Fungal infections are caused by a group of organisms that produce spores. They usually live on dead and decaying matter, but some live as parasites too, deriving food from their hosts. Of the innumerable species of fungi in existence, only a few are responsible for causing diseases. Soil is the major source of fungal infections. Inhalation of the fungal spores in the soil, and their entry into the body through wounds, are two ways of acquiring the infection. They can enter the body through the mouth too.
Even though fungal infections may occur in healthy dogs, those that are malnourished, severely stressed, or suffering from cancer or prolonged illnesses, seem to be especially susceptible. Dogs with lowered immunity, either because of steroid medications and immunosuppressant drugs, or due to general weakness, have higher chance of acquiring fungal infections. Long-term use of antibiotics also makes dogs prone to fungal diseases. In some cases, it may be a general infection affecting the entire body, while others may be systemic, involving only certain organs.
Aspergillosis In Dogs
It is caused by fungi belonging to the genus Aspergillus. They occur all over the world, and affect both wild and domestic animals. Starting as a respiratory disease, aspergillosis can eventually develop into a more generalized infection.
As the name indicates, it typically affects the nasal passage and the paranasal sinuses. The fungal species Aspergillus fumigates is responsible for this localized infection. Nasal aspergillosis mainly destroys certain delicate bony parts in the nose called turbinates. It is a comparatively common occurrence in canine species, and may even affect healthy dogs without any immune deficiencies. The infection rarely spreads outside the nasal passages and sinuses, but in some severe cases, it may invade the bony orbits around the eyes as well as the skull.
Certain breeds are more susceptible to nasal aspergillosis, the notable among them being Greyhounds and Collies with their long heads and narrow noses. The most obvious symptoms of this disease include a bloodstained nasal discharge accompanied by sneezing and pain. The area around the nostrils may be ulcerated, and the dog may have bleeding from the nose. Antifungal medications can cure nasal aspergillosis, but the veterinarian may need to conduct several tests to confirm the diagnosis. The drugs are administered either orally, or through a nasal infusion. Even after successful treatment of the disease, relapses may occur occasionally.
Another species called Aspergillus tereus is the main organism responsible for this generalized disease, even though a few other species also may be involved in some cases. German Shepherds are especially prone to this kind of aspergillosis. The entry of the organism into the host’s body may be through the nasal route in this infection too, but the fungus, on getting entry into the lungs, move into the blood and then spread to all other parts of the body. Apart from affecting several organs such as the kidneys and the eyes, the fungus invades the muscular and bony tissues too, including the cartilaginous discs between the vertebrae in the spine.
Though slow in progress, disseminated aspergillosis causes serious damage to the dog, increasingly incapacitating it, and even leading to complete paralysis in many cases. The initial symptoms like fever, loss of appetite, listlessness, vomiting, weight loss, swollen lymph nodes, or inflamed eyes, are not indicative of the disease. But when the dog develops back pain typical of this disease, it may lead to paralysis. Another characteristic symptom is a noticeable swelling on one leg with lameness. Outlook is rather poor in severe cases, and the dog may succumb to the disease, even though some dogs are known to have recovered with medical treatment.