You may have spotted an interesting news story recently about a rare disease in cats that has been seen in the UK for the first time. Should people be worried for their cats? Should we worry about ourselves? Or has the risk been overstated? Let’s take a look today. 

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Sporothrix brasiliensis – an emerging new disease

Sporothrix brasiliensis is a fungus originating from southeast Brazil. Sporothrix species normally live in the soil at around 25°c; but certain species, including S. brasiliensis, have evolved to exist at temperatures of around 35-37°c, the body temperature of many mammals. This means that they can infect animals, frequently cats but sometimes humans, causing the disease Sporotrichosis. Infection usually occurs when an animal ingests the fungi from the environment (contaminated soil or plants for example), or the fungi contaminate a wound. However, animals (including humans) can also be infected via scratches, bites and fluids from animals carrying the fungus, again commonly cats. This makes Sporotrichosis a zoonotic disease. Sporotrichosis in humans caught from cats is called Cat Transmitted Sporotrichosis (CTS).

Sporotrichosis

Sporotrichosis is primarily a disease that causes lesions (sores, ulcers, bald patches) on the skin. In cats, infections can vary from a single self-limiting lesion to systemic disease resulting in death. Most cats have crusty, ulcerated, bleeding and pus-filled lesions. These can be found anywhere on the body but are commonly on the face. The disease can advance to infection of the nasal lining, cartilage and bone of the nose, as well as systemic infection leading to illness and death. Respiratory problems such as difficulty breathing are also seen. Disease tends to be more common in cats with suppressed immune systems as a result of other diseases. 

Human Sporotrichosis infections are similar to feline Sporotrichosis, with red rashes and ulcerations on the skin that take a number of weeks to heal. It can also progress to infections within the lungs; causing coughing, chest pain and fever symptoms; as well as infections in other parts of the body, such as the joints and central nervous system (no, it doesn’t turn you into a zombie!). S. brasiliensis tends to cause more serious disease than other Sporothrix species. As of 2020, at least one person is known to have died from S. brasiliensis infection. There are no known human-human infections. 

Increase in Infections

In recent decades, S. brasiliensis has spread beyond its original habitat to cover more of Brazil and other parts of South America. It is unknown exactly how this has occurred. But it is noted that S. brasiliensis has adaptations making it more suited to surviving inside a mammal host, and a preference for spread between animals. It has also been theorised that since rats can get Sporotrichosis; the sudden increase in cases is due to cats ingesting infected rats and becoming infected themselves. The role of climate change and a warming planet should also not be discounted in the spread of this fungus.

Due to these factors, the numbers of cases of S. brasiliensis Sporotrichosis in Brazil and other South American countries have dramatically increased. Before the 1990s, Sporotrichosis was rarely seen, and never linked to cat infections. But from ~2000 to 2017, there were over 12,000 cat-transmitted cases in Brazil’s Rio de Janeiro state alone. Some researchers theorise that dense urban environments with lots of cats (and rats?) may have increased the spread. A study of 178 patients in Rio de Janeiro found that 90% of patients with Sporotrichosis had contact with cats, and 65% had an injury from one. The previously more prevalent Sporothrix schenckii has been seen only once in humans in this area; demonstrating how much more pathogenic S. brasiliensis is. A number of dogs have also been shown to have Sporotrichosis, but there have been no infections in humans originating from dogs. 

Recent Spread

Until recently, there were no cases of S. brasiliensis outside of South America. However, infection caused by other strains of Sporothrix were seen, primarily from S. schenckii. In fact, Sporotrichosis was not seen at all in the UK until 2020, when a cat was infected with Sporothrix pallida, a similar species. Most concerning, in 2021 the first three cases of human Sporotrichosis were identified in the UK, all originating from a cat infected with S. brasiliensis. 

What’s the Story?

Let’s discuss the three British patients, as well as the relevant cat:

In 2021, a 63-year-old woman originally from southeastern Brazil (the region where S. brasiliensis originated) but living in the UK for three years with no travel back to Brazil since, visited an infectious disease clinic after a lesion on her arm had not healed in 3 weeks. The lesion originated from a cat scratch from her cat obtained while she was giving it medication. She was otherwise healthy. 

