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| INDEX OF ARTICLES | WAITING ROOM | EXAM ROOM | SURGERY ROOM | X-RAY ROOM | GENERAL TOPICS | IMPORTANT TOPICS | LAB and PHARMACY | PET PHOTOS | PET SUPPLIES | PET PHARMACY |
Systemic
Fungal Diseases in Dogs...
Diseases
In Disguise
Blastomycosis,
Cryptococcosis, Coccidioidomycosis (Valley
Fever), Histoplasmosis, Lyme Disease and more...
The veterinarian looks at the
black and white patterns on the viewer in the dim light of the x-ray room.
She thinks how unusual this is
. . . a four-year old Golden Retriever in the prime of its life, stricken with
lung cancer. The radiograph doesn't lie though. The light patches
taking up space in what should be dark areas of the dog's lungs literally demand
attention, stark and unnatural, like 
potholes on a busy expressway.
How unusual, the doctor muses, to see cancer like this in such a young dog;
cancer in the lungs of any dog is almost never seen unless it has metastasized
from somewhere else in the body. And to come on so quickly!
According to the owners it was happy and energetic as it swam, played fetch and
ran with the family just two weeks ago on their vacation.
Now the dog has a fever, is losing weight and coughs frequently... the patient
is failing fast! Something just doesn't fit. The veterinarian senses
an unusual discomfort with her original diagnosis of metastatic lung cancer, a
veritable death sentence for this patient. She brings the two x-ray films
of the dog’s chest, one taken side-to-side and one front-to-back, into the
exam room where four anxious people await the doctor's diagnosis. The
depressed Golden Retriever's eyes focus upward on the doctor, ears tuned in to
the soft voice. . .
"We need to do a little more detective work. See those whitish areas
in the lungs? At first my thought was a possible cancerous condition, but
given your dog's age and the sudden onset of her sickness, I just don't believe
that's our problem. You said she was just fine on the family vacation?
Where was that?"
The astute doctor was now on the right track and refused to be led down the road
to euthanasia by a disease in disguise. Unfortunately, there are canine
patients that have not been quite so lucky as the Golden in this case; this
patient was accurately diagnosed with Blastomycosis. Vigorous and
immediate treatment was begun for this fungal disease that was acquired 350
miles from the dog's home while vacationing with its human family. It was
the first case of "Blasto" this doctor had ever seen because soil and
other conditions simply did not permit the presence of the organism in the local
environment. This case of Blastomycosis came disguised as lung cancer.
Valley Fever
This exact scenario has been played out many times - only with different actors
in different disguises. "Valley Fever" is a bad
actor and is caused by a fungal organism called Coccidioides immitis.
Unlike "Blasto", which is prevalent along river systems of
Northern Wisconsin, central Kentucky, Tennessee and Ohio, Valley Fever thrives
in arid regions of the Southwest United States. Disguised as other fungal
diseases, pneumonia, cancer, Lyme
Disease, or bacterial dermatitis, Valley Fever
can severely and permanently disable a dog if the proper detective work isn't
done to establish a diagnosis and to institute treatment.
Hiding in dusty, arid soils, the microscopically small spores of this organism are inhaled
into the lungs and
in most cases only a mild respiratory inflammation occurs as the dog’s defense
mechanisms wall off the organisms. In
more severe cases the disease can spread throughout the lungs and invade other
organs. This is called systemic
dissemination of the disease. The
lungs and long bones of the limbs are a favorite target of Coccidioides immitis.
Click on the image of Tanner on the right, a victim of Valley Fever, to see just
how troublesome this "disease in disguise" can be to properly diagnose and treat.
Fungal Diseases
We’ve all heard of ringworm. This is actually a localized surface dwelling skin fungus. This
type of fungal infection is referred to as a CUTANEOUS FUNGAL DISEASE, or a
dermatophyte. Non-invasive and rarely dangerous, it creeps along the surface of the
skin. On the other hand (no pun intended!) there are
SYSTEMIC FUNGAL DISEASES that have the propensity to invade any organ system of the body. Humans can
acquire these systemic fungal diseases from the environment, just like dogs do.
Cryptococcosis
One such disease causing organism is
Cryptococcosis. In dogs and cats the
infection is thought to gain entry into the animal via the respiratory tract.
(The specimen in the two images below are from a skin lesion on a dog.)
Cryptococcal organisms can spread to other areas of the body such as the skin,
eyes, and brain and spinal cord. This organism, as many other fungal
organisms, can infect humans.
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Microscopic views of Cryptococcosis organisms from a dog |
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A key factor in recognizing the actor behind the disguise is to garner a thorough medical history that includes noting any travel outside the dog's home territory. Every veterinarian in Northern Wisconsin is wise to the masquerading fungal disease Blastomycosis and many have treated dozens of cases. However, a veterinarian on Marco Island, Florida, might never see a case! Likewise, if a patient becomes infected with Valley Fever in Tucson, Arizona and is seen weeks later by a veterinarian in the dog’s hometown of Port Washington, N.Y. and no mention is made in the patient history of travel to an area endemic for Valley Fever, prompt diagnosis and treatment may be delayed!
BLASTOMYCOSIS, much like
Valley Fever, is a commonly misdiagnosed systemic fungal disease of dogs.
It is a great masquerader and many dogs have been euthanized or had treatment
delayed because of a diagnosis of cancer mistakenly being made. It is
acquired most often by inhalation of infective spores present in organic soils
such as are present along streams, lakes, ponds and even within the dried mud
mortar of beaver lodges. Landscaping soil and even potting soil can harbor
Blastomycosis 
organisms
and any cat or dog digging up these soils may be exposed to Blastomycosis.
