The Ears And The Parasites That Can Reside
There
Carrie Padget, CVT
Vet Tech Track
2012 ISVMA Annual Conference Proceedings
Ear anatomy
The ear has 3 major parts; outer ear, middle ear, and the inner ear. The outer ear
consists of the pinna, which can be upright or floppy. The ear flap funnels sound into the
ear canal. Dogs and cats have a long narrow ear canal that makes almost a 90 degree
bend as it travels to the deeper parts of the ear. The outer ear cannel is separated from
the middle ear by the tympanic membrane, a thin membrane that is also called the
eardrum. The middle ear consists of 3 small bones, an air filled cavity called the bulla,
and a thin tube leading from the bulla to the back of the mouth. The inner ear connects
to the brain and contains nerves and centers for balance and hearing.
Otitis Externa
Dogs have many more ear problems than cats. Dogs with heavy floppy ears have the
most problems with ear infections. Some breeds have lots of hair in and around the ear
canal which causes them to develop ear infections. In addition, dogs that spend lots of
time in the water also are prone to developing ear infections.
Otitis Externa is an acute or chromic inflammation of the soft tissue of the external ear
canal. It can be either a primary or a secondary disease. The severity depends on the
interaction of predisposing, primary, and perpetuating factors. There is no sex or age
predisposition but there are factors that increase the risk of developing otitis externa.
These include: conformation-congenital stenosis (shar-pei), excessive hair (poodles);
lifestyle: grooming, swimming, excessive ear care; obstructive lesions: neoplasm,
polyps; and systemic disease: fever, immune suppression, virus.
If otitis externa is not resolved otitis media, inflammation of the middle ear, and otitis
interna, inflammation of the inner ear, may develop. Also pathologic changes
permanently alter the miroclimate within the canal, promoting colonization by
opportunistic microorganisms that may produce further inflammation. As the
inflammation progresses, dermal fibrosis followed by calcification of the auditory
cartilages and osseous metaplasia, the transformation into bony tissue, may be noted
leading to decreased flexibility, progressive stenosis, and finally obstructive ear disease.
Clinical Presentation
Clinical signs are all related to the ear and the discomfort from the otitis. The animals
commonly have head rubbing, ear scratching, or head shaking. They may also have
behavioral changes, such as aggression. The owners may report discharge and or odor
from one or both ears. A head tilt can be seen if the disease is severe or if the animal
has otitis media. The animal may have hearing deficit or auricular hematomas. Plus
there may be evidence of a generalized skin disease is possible, such as foot chewing,
face rubbing.
Physical Exam Findings
The physical exam includes a visual exam of the pinna and ear canal, as well as an
otoscopic examination. During the physical exam the following may be seen and should
noted: aural pruritus or headshaking, alopecia and excoriations on the pinna, auricular
hematomas, otic discharge, calcification / thickening of canal, inflammation, erythema,
and ulceration
During the otoscopic examination, examine the good ear first to avoid spread of infection
and to decrease resistance to examination of the possibly more painful ear. Choose an
otoscope with the appropriate sized cone for the patient. For ease of examination, the
patient should be placed on a table or large canines should be placed in a sitting
position. The head should be held in such a manner to avoid crushing the ear canal.
Hold the pinna up and out from the base of the skull to straighten the ear canal. Gently
insert the otoscope into the external ear canal and slowly advance while observing the
canal. As the cone enters the vertical canal rotate the handle of the otoscope to a
horizontal position. The tympanic membrane will then be visualized in normal ears as a
white translucent membrane.
Diagnosis
The diagnosis of otitis externa and assessment of severity should be based on a
thorough history, clinical examination finding, cytology examination, and, if indicated, the
results of bacterial culture. A radiograph of skull is only used in chronic cases to
determine patency of ear canal and rule out otitis media.
Possible reasons for certain exudate are as follows: Dark, dry, and granular typically
indicates an ear mite infection. A moist, yellow, and odiferous sample can indicate a
bacteria infection. Brown and waxy indicates a yeast infection. A microscopic
examination or culture of the sample is needed for a definitive diagnosis.
