blastomycosis, and how does an animal get this disease?
is a fungal disease caused by Blastomyces dermatitidis. This
fungus most commonly infects humans and animals through the
respiratory tract. After spores are inhaled, they settle in the small
airways and begin to reproduce. The organism then spreads throughout
the body to involve many organs. Rarely, infection occurs through
contamination of an open wound.
in human medicine have been largely unsuccessful in isolating the
organism from the environment, it appears that both humans and animals
become infected from particular environmental sources, most likely the
soil. In the United States, the disease is most prevalent in the warm,
moist environment found in the Ohio and Mississippi River valleys. It
is very common in the Southeastern United States.
What can I do
to rid the environment of the fungal organism?
is nothing you can do to eliminate the fungus from the environment.
The organism is ubiquitous, meaning it lives everywhere.
What are the
signs of this disease?
The fungus seems to
target certain body systems, although it is usually spread throughout
the entire body. Fever, depression, weight loss, and loss of appetite
are common clinical signs. Draining skin lesions are seen in many
cases. Some degree of respiratory distress is present in advanced
cases. Blindness may occur suddenly because the eyes are frequently
involved. Lameness, orchitis (testicular inflammation), seizures,
coughing, enlarged lymph nodes, and a variety of other signs are
The only tests which
conclusively diagnose blastomycosis are cytology and
histopathology. Cytology, the microscopic study of cells, may be
performed in the veterinarian's office on some of the fluid draining
from an open wound or aspirated from a nodule or lymph node.
Histopathology is the study of cells and tissue architecture; a tissue
sample is sent away to a veterinary pathologist for review and
diagnosis. Because the organism is shed in large numbers in the
draining lesions, blastomycosis may be diagnosed in the office with
It is important to
note that there is a screening blood test (AGID) to determine
potential exposure. A positive result on this test does not equate
with infection; it only shows exposure to the organism. Many humans
and animals have positive screening tests, but this does not mean that
they have (or had) blastomycosis. For that reason, the results of an
AGID test must be evaluated with other clinical findings and tests
before diagnosing blastomycosis.
Can the disease
Yes, although not all
pets will survive. Fortunately, the newest anti-fungal agent being
used, itraconazole, is well tolerated by most animals and has
relatively few side effects when compared to the agents being used
several years ago. Dogs may require several months of therapy to
successfully treat this disease.
How do I know
if my animal will survive?
There is no way to
determine this before treatment is begun, although an animal in poor
condition and with advanced disease is less likely to survive. For
many, the critical period comes in the first 24-72 hours when the drug
takes effect and the fungi begin to die. The lungs harbor a large
number of organisms. A severe inflammatory response may occur as
treatment takes effect and the organisms begin to die in the lungs.
Respiratory distress may be a significant problem in the first few
days of therapy. The animal's chest will be x-rayed prior to therapy
to determine the presence and significance of a fungal pneumonia,
although the chest x-ray cannot predict the outcome of treatment.
Relapse of infection
is more common when the organism involves the nervous system, the
testicles, or the eyes. Many drugs have difficulty penetrating the
natural barriers of the nervous system, and these infections are hard
to treat. Male dogs may need to be neutered to remove this potential
source of organism. For similar reasons, one or both eyes may be
removed, especially if the pet has already been blinded by the
disease. The risk of relapse is very real with this disease, even
though treatment appears successful.
Am I at risk of
infection from my animal?
Studies on the
fungus have found that once an animal is infected, the organism enters
a different form or phase that does not appear to be infectious to
other animals or to humans. However, strict hygiene should be followed
in handling the draining lesions. The use of protective gloves and
thorough hand washing should follow contact with these animals.
The infected pet
does not need to be segregated from the owner or other household pets.
The true risk of infection to others probably comes from sharing the
same environment where infection occurred (i.e. soil, etc.). Because
the Blastomyces organism may be harbored near your home, we
would recommend that you advise your family physician of your pet's
diagnosis. Also, if anyone in your family falls into one of the
following categories, we would recommend that you consult with your
1. Infants or small
Elderly family members
Anyone with a known immunosuppressed state
This client information sheet is
based on material written by Ernest E. Ward Jr., DVM
2002 Lifelearn Inc. Used with permission under license.
June 29, 2004.