortunately,
partial hearing loss is rare in puppies or kittens.
The BAER demonstrates maturational changes.(22)
Because the greater portion of the BAER originates in the brain stem,
there is less postnatal development than is seen in tests of other
sensory modalities; however, postnatal development is greater in
altricial
species like the dog and cat than in precocial species like the horse
and cow. Full maturation of the BAER occurs by 40 days in the dog and
the cat. The BAER can be recorded in response to loud stimuli prior to
the opening of the ear canal, but this is not of use as it predates the
age at which deafness is manifested.
In some circumstances, it is useful to be able to differentiate between
sensorineural and conductive deafness, as this can affect breeding
decisions and whether a young animal is placed in a show home or a pet
home. When a BAER indicates deafness in an animal in which conduction
deafness might be suspected (i.e., long-eared breed, recent ear
infection), the test is repeated with a mechanical transducer that
transmits the stimulus click as a vibration through bone rather than
through air conduction.20 Because the cochlea is imbedded in bone, the
bone-conducted BAER bypasses the outer and middle ears, the sites of
conduction blockade, and directly activates the cochlea. The response
appearance is the same as an air-conducted BAER, but the peaks occur at
a shorter latency due to the shorter path traversed by the stimulus (Figure
2).
A limited availability of BAER testing sites blocks some potential
users from access, but the number of test locations is increasing
beyond the original veterinary school sites. The equipment cost of
approximately $20,000 and an absence of formal veterinary training
programs
outside of neurology residencies have impeded ready access. A listing
of available national and international sites is maintained at the
author's Web site,(16) which is also
a resource of additional information on deafness.
CLIENT COUNSELING ISSUES
Advice to clients faced with a deaf puppy or kitten varries based on
breed, animal age, home environment, unilateral versus bilateral
deafness, and other factors. Bilaterally deaf animals present a variety
of liabilities and emotional land mines, more so for dogs than for
cats. Deaf animals are at risk of injury or death from undetected
dangers such as motor vehicles. When startled, they may reflexly bite,
which is a special
concern around infants and toddlers. Anxious or aggressive
personalities may develop in deaf dogs from constantly being subjected
to startle, and familiar family members and friends may be attacked
without warning or cause. Not all deaf dogs develop these problems, and
no data exist on prevalence
rates for such events, but there is no way to predict which animals may
or may not have these experiences. Based on inherent temperament
differences,
there may also be variation between breeds in the likelihood of such
problems. Bilaterally deaf dogs are very difficult to raise and train;
as a result, they often end up in animal control shelters. From there,
they may be reclaimed by breed rescue groups, after which the cycle may
begin again. House cats present fewer problems, but outdoor cats may
fall victim to motor vehicles. An emotional cost is invariably paid by
the owners of those animals that cannot cope or adjust to their
disability, both from the perspective of
management and that of facing the decision as to whether to euthanize
an
animal with which an emotional attachment has formed. Unilateral
deafness
does not pose such problems.
Because of the many problems associated with bilaterally deaf dogs and
the surplus of available puppies, the Dalmatian Club of America has an
official position calling for the euthanasia of deaf puppies, with the
emphasis on breeders rather than new owners. Similar sentiment is held
by the official organizations of other breeds with high deafness
prevalence rates, but these groups have not adopted such an official
policy. This position has generated considerable controversy within the
purebred dog community, the general dog-owning community, the
veterinary
community, and the human deaf community, but it is probably appropriate
when divorced from emotional considerations.
Resources exist for those owners opting to keep a deaf dog. Books have
been written on living with a deaf dog,(2)
including directions for training deaf dogs to respond to American
Sign Language signs, and web pages have been posted with information
and support content. Deaf dogs and cats learn to respond to flashing
porch lights and vibrating collars,(16)
and can cue off the behavior of other animals in the household. In such
circumstances, the owner should be instructed in protecting the animal
from the inherent dangers associated with deafness: both dangers to the
deaf animal and dangers to people around the deaf animal.
Genetic counseling for owners of deaf dogs and cats cannot
be presented with total assurance because of the incomplete knowledge
of mechanisms of deafness inheritance. It can be stated that deaf
animals in breeds with a high known prevalence of either unilateral or
bilateral deafness should not be bred; unilaterally deaf animals have
the genetic defect but have one ear spared. Over the long run, such
breedings have the probability of producing more deaf animals. In
addition, it may not be advisable to breed to animals from litters
which had a high percentage of deaf animals or from lines with a
history of producing high percentages of deaf animals. The most
conservative approach avoids any possible introduction of defective
genes, but may be difficult in certain breeds. A deaf animal from one
of these breeds must be assumed to have hereditary deafness instead of
acquired deafness unless the clinical history convincingly indicates
otherwise. Because of the association between deafness and blue eyes in
the Dalmatian, it is also advisable to not breed blue-eyed dogs from
those breeds in which the blue eye is not a standard part of the breed
phenotype.
