Health Articles

Health Articles

Canine Blastomycosis

Recently, it has come to our attention that several cases of this fungal infection have been reported in Shar-Pei. This disease is not limited to Shar-Pei. But the loss of even one dog through the lack of knowledge and timely treatment of this disease, is one dog too many. The following articles by Drs. Vidt and Van Lienden, reprinted with the permission of ”The Barker’ magazine, identify the symptoms and treatment of this potentially fatal disease. Following are several websites, which will provide much of the technical/medical information on blastomycosis.

http://www.mc.vanderbilt.edu/peds/pidl/infect/blastomy.htm

http://www.drpetra.com/Dogs/Blastomycosis.htm

http://www.canismajor.com/dog/blstomyc.html

http://www.vetmed.wisc.edu/pbs/blasto/intro.html

http://pethealthcare.net/html/body_canine_blastomycosis.html

From Jeff Vidt, DVM, Chairman of the CSPCA Health Through Education Committee

Blastomycosis is a systemic fungal infection caused by Blastomyces dermatitides. Infection generally occurs through inhalation of the infective spores which are primarily found in the soil. The organism requires high humidity such as is found in rotting vegetation, often enriched with bird droppings and protected from direct sunlight. The disease occurs in the mid-Atlantic seaboard, north-central states and the Ohio/Mississippi/Missouri river valley regions. Once the spores reach the lungs the yeast form of the fungus develops and spreads throughout the lungs resulting in a fungal pneumonia from where it can disseminate to other tissues of the body. Besides

pneumonia, the disease can cause skin and bone lesions, disease in the eyes and central nervous system disease. Dogs appear to be highly susceptible to the disease and host factors such as immunosuppressive disease, defects in the hostès immune system or other inherited or acquired defects appear to play a role. Larger breeds and primarily the hunting breeds seem to have a higher predilection for the disease.

Clinical signs depend on the organ system affected. The respiratory from (pneumonia) is characterized by coughing, labored breathing, fever, weight loss and lymph node enlargement. Bone involvement results in lameness due to osteomyelitis. Skin lesions usually appear as abscesses or draining, ulcerated areas that exude fluid on the face, limbs, and nail beds. The most common clinical sign involving the eye is uveitis or inflammation of the eyeball itself. Signs include a ”blood shot’ eye, corneal edema, pain, and hemorrhage in the eye.

Diagnosis is based on the clinical signs, history and laboratory findings. A positive serum antibody titer provides a presumptive diagnosis but is not definitive. Chest x-rays are very helpful as area bone radiographs in cases of lameness due to bone involvement. Lymph node biopsy or fine-needle aspirates of enlarged lymph nodes may reveal the presence of the organism as can cytology of the fluid from draining skin lesions. The organism as can cytology of the fluid from draining skin lesions. The organism may be found in tracheal washes from those patients with the respiratory form of the disease.

Treatment usually involves the IV administration of amphotericin B, an antifungal drug. This drug is extremely toxic to the kidneys and is given with intravenous fluid therapy. The dose and frequency varies and depends on the protocol the veterinarian follows, the severity of the disease and the clinical condition of the dog. Other drug therapies involve the use of ketoconazole and itraconazole.

These drugs can have adverse effects on the liver. Treatment is over several months and relapses are common. In most cases, animals that are still healthy one year after completion of therapy will remain free of disease.

From Raymond Van Lienden, DVM of the Clifton Animal Clinic, Clifton, Virginia

What is blastomycosis, and how does an animal get this disease?

Blastomycosis 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. Subsequent to this, the organism spreads throughout the body to involve many organs. Infrequently, infection occurs through inoculation of an open wound.

Although researchers in human medicine have been mostly unsuccessful in reliably isolating the organism from the environment, it does appear that both humans and animals become infected from particular environmental sources, probably 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 Southeaster United States.

What can I do to rid the environment of the fungal organism?

Nothing. The organism is ubiquitous, meaning it lives everywhere.

What are the signs of this disease?

The fungus seems to have preferences for certain body systems, although it is usually disseminated (spread) throughout the entire body. Fever, depression, weight loss, and anorexia are common. Draining lesions on the skin are seen in most 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 reported.

How is blastomycosis diagnosed?

The only tests, which conclusively diagnose blastomycosis, are cytology and histopathology. Cytology, the microscopic study of cells, may be performed in the veterinarianès 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. Because the organism is shed in large numbers in the draining lesions, blastomycosis is usually diagnosed in the office with cytology.

Be aware that there is a screening blood test (AGID) to determine potential exposure. A positive result on this test does not equate to the organism. Many humans and animals have positive screening tests, but this does not mean that they have (or had) blastomycosis.

Can the disease be treated?

Yes, although not all animals will survive. Fortunately, the newest antifungal agent being used is well tolerated by most animals and has relatively few side effects when compared to the agents being used several years ago. The drug, itraconazole (Sporanox), is quite expensive. Dogs may require several months of therapy. The drug is given once daily with food.

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 infections here are hard to treat. Male dogs may need to be castrated to remove this potential source of organism. For similar reasons, one or both eyes may be removed, especially if the animal

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; this does not appear to be infectious to other animals or to humans. However, common sense would dictate that strict hygiene should be followed in handling the draining lesions. 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, which infected the pet (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 physician:

Infants or small children
Transplant patients
Chemotherapy patients
HIV/AIDS
Elderly family members
Anyone with a know immunosuppressed state.

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