Complete hearing loss is called deafness, and it can occur in one or both ears. The deafness of both ears is called bilateral, and the one-ear is called unilateral or hemisordera. It may also happen that the dog has a higher hearing threshold compared to normal animals in one or both ears, this condition being called partial deafness (hearing loss) of one or both ears.
CAUSES OF THE DEAF
The causes of deafness in pets can be div> driving holes and sensorineural deafness. The driving deafness In dogs it is observed when there are disorders in the transmission of sound vibration to the inner ear and to the ear. Any defect or disease that affects the dog's external auditory canal, the tympanic membrane, the auditory bones and / or the middle ear can cause a deafness.
The sensorioneural deafness It occurs when there are abnormalities in the structures of the inner ear, in the cochlear nerve and / or the auditory pathway in any part of its path to the cerebral cortex. The main causes include hereditary deafness, neuronal damage from ototoxic substances (antibiotics such as gentamicin or diuretics such as furosemide) or senile deafness.
The hereditary deafness It has been reported in numerous breeds of dogs and cats. It is due to degeneration of the structures of the inner ear and spiral ganglion neurons. This process takes place during the postnatal maturation of the auditory system. The clinical signs manifest between the first weeks and the first 2 months of life. A greater predisposition to hereditary deafness has been associated in dogs with a predominantly white, blue-gray or spotted coat. The most frequently affected breeds are: Dalmatian, English Setter, Australian Sheepdog, Border Collie and Shetland Sheepdog, but it has been reported in at least 54 dog breeds, including the Argentine Bulldog, Great Dane, Boxer, Bull Terrier and Cocker Spaniel, among them.
It is assumed that hereditary deafness in dogs is predominantly of the autosomal dominant type, however, in the Bull terrier an autosomal recessive inheritance was described.
BRIEF CONCEPTS OF THE HERITAGE OF THE DEAF
The inheritance of diseases, anomalies or genetic traits is described: a) by the type of chromosome in which the abnormal gene is found (autosomal chromosome or sex chromosome), and b) in case the trait is dominant or recessive. The autosomal diseases (such as deafness) are inherited through non-sex chromosomes, and sex-linked diseases are inherited through one of the "sex chromosomes," the X chromosome (diseases are not inherited through the chromosome Y). The dominant inheritance It occurs when an abnormal gene from one of the parents is capable of causing the disease, even if the parallel gene of the other parent is normal. The abnormal gene exercises dominance over the result of the gene pair.
The recessive inheritance It occurs when both genes must be abnormal to produce the disease. If only one of the genes in the pair is abnormal, then the disease manifests slightly (animal with hemisphere or hearing loss) or does not manifest. In other words, the normal gene of the pair can replace the function of the gene, so it is said that the abnormal gene acts recessively. However, an animal with only one defective gene is called a carrier, indicating that the disorder can pass to puppies. Both parents must be carriers for the puppy to be deaf.
LIKELIHOODS OF WOUNDING THE DEAF
In the case of autosomal dominant inheritance : if one of the parents is a carrier and the other is normal, there is a 50% chance that each puppy inherits the abnormal gene and therefore the dominant trait. In other words, if we assume that in a lettuce with 4 puppies, one of the parents carries an abnormal deafness gene, the statistical expectation is: 2 normal puppies and 2 deaf puppies. This does not mean that puppies will necessarily suffer hearing loss, but it does mean that each puppy has a 50:50 chance of inheriting it. Puppies that do not inherit the abnormal gene will not develop or transmit deafness.
In the case of autosomal recessive inheritance: If both parents are carriers of an autosomal recessive trait, there is a 25% chance that a puppy will inherit the two abnormal genes and therefore manifest deafness, and a 50% chance that a puppy will inherit only one abnormal gene (thus being a carrier). In other words, assuming that in a lettuce with 4 puppies, both parents are carriers (and do not manifest hearing loss), the statistical expectation is: 1 puppy with two normal (normal) chromosomes, 2 puppies with 1 normal chromosome and another abnormal (carriers, without hearing loss), and 1 puppy with 2 abnormal chromosomes (deaf). This does not necessarily mean that this distribution will be observed, but it does mean that each of the puppies has 1 chance in 4 of inheriting the disorder and a 50:50 chance of being a carrier.
Why can a dog be deaf?
Deafness in the dog can appear as a result of three factors:
- Central: for a brain injury that reduces and cancels hearing.
- Behavioral: for an accumulation of earwax. This type of deafness is temporary: as soon as the cap is removed, you hear again without problems.
- Sensory: for an injury to the internal organs of the ear.
Breeds with a greater predisposition
Any dog of any breed can have some type of deafnessNow, there are some races that are more prone than others, the main one being the Dalmatian. Up to 8% of the copies can have it. But it is not the only one.
The Bull Terrier, the Jack Russell, the Australian Mountain Dog, the Argentine Bulldog, the English Setter and the English Cocker Spaniel also have a greater predisposition.
What types of deafness are there?