If a deaf animal is presented from a breed with no history
of notable numbers of deaf animals, the guidelines for advice are
murkier. The most conservative approach is not to breed any affected
animal, especially if the breed is one carrying piebald or merle genes,
unless the clinical history suggests a likely acquired cause such as
otitis or drug ototoxicity. Even these latter cases are not without
risk unless precedent
documentation of normal hearing exists.
In an effort to promote research to reduce deafness and provide data
for potential breeders, several national breed organizations in this
country have set up hearing registries either managed by the breed
organization (e.g., English Setter Association of America) or by a
contracted second party (e.g., Dalmatian Club of America managed by the
Institute for Genetic Disease Control in Animals, Bull Terrier Club of
America managed by the Orthopedic Foundation of America). The first
registry is closed, although the second is open and the third offers
the option of being
either closed or open to qualified members of the public. Current
canine
deafness research focuses on determining mechanisms of inheritance from
extended pedigrees and on identifying the responsible defective genes
using
molecular biological techniques.
References
1. Anderson H, Henricson B, Lundquist P-G, et al: Genetic hearing
impairment in the Dalmatian dog. Acta Oto-Laryngol Suppl 23:1, 1968
2. Becker, SC: Living With a Deaf Dog. Cincinnati, Susan Cope Becker,
1998
3. Delack JB: Hereditary deafness in the white cat. Compend Cont Ed
Pract Vet 6:609, 1984
4. Greibrokk T: Hereditary deafness in the Dalmatian: Relationship to
eye and coat color. J Amer Anim Hosp Assn 30:170, 1994
5. Hudson WR, Ruben RJ: Hereditary deafness in the Dalmatian dog. Arch
Otolaryngol 75:213, 1962
6. Johnsson LG, Hawkins JE Jr, Muraski AA, et al: Vascular
anatomy and pathology of the cochlea in Dalmatian dogs. In: de Lorenzo,
AJD (ed): Vascular Disorders and Hearing Defects. Baltimore: University
Park Press, 1973, p 249
7. Little CC: The Inheritance of Coat Color In Dogs. New York: Howell,
1957
8. Lurie MH: The membranous labyrinth in the congenitally deaf collie
and Dalmatian dog. Laryngoscope 58:279, 1948
9. Mair IWS: Hereditary deafness in the white cat. Acta Otolaryngol
Suppl 314:1, 1973
10. Mair IWS: Hereditary deafness in the Dalmatian dog. Arch
Otorhinolaryngol 212:1, 1976
11. Pujol R, Hilding D: Anatomy and physiology of the onset of auditory
function. Acta Otolaryngol 76:1, 1973
12. Rawitz B: Gehörorgan und Gehirn eines Weissen Hundes mit
blauen Augen. Morphol Arbeiten 6:545, 1896
13. Searle AG: Comparative Genetics of Coat Color in Mammals. London:
Logos Press, 1968
14. Strain GM: Congenital deafness in dogs and cats. Compend Cont Ed
Pract Vet 13:245, 1991
15. Strain GM: Aetiology, prevalence, and diagnosis of deafness in dogs
and cats. Brit Vet J 152:17, 1996
16. Strain GM: Deafness in dogs and cats. Located at:
http://www.lsu.edu/deafness/deaf.htm
17. Strain GM: Electrophysiological assessment of auditory
function. Proc. 15th ACVIM Forum 15:617.1997.
18. Strain GM, Jackson RM, Tedford BL: Postnatal development of the
visual-evoked potential in dogs. Am J Vet Res 52:231, 1991
19. Strain GM, Kearney MT, Gignac IJ, et al: Brainstem auditory evoked
potential assessment of congenital deafness in Dalmatians: associations
with phenotypic markers. J Vet Internal Med 6:175, 1992
20. Strain GM, Green KD, Twedt AC, et al: Brain stem auditory evoked
potentials from bone stimulation in dogs. Am J Vet Res 54:1817, 1993
21. Strain GM, Tedford L, Jackson RM: Postnatal development of the
brainstem auditory-evoked potential in dogs. Am J Vet Res 52:410, 1994
22. Strain GM, Merchant SR, Neer TM, et al: Ototoxicity assessment of a
gentamicin sulfate otic preparation in dogs. Am J Vet Res 56:532, 1995
23. Wilkes MK, Palmer AC: Congenital deafness and vestibular deficit in
the doberman. J Small Anim Pract 33:218, 1992
George M. Strain, PhD Comparative Biomedical Sciences
School of Veterinary
Medicine Louisiana
State University
Baton Rouge, LA
70803 (225) 578-9758
(225) 578-9895 (fax)
strain@lsu.edu
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SOME TIPS & TRICKS FROM THE EVERYDAY
PEOPLE WHO HAVE DISCOVERED THAT IT REALLY ISN’’T AS HARD AS YOU MIGHT
THINK!!
Many people
have said that deaf dogs are impossible to train, that only the best
trainers are up to the task, and that those few who do succeed are just
lucky
exceptions to the rules.
The members of DDEAF (Deaf Dog Education Action Fund), a 501(c)(3)
nonprofit organization formed to “speak on behalf of and to assist in
the betterment of life for deaf dogs everywhere,” and the thousands of
people who have taken advantage of our email list would take exception
to that. We are, for the most part, just regular people with regular
dogs that really don’t listen to us.