Sample Collection
Ear swab samples should always be taken before any treatments or cleaning has been
done to the ears. A sample should be collected from and differentiated between the
right and the left ear. Three samples from each ear may need to be taken. The first
sample should always be for bacteria culture, identification, and sensitivity. This is
followed by a non-sterile ear swab sample. The last swab obtained is one that has
mineral oil on the swab.
The cultures sample is obtained by placing a sterile swab (example-CopanSwab) into
ear canal and removing debris. This can be sent out to a laboratory for interpretation or
completed in-house if appropriate.
The non-sterile ear swab sample is typically used to look for bacteria and/or yeast
infection. A dry or pre-moistened with sterile water or saline swab is gently placed into
the ventral ear canal and gently rotated to obtain debris. Debris on the external portions
of the ear may also be obtained. A different swab needs to be used to obtain a sample
from the other ear. Gently roll the swab from one ear in the middle of clean slide making
two to four rows. Roll in similar fashion the swab from the other ear on a different slide.
Be sure to label which slide is from the Left and Right ear. Allow the sample to dry, than
stain with Gram stain, modified Wright’s stain (like Diff-Quick), or even New Methylene
Blue for a quick "wet prep".
Ear swab samples may contain excess amounts of cerumen, ear wax. This may
interfere with the evaluation of the sample. To minimize this effect, gentle heating of the
slide may be necessary. Passing the slide briefly through a flame or gentle heat from a
warm hair dryer may be used to dissolve the wax. Excess heat must be avoided
because it will destroy the cellular components of the sample.
The mineral oil swab is used to identify Otodectes cyanotic, ear mites. Place a drop of
oil onto two clean glass slides, one labeled for the left ear and one labeled for the right
ear. Roll a clean swab into the oil for one of the ears. Then gently place the oiled swab
into that ear ventral canal and gently rotate to obtain debris, as well as the in the external
debris. Place another drop of oil on to the microscope slide and gently roll the sample in
the oil. Complete the collection on other ear.
Microscopic Examination
Normal specimens contain squamious epithelial cells, with negligible evidence of
inflammation and few microorganisms.
Bacteria
During a bacterial otitis, a bacterial ear infection, an increase number of bacteria and/or
white blood cells will be observed in the exudate. To aid the veterinarian, the bacteria
shape, arrangement, and amount must be noted.
The stained ear swab is first scanned under 40x microscopic power. To characterize the
bacteria 100x, oil, microscopic power must be used. A slide stained with a Gram stain
will allow for shape, arrangement, and color (indicating a gram positive or gram
negative). The Diff-Quick and New Methylene Blue allow for shape and arrangement of
the bacteria to be observed.
Malassezia sp., Yeast
Yeasts of the genus Malassezia are part of the normal cutaneous in dogs. In normal
dogs with healthy skin, yeast colonizes the outer layer of the skin in very low numbers.
An infection is indicated in an ear swab smear if greater than five yeasts are seen
through out the whole slide.
The stained ear swab is first scanned under 40x microscopic power. To identify the
yeast 100x, oil, microscopic power must be used. Yeast can be observed as a cluster of
round budding cells, bowling pin shape. The bud continues to grow until it separates.
Otodectes cynotis, Ear mites
Ear mites primarily occur in the external ear canal and the infection is usually bilateral.
Ear mites may also be found on any area of the body. A common infestation site is the
tail and head region. As dogs and cats curl up to sleep, their head and ears are often in
close proximity to the base of the tail. These mites spread by direct contact and are
highly transmissible between the canine and feline species. 50% feline otitis cases are
caused by ear mites, where as only 5-10% in dogs.
The mineral oil slide with the exudate is placed under a low microscopic objective.
Otodectes eggs to adults may be seen. The eggs are large, about 200 μm in length.
