Sporotrichosis is a granulomatous disease characterized by inflamed tissue and caused by the thermal dimorphic fungus Sporothrix schenckii. Sporotrichosis affects cats and dogs, and their people, as well as a diverse array of other animals from chimpanzees, pigs, <aname="_sg_123fefa5ebfa4363b140d64517508b2c"> </aname="_sg_123fefa5ebfa4363b140d64517508b2c">and birds, to donkeys, mice, and armadillos. Like their fungi family members, the organism converts into small, budding yeastlike cells in a dog's tissues and organs — the skin, respiratory system, bones, and less-frequently, the brain.
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Although it is much rarer in dogs than cats, canine sporotrichosis can be deadly and therefore should be on any dog-owners' radar if you live in warm or sub-tropical regions of the United States. But the good news is that it's generally a benign disease in dogs, except for some rare osteoarticular and disseminated forms that can develop. Presenting in three distinct forms — cutaneous, lymphocutaneous, or disseminated — the infection is sporadic and chronic, and its animal-to-human transmission history is well-documented.
What is Sporothrix fungus and how does sporotrichosis affect a dog?
Widespread in nature throughout the world, the pathogenic fungi Sporothrix thrives in soil rich in decaying organic matter, dead vegetation, straw, hay, wood, and thorny bushes; <aname="_sg_afac775be3c642bfaf25ff6f46feda0f"> </aname="_sg_afac775be3c642bfaf25ff6f46feda0f">even rosebushes, one of the ways that people contract the infection, thus its common name, "rose gardeners disease." It is the most common subcutaneous mycotic disease in people.
Cats are the only known reservoir or vector for the infection, so roaming dogs are at significant risk if they encounter a feisty feral cat.
Also, dogs who spend a lot of time outdoors in wooded areas, such as hunting dogs like bloodhounds, Plotts, or blue tick coonhounds are undoubtedly more at risk than couch potatoes and can be infected by scratches from contaminated wood splinters or thorns as they run through the bush.
But even if your dog is a toy poodle, bulldog, or mastiff, non-sporting canines may at onetime-or-another, be in an environment that supports the fungi, or worse, find themselves in a nasty altercation with an infected cat. For example, in an ongoing sporotrichosis epidemic in Rio de Janeiro, Brazil, dogs were most often infected by sporotrichosis in fights with cats.
Infection is quick and simple, via open cuts, wounds, <aname="_sg_2750ef2b1a2a4b74942b1ea6e034c9da"> </aname="_sg_2750ef2b1a2a4b74942b1ea6e034c9da">and even minor scrapes and scratches. While the spores may enter through inhalation, this mode of infection is not as common as skin inoculation.
Sneaking into a break or tear on the surface of the skin, the fungi penetrate deeper into the dermis and subcutaneous layers of the skin tissue at the entry or inoculation site. From there, they morph into a yeastlike organism that either stays in the skin (cutaneous), spreads into the lymphatics (lymphocutaneous), or disseminates systemically throughout the body via the bloodstream (disseminated) — the worst case scenario, and potentially fatal.
Symptoms or clinical signs of sporotrichosis.
If you suspect your dog may have been infected with sporotrichosis, keep an eye out for the following symptoms which correlate to the part of the body that is affected:
- Skin nodules and ulcers: At first sign, the lesions are firm, then slowly soften, draining thick, milky liquid that is green, yellow, brown, or white.
- Bumps on the skin progress to form seeping ulcers with slightly elevated, well-defined rims.
- Respiratory difficulties such as sneezing, nasal discharge, and labored breathing or dyspnea.
- Swollen lymph nodes or lymphadenomegaly.
- Loss of weight.
Diagnosing sporotrichosis in a dog.
In addition to routine diagnostic tools such as a complete physical examination and review of medical history, diagnosis of sporotrichosis is typically confirmed by culture and microscopic examination of the fluids or exudate of biopsied tissue and the tissue itself. Also, cytology, histopathology, and immunohistochemical testing are helpful. The organism may appear in only a few or several cigar-shaped, single cells and ping-pong paddle-shaped buds may also be revealed. Here's where fluorescent antibody techniques comes in: A gold-star test is used to identify Sporothrix organisms in infected tissue. But definitive diagnosis usually requires culture which produces a true mycelium — the vegetative part of a fungus or fungus-like bacterial colony that consists of a mass of branching, thread-like hyphae — for identification of the infection.
What is the treatment for sporotrichosis?
Effective treatments for sporotrichosis are generally antifungals since antibiotics are for bacterial infections and have no effect. Steroids should never be administered to a dog with a fungal infection.
Itraconazole is considered the most effective treatment for sporotrichosis and administered up to a month beyond the point where the infection seems to have abated. Alternatively, Ketoconazole is used with good results. Terbinafine and a solution of potassium iodide have also proven to be a successful therapy. Most therapies are continued beyond the apparent clinical cure for at least 30 days.
Your dog will be monitored throughout the treatment therapy for any signs of vomiting, depression, weight loss, or more severe reactions to the medications such as iodide toxicity or cardiovascular complications.
Recovery from the fungal disease sporotrichosis and how to prevent it.
Fortunately, sporotrichosis is rare in dogs, but it's common enough to deserve attention from pet parents, particularly if your dog develops nodules or sores that refuse to heal. One way you can prevent the occurrence, or complications of an infection is to take all puncture wounds, scrapes, scratches, and cuts seriously and get prompt veterinary care.
Common sense dictates avoiding dense brush, wooded areas, and thorn-infested areas.
Living in the aftermath of a sporotrichosis infection is a simple matter of monitoring for side effects from the medications used to treat the disease. The prognosis is typically good, considering the disease is usually benign in dogs. On the other hand, if the infection disseminates or spreads systemically, the prognosis is guarded, and outcomes are often poor.
Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.