Rose-thorn disease sounds like a malady of lovesick teenagers, an illness of romance reserved for budding Romeos and Juliets swooning from their first forays into passion and lovesickness, an affliction arising from the shocking stick and sting of heartbreak. The sweet name of this malady, however, in no way belies the actual crustiness of its symptoms.
Rose-thorn disease, caused by the fungal organism Sporothrix schenckii, is a classic disease of gardeners around the world. The fungus lurks in dirt, moss, and flowers, and is transmitted by a stabbing inoculation, usually on the extremities and often by the prick of a rose thorn. It most commonly arises in little old ladies tending their roses, men taming wild expanses of flora into orderly lawns and disciplined flower beds, and florists manipulating their wares. Hence: rose-thorn disease.
The infection, known as sporotrichosis, has an alarming presentation. Sores creep along the arms, tracking along the lymphatic vessels that drain your fingers and hands into the lymph nodes in your armpits. Craterous subcutaneous ulcers bloom as they crawl up the arm, with the oldest sores at the puncture site and the fresher, uglier sores further along the meandering lymphatic route. Mercifully, most infections burn out and resolve on their own in a matter of weeks to months. The disease is also rare: around 250 cases are seen annually in the United States and the incidence is believed to be higher in endemic regions throughout South America, Africa and China (1).
For for the past fifteen years, however, cases of sporotrichosis in Rio de Janeiro, Brazil, have been throwing this reliable and historical relationship between fungus and flower-lover askew. Sporotrichosis has blossomed from an uncommon fungal disease into a serious public health problem in Rio, with cases escalating beyond the sporadic few into what is now considered an unprecedented “urban endemic/epidemic phenomenon”(2). But it’s not prickly flowers or mucking about in the garden that is to blame for this fungal epidemic: it’s felines.
Today, Brazilian researchers point to a “sporotrichosis belt” in Rio de Janeiro, in which ninety percent of cases can be traced directly to cats, not gardening activities (2). This belt envelops the impoverished neighborhoods and slums on the metropolitan fringes of the city, areas of “poor sanitation, substandard housing and little or no access to health services,” factors which greatly accelerate the likelihood of severe cases of sporotrichosis (3).
This patient’s arm shows the effects of sporotrichosis, caused by the fungus Sporothrix schenckii. The first symptom is usually a small reddish painless bump. This is followed by additional bumps or nodules which open and may resemble ulcerating sores; these bumps correlate with the distribution of the lymphatics that drain the fingers and skin. Image: CDC/Dr. Lucille K. Georg.
Since 1998, cases of this once rare fungus have been steadily rising. As one infectious disease clinic in Rio de Janeiro reported, only 13 cases of sporotrichosis had been reported between 1986 and 1997 (4). But over a period of just five years, from 1998 to 2008, over 15,000 cases had been referred to the same clinic (5). Of those cases, 83 percent reported having close contact with cats while 56 percent reported suffering from scratches and bites. For those that owned these cantankerous felines, sporotrichosis infection in their pets always preceded that of its owners. As of 2010, over two thousand cases of feline-associated sporotrichosis have been treated and that number is believed to be grossly under-reported (7).
Though many animals can suffer from sporothrix infection – including, apparently, such exotic creatures as armadillos, camels, and dolphins – cats are the species most commonly afflicted (3). Their habits for lurking and keeping close contact with soil and decaying debris puts them at direct risk for infection. The fungus has been isolated from cats’ claws, their oral and nasal cavities, and from skin lesions on their furry hides.
These cats may carry an asymptomatic infection or present with ulcerating sores similar to those seen in their human counterparts. How the fungus moved beyond gardens and into the grotto isn’t clear but it’s suspected that the broad roaming movements of cats may be to blame. Male cats that have not been spayed may particularly be at risk of spreading the infection, as they more prone to engaging in fights and suffering wounds from other cats, such behaviors creating an opportunity for Sporothrix to infect and then hitchhike onwards to new locations. The fungus still relies on the same mechanism of infection in humans, a stabbing inoculation to skin - it’s just relying on a different prickly organism to do its work.
A cat with ulcerating sores caused by sporotrichosis. Image: Caroldermoid. Click for source.
Feline-transmitted sporotrichosis poses a more difficult problem for physicians treating human cases of the disease. A typical human infection with the fungus arises from transmission of the mold, those delicate filaments that spread and radiate through soil and moss. But cats spread the far more virulent form of the disease, the single-celled yeast, allowing for the spark of an infection to be take hold far more readily. In this regard, cats are, again, contributing to greater success of human infection by Sporothrix (3).
Most individuals in Rio infected with sporotrichosis suffered from other infections, including human immunodeficiency virus infection (HIV), tuberculosis, leprosy, and human T-lymphotropic virus infection (7). In these highly immunocompromised individuals, the fungus flourishes, moving beyond the lymphatics of the extremities and disseminating systemically to the lungs, bone, and brain. Some individuals who are infected may have allergic or hypersensitivity reactions to the fungi, predisposing them to hospitalization and more serious medical outcomes. A few have died from overwhelming fungal infection. Bacteria, too, can capitalize on the exposed ulcers, adding a further cause for concern and resulting in causing serious and disfiguring co-infections.
Sporotrichosis has evolved from an environmental and occupational disease to a zoonotic one, maturing beyond the flora to the fauna. Why this rose fungus has transformed into a zoonotic infection in Rio de Janeiro and reached the status of a sustained multi-decade epidemic is unknown. However, it is clearly fueled by three critical variables: the free range of both domestic and stray cats; high levels of poverty; and an overall increase in immunodeficient individuals. What is clear, though, is that this unusual fungus is no longer
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