There are six types of deafness, which are:
- Acquired: the dog is born being able to hear, but at some point he becomes deaf either because he had an illness, or a wax plug, etc.
- Bilateral: Cannot hear from either ear.
- Hereditary: is deaf from birth.
- Partial: Has a limited hearing ability, but is not completely deaf.
- Total: You can't hear anything from either ear.
- Unilateral: With one ear you can hear perfectly, but with the other you hear nothing.
If your friend is deaf it is important that you continue giving him a lot of love. You need it to be happy.
Types of deafness in dogs
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The different types of deafness in dogs are:
- Bilateral deafness: The dog is deaf in both ears.
- Unilateral deafness: The dog has deafness in one of his ears and the other is fully functional.
- Partial deafness: The dog has a limited hearing ability, it is not completely deaf.
- Total deafness: the dog does not hear anything at all from both ears.
- Hereditary deafness: The lack of hearing is congenital and birth.
- Acquired deafness: the dog is born a listener, but for various reasons he is deaf at a time in his life, whether as a result of illness, a blow, etc.
As you will imagine, These types of deafness are "combinable" with each other. For example, a dog may become partially deaf in one of its ears due to an accident, or be born completely deaf to both of them and never hear anything.
Reasons that can lead to deafness in dogs
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These different types of deafness in dogs They can be a consequence of different factors:
- Behavioral: deafness is a consequence of a physical factor, a blockage in the ear canal, such as earwax or due to otitis. In this case, deafness is temporary, since when the cap is removed, the dog hears normally again.
- Sensory: deafness is due to an injury to the internal organs of the ear.
- Central: The lesion is not in the ear, but in the brain, diminishing or canceling your hearing.
MOST COMMON CAUSES IN THE DEAF IN OLD DOGS
The most common cause of deafness in dogs is the inability to drive sound into the inner part of the ear. Acute otitis with the presence of secretions, narrowing of the ear canal due to chronic otitis, presence of tumors or earwax in the ear canal, ruptured eardrum, or degeneration of the ossicles, are some of the causes. In all these cases, the dog stops responding to its name, ignores the noises that occur in its environment, does not wake up in the presence of noises, or does not respond to the stimuli of sound toys. If the problem affects only one ear, it may be more difficult to identify. Acute otitis is the cause that is usually detected more easily. The dog scratches its ears, shakes its head very often, it hurts its ears, and the presence of secretions, bad smell due to them, may become evident. It is also possible that the dog even twists the head.
However, the thickening of the walls of the auditory canal, and the consequent narrowing of the canal itself, or rupture of the eardrum, are not always evident to the naked eye. Therefore it is very important to go to the veterinarian whenever you observe any of the symptoms associated with acute otitis, or if you see that your dog stops responding to sound stimuli. The veterinarian will perform a thorough inspection of the ear, palpating and visualizing all the structures with the help of an otoscope, and it may be necessary to obtain samples, in case of observing secretions or tumors. If the duct is very inflamed, pain or the presence of a foreign object is identified, it will be necessary to sedate the dog.
Another less common cause of deafness is the involvement of the inner ear. However, as this structure is closely related to the organ of balance, it is usually accompanied by very obvious symptoms such as head tilting, vertigo, eye movements, and others. Animals exposed to loud and repetitive sounds can also suffer degeneration of the inner or middle ear. It is common in hunting dogs, as a result of the accumulation of small injuries caused by shooting.
Less frequently we find neurological and toxic causes. The neurological ones include the presence of other diseases or tumors, both in the nerves that transmit the sound information to the brain and in the brain itself. The distemper virus, or meningitis, are possible causes of deafness in dogs.
Many substances can be directly toxic to the ear. Heavy metals and water contaminants, such as mercury or arsenic, cause lesions in the inner ear. There are some antibiotics and drugs, used in chemotherapy, which can cause alterations in the dog's ear and deafness. Sometimes, deafness manifests a few weeks or months after the treatment. But there are also antiseptic products that are sometimes used to clean the ear, or some component of the drops used to treat infectious otitis, which can cause temporary or permanent deafness in especially sensitive dogs.
The diagnosis of deafness in old dogs not caused by otitis externa or media, without the presence of other signs that can guide the exact cause can be complex. The veterinarian will conduct behavioral tests (such as clapping, or blowing a whistle while out of the animal's visual field), but the evaluation of the dog's response will be subjective. Fortunately, in specialized veterinary centers, advanced neurological tests can be performed to detect if the brain identifies the sounds and responds to them or not.
Finally, mention that elderly dogs may suffer from deafness, but it is a deafness associated with age. It is what is called presbiacusia. It usually manifests during the last third of life expectancy of dogs, and develops gradually. Initially the dog loses ability to detect high frequencies, but can develop complete deafness if he lives long enough.
In any case, if your dog suffers temporary or permanent deafness that affects both ears, you should be aware of his disability and try to compensate. For example, a deaf dog will not hear the engine of a vehicle approaching on the street, which can be a danger if it is not strapped.