Especially in dry environments where the soil may be more dusty and easily
become airborne the potential for infection with Blastomycosis is greater.
The organism is present mostly in the Mississippi, Wisconsin, and Ohio River
systems.
Blasto grows in two ways. One form, called the fungal form, occurs in the environment and the organism creates microscopic spores that, once airborne, are able to pass far into the depths of the lungs. These spores are released from the fungus when the soil is disturbed by the dog digging for gophers or simply by the dog probing the soils following the odor trails that dogs love so much. Much less common in cats than dogs, Blasto is easily inhaled into the dog's lungs.
Once there, the body's normal defense mechanisms can simply eliminate these spores and no disease results. However, if the load (numbers) of spores inhaled is very great or the dog is immune suppressed or stressed by other disease or poor diet the organisms may begin to reproduce rapidly and signs of disease occur. Once the spores have taken hold, they grow as single celled yeast forms rather than the fungal form. This is way the Blasto organism is called a biphasic organism... it can grow in the environment as a fungus and within a mammal as a yeast.
After inhalation of organisms the incubation period for Blasto can be from a few days to many weeks before any signs of disease show up. Fever, poor appetite, low grade deep cough, loss of exercise tolerance, and listlessness are cardinal signs of Blastomycosis. Similar to the other systemic fungal infections, Blastomycosis can spread throughout the body from the lungs and invade lymph nodes, joints, eye structures and skin. Often the first evidence a veterinarian has of Blastomycosis is a small draining ulcer that looks like a small abscess. Sudden blindness, lameness, and blood in the urine may be the first signs of disease... even showing up before any coughing is noticed.
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HUMAN CONTAGION: It has happened quite often that a dog will be diagnosed with Blasto and shortly thereafter the human resident of the dog's household will display malaise, fever, persistent cough and weight loss. Hopefully the physician will not be fooled by this disease in disguise and will establish a diagnosis of Blastomycosis and begin treatment. The natural question arises: Did the human get the disease from the dog? The answer 99% of the time is NO. Both human and dog generally acquire the disease from the same environmental source in the soil. Likewise the dog rarely will "get Blasto" from a human companion. The exception occurs where there is transmission of yeast organisms (remember the very small fungal spores are in the environment) directly from an open, draining lesion on the dog into an open wound or directly into the eye of a human. The transmission of infective yeast cells from dog to human or human to dog can occur and result in a localized infected lesion. Fortunately this form of contagion is very rare. |
Prevention
What is the best way to insure that a dog does not fall under the spell of
Valley Fever or another diseases in disguise?
Dr. Sheila McCullough, a veterinarian at the University of Illinois
Veterinary Teaching Hospital in Urbana, Illinois, has a suggestion based upon
her experiences with systemic fungal infections. “Providing
a thorough history is very important to obtain a full picture of what led up to
the animal becoming ill,” says Dr. McCullough. “The client should
inform the veterinarian of the patient's travel history within the past 6 months
and what the daily environment is for the pet (i.e. camping, swimming, hunting,
living near new construction or landscaping).
A thorough history is the key first step toward figuring out the puzzle.
It is just as important to keep an ongoing dialogue with your veterinarian and
to create a plan of action if the initial tests for an expected disease are
negative.”
Dr. McCullough’s point should
not be underestimated. Knowledge of
a seemingly irrelevant environmental factor can be the key information the
doctor needs to proceed toward a proper diagnosis.
Something as innocent as stating “My dog loves to dig into gopher
holes, Doctor” or “Two months ago we had soil carted in for landscaping”
can turn the doctor’s attention toward a fungal infection such as Valley
Fever.
Identification
Dr. McCullough states, “Fungal diseases often masquerade as other diseases.
The affected pets present with lethargy, lameness, poor appetite, ‘not doing
right’ and may have a fever. Treatment may also be delayed because it is
difficult to get a sample of the 
organism from a lymph node, skin cytology or
trans-tracheal wash.”
It is crucial that the organisms be identified under the microscope for establishing a positive diagnosis of a fungal disease such as Valley Fever or Blasto. Culturing infected material may take weeks and the patient simply cannot afford to wait even days for a diagnosis! Blood tests are equivocal. False positives and negatives are common.
The best and most direct method of establishing a definitive diagnosis is to gather tissue or fluid samples from infected areas such as a swollen lymph node, draining skin lesion or material coughed up by the patient. A needle biopsy of a lymph node is commonly done and can be performed without anesthesia. During the office call the veterinarian will stain the specimen cells on a microscope slide and look for the infective organisms. If organisms are seen, BINGO! Start treatment right now. If they aren’t seen, special stains at a diagnostic lab are required. The important thing to do is to BE PERSISTENT in striving to get a diagnosis for the elusive disease in disguise.
Treatment
In the past, Amphotericin B was the only known medication useful against Valley
Fever and the other systemic fungal organisms.
It had to be given intravenously and with care to keep the dose from
harming the kidneys. This medication has saved thousands of canine (and human)
lives. Recently, though,
researchers have provided us with oral medications just as effective in treating
fungal infections. The most popular
today are Itraconazole (Sporanox) and Fluconazole (Diflucan). These tablets are administered for three to six months
(sometimes even longer) and your pharmacy bill will be substantial... but your
formerly infected dog out in the yard playing fetch with the children wouldn’t
be alive without it.
Whenever your dog is sick be sure to provide your veterinarian with a detailed patient history. And you should be persistent in seeking a definitive diagnosis. Persistent detective work is your best weapon for unmasking theses diseases in disguise.
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