Sporotrichosis, an Emerging Disease That Affects Cats, Can Be Transmitted to Humans

A study published in PLOS Pathogens describes serious, potentially fatal lesions caused by this fungal disease and highlights a rise in the number of cases (photo: Isabella Dib Gremião)

An emerging disease called sporotrichosis is spreading throughout Brazil but has not been publicized extensively except in Rio de Janeiro. Cats are the main victims of this disease, a fungal infection of the skin that causes serious damage and can be fatal if it is not treated promptly.

The disease is caused by the fungus Sporothrix sp., which lives naturally in wood, plants and soil. In Brazil, the most prevalent etiological agent is S. brasiliensis, although S. schenckii is also found to a lesser extent. Infected cats transmit the fungus by scratching and biting to other cats and dogs, as well as their owners.

Lesions in humans and dogs are not usually as severe as in cats and are rarely life threatening. Even in cats, the disease is curable, but the treatment is lengthy and expensive. Its cost is the main obstacle because the disease is most frequent among animals living in poor neighborhoods.

“Reporting of human sporotrichosis isn’t compulsory in Brazil and, as a result, we don’t know exactly how prevalent it is,” said Isabella Dib Gremião, a veterinarian at the Laboratory for Clinical Research on Domestic Animal Dermatozoonosis, part of the Oswaldo Cruz Foundation’s National Infectious Disease Medicine Institute (INI-FIOCRUZ).

“Reporting has been compulsory in Rio de Janeiro State since July 2013, owing to its hyperendemic status in the area. Over 5,000 cases in humans and 4,703 in cats were diagnosed in 2015 by INI-FIOCRUZ, the referral lab in Rio de Janeiro.”

In that year alone, there were 3,253 feline cases, according to the City of Rio de Janeiro’s health surveillance authority (Vigilância Sanitária). In 2016, the number of animals diagnosed with the disease rose 400%, to 13,536 cases, according to data covering public veterinary institutes as well as home visits and community care. The city’s health department recorded 580 cases in humans last year.

These statistics refer only to reported cases. The researchers note that underreporting must be considerable. Gremião is the first author of a paper published in the journal PLOS Pathogens on cat-to-human transmission of sporotrichosis.

Biologist Anderson Rodrigues, a professor at the Federal University of São Paulo (UNIFESP) and another author of the paper, studies the genomics of the many species of Sporothrix (there are 51, of which five are medically relevant) to compare their DNA with that of S. brasiliensis, the agent that causes the emerging disease in Brazil and by far the most virulent species.

In his postdoctoral research with a scholarship from FAPESP and a publication in 2016, Rodrigues described a new species,Sporothrix chilensis, isolated on the basis of the diagnosis of a human case in Viña del Mar, Chile.

“Our comparative analysis of the Sporothrix genomes will enable us to identify groups of genes linked specifically to virulence factors and mechanisms of survival during infection,” Rodrigues said.

“We expect our understanding of genetic diversity and physiological response in Sporothrix to increase significantly. That will be a first step toward developing better methods to control these pathogens.”

Transmission and treatment

How S. brasiliensis began infecting cats is not known. Until the number of cases increased in Rio de Janeiro, sporotrichosis was considered a very sporadic occupational disease, Rodrigues recalled.

It is often referred to as “rose gardener’s disease” since infection can result from being pricked or scratched by a contaminated rose thorn. This was what led to the first cases diagnosed in the United States in the late nineteenth century. The fungus grows naturally in soil and on the surface of plants such as rose bushes.

The first case of animal sporotrichosis in Brazil was diagnosed in 1907 in rats naturally infected in the sewers of São Paulo City. The first cases in cats occurred in the 1950s.

“For a very long time, only one or two people caught the disease each year, but in 1998, the number of cases in Rio de Janeiro began to rise,” said Professor Zoilo Pires de Camargo, head of UNIFESP’s Clinical & Molecular Mycology Laboratory and principal investigator for the Thematic Project “Molecular biology and proteomics of medically interesting fungi: Paracoccidioides brasiliensis andSporothrix schenckii”, conducted between 2010 and 2016 with support from FAPESP. Camargo supervised Rodrigues’s postdoctoral research.

The disease spread from Rio de Janeiro to other cities in the same state and from there to other states. The recent emergence of feline sporotrichosis in metropolitan São Paulo caught the attention of the researchers at UNIFESP and the Zoonosis Control Center (CCZ), where 1,093 cases have been confirmed in recent years.

There are cases of sporotrichosis throughout Southeastern and Southern Brazil. In addition, a few cases are cropping up in the Northeast as well as abroad: five cases in humans were reported in Buenos Aires in 2015.

Although other species of Sporothrix that cause this disease are found around the world, according to the researchers, the Brazilian epidemic is unique because the etiological agent attacks cats, because it became a zoonosis when infected cats began transmitting the fungus to humans, and because of the significant number of cases.

“Medical records tell us that the worst outbreak of sporotrichosis occurred in the 1940s among miners in South Africa,” Camargo said. “The origin of the infection in the 3,000-odd reported cases was the untreated wooden beams that supported the excavations and where there were colonies of Sporothrix. When they treated the timber, the epidemic ended.”

In Brazil, in addition to the lack of capacity to diagnose the disease on a large scale at the municipal, state and federal levels, strategies to combat its spread are hindered by the lack of access to suitable medication.

The reference drug is itraconazole, an expensive antifungal agent. At least four boxes per month are required for six months – two boxes to treat the animal and two for its owner, if he or she is infected. As every cat owner knows, even the most tenderly treated of these pets will scratch, especially at times of stress such as when medication has to be administered.

Infected cats continue to transmit the fungus until it is completely eliminated. The lesions usually disappear after the first or second month of treatment, but the fungus does not. “If the treatment is interrupted before six months are up, the lesions may return,” Camargo said.

The reasons for feline susceptibility to S. brasiliensis and the severity of the disease in cats are unknown. A cat with lesions will have the fungus on its paws. When it fights with another cat, or with a dog, and when it catches prey, it transmits the fungus through scratches and bites.

Brawling cats typically scratch each other’s heads, where lesions are seen most frequently, but lesions occur not only on the head. The lesions steadily destroy the victim’s epidermis, dermis, collagen, muscles and even bones. The fungus can also affect internal organs, aggravating the patient’s clinical condition.

“Pets are usually abandoned by their owners when their condition worsens to this extent,” Gremião said. “They live on the street and join the chain of transmission. If they die, they’re buried in gardens or backyards, or chucked into garbage dumps, all of which are contaminated by the fungus present in the body.”

According to Gremião, combating the outbreak of sporotrichosis requires the capacity to diagnose all cases, access to medication, and educational campaigns by the government to persuade people to care for their pets properly.