The adult male has short pretarsi with wineglass-shaped growth on the distal end of
each leg. The female has growths on only the first two pairs of legs, with long hairs on
the posterior two pairs of legs. The posterior of the male has a pair of suckers used to
grasp the female during copulation.
Ear mites area fairly large and may be seen with a magnifying glass or even the unaided
eye. These mites may be identified by an otoscope, through an otoscope the mites
appear as white, motile objects.
Treatment
Treatment should be sufficiently aggressive to avoid the development of chronic
pathologic change. The primary goal is the reduction of ear canal inflammation, and to
treat all predisposing and perpetuating factors. This may include ear cleaning/flushing
and topical or oral medication.
Most tractable animals will tolerate ear cleaning and medication with minimal restraint.
Fractious animals with painful ear infections may require general anesthesia or chemical
tranquilization. The animal is held in a sitting position or sternal recumbency, using one
hand around the animal’s snout to stabilize the animal’s head.
Flushing debris from the ear canal can be of great benefit. However, flushing should
never be attempted in the face of severe inflammation, as it may lead to erosion and
ulceration of the ear canal. Before flushing, verify the patient has an intact tympanic
membrane. If the ear drum appears intact install a ceruminolytic agent or mild soapy
water to soften the ear wax using a bulb syringe or a large syringe without a needle wax
and gently massage skin over external ear canal. If tympanic membrane cannot be
seen only use sterile water or saline for flushing.
Clean and flush the ear by using either a bulb syringe or syringe without the needle with
cleaning solution like: chlorhexidine, povidone iodine, Oti-clens, Epi-otic. Be careful not
to form a seal between the instrument and the ear canal, and do not use a direct stream
on the tympanic membrane. Gently massaging the ear canal from the bottom up, this
will work the solution from the bottom of the ear canal to the opening. Use a pieces of
cotton wrapped around a finger, or a cotton ball to remove loosened debris and
discharge. Do not push cotton ball in the ear any farther than your finger will go easily.
Allow the animal to shake its head to help dislodge debris in the deeper portions of the
ear canal. Continue to flush and wipe until the ear canal and solutions on the cotton ball
comes out clean (5-10 times). The folds of skin on interior part of pinna can be cleaned
with a cotton-tipped swab.
After cleaning and flushing, rinse the ear canal with warm water or normal saline
because residual soap or other cleaning agents may be irritating and can interfere with
otic medications. To dry the ear canal use pieces of cotton and allow the animal to
shake its head. Suction via a feeding tube attached to a syringe can also be used to
remove excess liquid.
Inspect the ear canal with a clean otoscope to evaluate the thoroughness of cleaning
and to look for any lesions previously obscured by debris that now may be visible.
Finally instill prescribed medication (drops or ointment), and massage external ear canal
gently to aid in dispersal of the medication throughout the canal.
Medications
Medications prescribed will vary depending on the Veterinarian preference and the
cause of the otitis externa. For inflammation, a topical or systemic corticosteroids
treatment can be used. Topical antibiotics are used for a bacterial infections, MIC
research suggests that systemic antibiotic therapy may not be helpful and many
encourage the overgrowth of resistant strains of bacteria. Topical antifungal are typically
used during a yeast infection. Topical ivermectin, Acarexx, or milbemycin, Milbemite,
are used to treat ear mites.
Prognosis and Prevention
To prevent otitis externa, ears should be cleaned regularly. The ears must be
thoroughly dried after swimming and bathing. Clinicians should reevaluate the animal
every two weeks until the otitis externa is completely resolved. The purpose is to assess
response to therapy by noting improvement in clinical findings and performing ear
cytology examination. The prognosis of otitis externa is excellent if treated early.
Extra
Client information video on cleaning dog ears:
“How to Clean Your Dog's Ears - VetVid Episode 003”:
http://www.youtube.com/watch?v=99x64TF8ppU
Client information video on cleaning dog ears:
“How to Clean Your Dog's Ears” by the ASPCA: http://www.aspca.org/pet-care/dogcare/dog-care-ear-infections.aspx
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