Sporotrichosis

Also known as

Rose thorn disease, rose gardener’s disease

Description

This is a disease caused by the fungus Sporothrix schenckii. The fungal infection usually affects the skin, although rare forms can affect the lungs, joints, bones, and even the brain. This fungus is often found on roses and other vegetation.

The disease in animals is rare, but most frequently seen in humans and cats, and more rarely in horses, dogs, cattle, camels, dolphins, goats, mules, birds, pigs, rats, and armadillos.

The fungus was named for Benjamin Schenck, a medical student who was the first to isolate it from a human in 1896.

This fungus is found worldwide in soil, hay, moss, and plants, so it usually affects farmers, gardeners, and agricultural workers, entering the skin through small cuts and abrasions. In rare cases of sporotrichosis that affect the lungs, the fungal spores enter through the respiratory passages.

Sporotrichosis is a sporadic, chronic, granulomatous disease (characterized by small walled-off areas of inflammation). The fungus forms branching filaments on vegetation. In the U.S. it is most commonly found in coastal regions and river valleys (wet areas). Infection usually results from direct introduction of the organism into skin wounds via contact with plants or soil or penetrating foreign bodies. Disease in the lungs, caused by inhalation of spores, is rare.

The cat may be the species with the greatest zoonotic potential (ability to spread it to humans), and transmission from cats to people has been reported without evidence of skin trauma. In contrast, transmission from other infected species appears to require contact with previously traumatized skin.

The large number of fungal spores shed from the wound and in the feces of infected cats is believed to be responsible for the increased zoonotic potential of feline sporotrichosis. Epidemics of sporotrichosis have been reported in Brazil. Data from these studies support the importance of cats in zoonotic transmission of the organism. Caretakers of infected cats were four times more likely to become infected than other people living in the same household.

Sporotrichosis may be seen in three forms: lymphocutaneous (subcutaneous nodules that progress along dermal and lymphatic vessels--also called nodular lymphangitis), cutaneous (in the skin), and disseminated. The lymphocutaneous form is the most common. Small, firm dermal to subcutaneous nodules, ¼ to 1.2 inches in diameter, develop at the site of infection. As the infection travels along the lymphatic vessels, cording and new nodules develop.

The lesions ulcerate and discharge a blood-tinged fluid. Although systemic illness is not seen initially, chronic illness may result in fever, listlessness, and depression. Respiratory signs may be seen.

The cutaneous form tends to remain localized to the site of entry, although lesions may be spread outward from that area. Disseminated sporotrichosis is rare but potentially fatal and may develop if cutaneous and lymphocutaneous forms are left untreated or if the animal is inappropriately treated with corticosteroids (which hinder immune responses and the animal’s ability to fight off the infection). Infection may spread from the initial site and travel to bones, lungs, liver, spleen, testes, GI tract, or central nervous system.

Signs

• Multiple small painless nodules on the lower legs
• Nodules develop a scab on top and may discharge a small amount of pus

Cause

Horses and cattle may contact the fungus when walking through vegetation or mud containing the fungus. Nicks and abrasions on the legs enable the fungal spores to enter the skin. The fungus can also be spread from animal to animal by direct contact with discharges from nodules on infected animals.

Successive crops of lesions/nodules may enable the disease to persist on certain animals for months.

The infection follows the lymphatic system. It goes from a person’s hand or an animal’s leg along the line of the lymphatics and may end up as a systemic infection. If you are dealing with an animal that has nodules and draining tracts, wear gloves until you know exactly what it is. If you have any little cuts or scrapes on your hands, you could get it.

This fungal infection is easily diagnosed with a biopsy or cultured.  Sporothrix is a dimorphic fungus, which means it can exist in two different forms, depending on the temperature. The form in body tissue is different from the form in the environment. This is one of the criteria used for diagnosis; in body tissue we find the yeast form.

Prevention

Isolation and treatment of any affected animals may help prevent new cases  This disease is rare in cattle, however, and unless cases have been encountered on a certain farm, people generally don’t worry about prevention—especially since the fungal spores are everywhere and it is difficult to avoid them.

Treatment

Systemic treatment with iodides (potassium iodide given orally, or sodium iodide given intravenously) will usually help clear up the infection. During IV treatment, the animal should be monitored for signs of iodide toxicity. In mild cases, local application of tincture of iodine daily to the affected areas may work.

Itraconazole is an antifungal medication that often works, when given at a dosage rate appropriate for the weight of the animal, and is often the treatment of choice for sporotrichosis. Treatment should be continued 3 to 4 weeks beyond apparent recovery. Terbinafine (another antifungal medication) has also been used successfully.