Sporotrichosis, Subcutaneous Mycosis
Sporotrichosis is a chronic, contagious fungal disease caused by Sporothrix schenckii, a fungus widely found in nature. The organism occurs in two forms: it grows as mold in soil and as yeast in skin. Distributed worldwide, it is particularly common in tropical areas, where high humidity and temperatures promote fungal growth. In the United States, this disease is seen most often in southern coastal regions, Missouri and Mississippi river valleys. Dogs and cats can spread the disease to humans. Infected individuals, for example, gardeners, may get infected through a cut or puncture wound. Among dogs, this disease is seen most often in hunting dogs and other dogs frequently exposed to thorns and splinters. Because cat fights and other feline behaviors have been implicated in the spread of the disease, infected animals should be isolated to prevent the organism from spreading. Keeping cats indoors during feline epidemics can reduce the risk of infection.
S. schenckii is present in soil, wood, and plants. It grows particularly well in soils rich in organic material. In warm environments with high humidity, it can also grow in plants and tree bark. Most cases of sporotrichosis are acquired from the environment, as a result of contact between broken skin and fungal spores. Penetrating wounds from dead vegetation and other items such as wood splinters, sphagnum moss, thorns, or hay are most likely to become infected. Bites, scratches, pecks, and stings from a variety of animals, birds, and insects can also transfer the organism into wounds via spores carried on the surface of the body. Rarely, inhalation can result in a pulmonary form of the disease. Sporothrix schenckii is susceptible to a variety of disinfectants including 1% sodium hypochlorite, glutaraldehyde, iodine, phenolics, and formaldehyde, but its susceptibility to 70% ethanol is questionable. The organism can be inactivated by moist heat (121°C for 15 minutes or longer).
In cats, skin lesions contain large numbers of organisms that can be transmitted through cuts and abrasions. S. schenckii from cats may also be able to enter the body through intact or minimally damaged skin. Zoonotic cases have been reported in people with no history of trauma at the inoculation site. In addition, the organisms can be found in the mouth, nasal cavity and on the nails of infected cats, facilitating transmission in bites and scratches, and in the feces. Species other than cats can spread sporotrichosis; however, the organisms on those species are very sparse and transmission is much less likely.
There are three forms of the infection: cutaneous sporotrichosis is limited to the skin and is marked by multiple nonpainful nodules, ulcers, and crusts. Cutaneous-lymphatic sporotrichosis is characterized by firm round nodules that form at the point of entry and progress to the tissues underneath the skin and lymph nodes. The cutaneous and cutaneous-lymphatic are the most common forms of the disease. In systemic sporotrichosis, bones, lungs, liver, spleen, kidneys, testes, gastrointestinal tract, and central nervous system can be affected, but this form is quite rare. Disseminated sporotrichosis is usually fatal without treatment.
Canine sporotrichosis is typically a multinodular disease. The lesions often occur on the trunk, head, and limbs. Wounds associated with fighting are most commonly found on the head, lumbar region and limbs. The disease can be diagnosed by fungal culture or direct visual observation of the organisms in lesions or discharges. Various antifungal drugs, including ketoconazole, itraconazole, and amphotericin B have been used to treat sporotrichosis in animals. Supersaturated solution of potassium iodide (SSKI) can be used in the cutaneous or lymphocutaneous forms. The solution is given orally and then continued for at least one month after the nodules completely subside. Recurrence of infection is common when treatment has not been administered for long enough period of time. Antibiotics for secondary bacterial infections are a part of treatment plan.6
- Scott, Miller, Griffin. Small Animal Dermatology
- Greene CE. Infectious Diseases of the Dog and Cat
- Rippon JW. Medical Mycology
- Scott DW. Large Animal Dermatology
- Animal Disease Information, Iowa State University
- Canine Medicine and Disease Prevention. Animal Health Publications
sporotrichosis - contagious disease in many species; may occur as skin disease as ulcerated nodules; may affect skin and lymph nodes
Sporothrix carnis - causes white mold on meat in storage
zoonosis - disease of animals transmissible to humans
pulmonary - pertaining to lungs
cutaneous - pertaining to skin
lymphocutaneous - pertaining to skin and lymph nodes