Fungi are a large family that includes mushrooms. They live in soil and
organic material. Many types of fungi spread via airborne spores. Fungus
spores, which resist heat and can live for long periods without water, gain
entrance to the body through the respiratory tract or a break in the skin.
Fungal diseases can
be divided into two categories. There are fungi that affect only the skin or
mucous membranes, such as ringworm and thrush. In the
other category, the fungus is widespread and involves the liver, lungs, brain,
and other organs, in which case the disease is systemic.
As they age, our dogs often suffer a decline in functioning. Their memory, their ability to learn, their awareness and their senses of sight and hearing can all deteriorate. This deterioration can cause disturbances in their sleep-wake cycles, making them restless at night but sleepy during the day. It can increase their activity level (resulting, for example, in staring at objects, wandering aimlessly or vocalizing more) or decrease their activity level (leading to less self-care and poor appetite)...
Good hygiene is important when handling and caring for a dog with any fungal
infection. The risk to humans is low, but these are difficult diseases to
This disease is found in the central United States near the Great Lakes, the
Appalachian Mountains, Texas, and the valleys of the Mississippi, Ohio, and
Missouri rivers. These areas have nitrogen-rich soil that facilitates growth of
the causative fungus (Histoplasma capsulatum). Spores are found in soil
contaminated by the dung of bats, and chickens and other birds. Spores are
breathed in by dogs, people, or other animals.
In most cases, histoplasmosis is subclinical or inapparent, occasionally
producing a mild respiratory infection. There is an acute intestinal form,
however, that attacks the small bowel and colon. The principal signs are weight
loss and intractable diarrhea. A systemic form is characterized by fever,
weight loss, vomiting,
muscle wasting, coughing,
enlargement of the tonsils and other lymph nodes, as well as involvement of the
liver, spleen, bone marrow, eyes, skin, and, rarely, the brain.
The diagnosis is made by chest X-ray, blood studies, and identification of
the histoplasma organism in cytology, biopsy, or culture specimens.
Treatment: Oral anti-fungal drugs of the imidazole group, including
ketoconazole, itraconazole, and fluconazole, are particularly effective in
treating histoplasmosis that is not life-threatening. In dogs with severe
infections, amphotericin B is often combined with one of the imidazoles.
Amphotericin B is potentially damaging to the kidneys.
Coccidioidomycosis (Valley Fever)
This is the most severe and life-threatening of the systemic fungal
diseases. Coccidioidomycosis is found in dry, dusty parts of the southwestern
United States, and in California and neighboring Mexico. (Note that
coccidioidomycosis is not the same disease as coccidiosis, a disease caused by