Getting started…
First of all, let’s talk about the things that you don’t need when you
start training a deaf dog. You don’t need a vibrating collar or any
other special tools. You don’t need to go looking for a special
trainer. You don’t need a lot of extra time or patience and you don’t
even need to worry about learning a new language. We use hand signs,
facial expressions and other body cues to communicate with each other
without ever thinking about it.
Unless your dog has recently and suddenly lost its hearing, or if it is
a new rescue that has just found its way into your life, you should not
have to worry about surprising or startling it. A healthy,
well-loved, confident dog generally does not have any adverse reaction
to life’s little unknowns. If startling is a concern for you, do it
often
and make it fun to be surprised!
From Susan Cope Becker’s “Living With A Deaf Dog”
You do need a way to get and hold your deaf dog’s attention.
Use a food treat or a favorite toy. Remember to keep your training
sessions shorter for the younger dogs. Frequency, not duration, will
be the key to your successful training times. Make sure that you and
the dog are both having a great time and you can’t go wrong.
To get your dog’s attention you might have to be a little more
creative. By stomping the floor or banging a wall to create a
vibration, or by flashing lights on and off, you can often get the
desired effect. When you’re outside, a big wave, throwing a ball or
another toy in the air or toward the dog, or walking around are all
good ways to attract attention. Movements big enough for the dog to see
will be the key.
1 There are no right signs and no wrong signs. Basic obedience
signals give you a place to start but regional sign languages allow you
to keep expanding your vocabulary.
2 Try to keep to one-handed signs so you have a free hand for the
leash or treats or anything else.
3 Make them simple motions that are easy for you to remember. You
need to be consistent if you expect the dog to be.
4 Make sure that the signs are different enough from each other to
avoid confusion. While a dog can know several different signs for a
single behavior, each sign should only get one proper response.
5 Teach a new sign slowly and exaggerate the movement until the
dog understands. Remember, too, that the greater the distance between
you and the dog, the bigger the signing motion needs to be.
And there you have it. So let’s all get out there and start
training!
The mission
of the Deaf Dog Education Action Fund is to provide education and
funding for the purpose of improving and/or saving the lives of deaf
dogs around the world.
To accomplish this, we are committed to do the following:
• To provide educational and training materials to combat the myths and
misinformation that surround deaf dogs.
• To provide a central organization where the owners and supporters of
deaf dogs can create a unified voice to increase people's understanding
about deaf dogs.
• To gather and share facts and figures about canine deafness and deaf
dog behaviors. By collecting data from those with firsthand experience,
we hope to document the realities of living with deaf dogs.
• To lobby kennel clubs and other sanctioning bodies to accept deaf
dogs into obedience, agility, and other skill competitions under the
same conditions as other competitors.
• To provide a network between those seeking to place a deaf
dog into a good home and those interested in bringing a deaf dog into
their lives.
• To establish and maintain a travel fund to assist in the
transportation of deaf dogs to their new homes and owners.
• To work toward ending the euthanization practices of the many breed
clubs and breeders who treat deafness as a death sentence for the dogs.
• To promote spaying and neutering of all pets and encourage
responsible breeding practices to reduce the pet overpopulation problem.
For More information
on Training a deaf dog
EVERY YEAR THOUSANDS OF DOGS ARE KILLED SIMPLY
BECAUSE THEY ARE DEAF!
DDEAF is working with deaf dog owners around
the world to stop this injustice.
Contact us about becoming a member or to get other information
and help save a life!
back to top
Why should deaf dogs be victimised?
Is it due to lack of
understanding on our part, or perhaps we don’t have the imagination or
patience to train them?
Hear,
Hear! - A Guide to Training the Deaf Dog
Hear Hear! goes through
training a deaf dog step-by-step. It covers basic training that most
pet dog owners require, including teaching the dog to sit, lay down,
stand, walk nicely on a lead, stay, and to come back when ‘called’. It
also covers important subjects like socialisation and suggests ways of
overcoming some of the most common unwanted behaviour, like jumping up,
barking and preventing your dog becoming destructive when left on its
own. The moral issues of finding a home
for a deaf dog are also discussed.
The book costs £7.75
including UK post and packing and is available by sending a cheque made
payable to Barry Eaton - (and please remember to include your own name
and address)
United Kingdom
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United States of America
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Other Countries
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Barry Eaton,
Pine Cottage
Station Road
Chilbolton
Hampshire
SO20 6AL
United Kingdom
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For customers
in the USA, the book can be obtained from Dogwise. Please visit their
web
site on www.dogwise.com
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Germany www.animal-learn.de
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Pet Pager
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This was designed to help pet
owners to silently call their dogs from a distance. It can be also used
to dissuade or interrupt negative behaviour. It works in the same way
as a personal pager. The pet owner sends a signal to their pet, which
activates a receiver collar that vibrates when receiving a
signal. The pager is essential for
owners of deaf or partial hearing dogs.
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Useful
Websites