The second patient was the woman’s 30-year-old daughter 

She had also migrated from Brazil and not visited since. She also went to the clinic with an 8 week-old lesion on her finger; which was also obtained from the same cat in the same way. She was also healthy. Her son lived in the house too but was not bitten or scratched by the cat and had no disease.

The third patient was a male veterinary surgeon in his late 20s 

He had been scratched by the same cat while examining it. After 4 weeks, he developed an ulcerating lesion on his finger. Biopsies were taken that confirmed S. brasiliensis was the infectious agent. All three patients were treated with itraconazole antifungal for 6 months, and all recovered.

The cat that scratched all three humans was the likely source of the S. brasiliensis infection

He was a 9-year-old male neutered domestic long hair cat, rescued by the family while living in Brazil. He was brought over to the UK when the family emigrated and had not left since. The cat was kept indoors and was otherwise healthy until around 4 months before the human patients developed disease. The cat started developing lesions on his paws and head. The owners treated initially with antifungal medications (as they were familiar with Sporotrichosis from Brazil) and then sought veterinary care where fungal infection was confirmed. He improved on treatment, but died six months later due to unknown reasons. 

Interestingly, the family had another cat with no known symptoms (it is unknown if this cat came from Brazil) and another vet was also bitten by the first cat (who seems to have been understandably grumpy! – Ed.) but did not get infected.

Should We Be Worried?

Despite taking place a few years ago, a paper documenting the case was only released this year. The media got hold of it and naturally wrote articles. (Perhaps fuelled by the popularity of a certain fungus-based post-apocalyptic video game and TV show at the time…). Some people are therefore asking if S. brasiliensis-CTS is something we should be worried about. 

Here in the UK and in most parts of the world the risk of catching any form of Sporotrichosis is very low (readers in South America should continue to be wary around cats). Remember that in the UK we have only seen two individual cases of feline Sporotrichosis, and only three in humans, which is exceedingly rare, especially when compared to the hundreds and thousands seen in Brazil. 

Furthermore, this infection was almost certainly (though this has not been proven) picked up by the cat living as a stray in Brazil

The cat appeared to incubate the fungus for many years, as no obvious disease was noted on entry to the UK. And he only became unwell and thus presumably infectious when his immune system dropped for unknown reasons. The number of cats imported from Brazil is around 90 per year, which is a tiny proportion of all cats in the UK. A cat with no history of travel to Brazil is unlikely to become infected with S. brasiliensis. Unfortunately, there isn’t any information on whether the first cat with Sporotrichosis in the UK picked up its S. pallida infection from Brazil, elsewhere or within the UK. If it did originate from the UK, this could potentially show the risk is higher than we thought.

It is also important to emphasise that Sporotrichosis is not normally a dangerous disease in humans

This is true even for the more serious S. brasiliensis infections. Though serious complications and a single death have occurred, most cases respond well to several months of medical treatment or even resolve without treatment. Treatment in cats can be more complicated, however; with one study finding that of 266 cats treated, only 68 were cured, while 124 died. 

So, in summary, for UK-based and most readers abroad, S. brasiliensis and Sporotrichosis is not something we should be currently worrying about – exercise normal caution around all unknown cats and speak to your doctor if any cat scratch or bite does not heal. 

We Shouldn’t Be Worried… But…

Right now the risk to the UK from S. brasiliensis is exceedingly low. But this may not always remain the case for various reasons. 

Evolution

Firstly, we must consider why Sporotrichosis and CTS infections suddenly spiked in Brazil in the first place. As we discussed above, we aren’t certain, but evolution of the fungus itself seems a likely answer. Organisms evolve all the time, with S. brasiliensis clearly becoming more adept at surviving within mammals. There’s nothing to say that it will not become even more adept at this, and better able to survive and spread among mammals, or even naturally live in colder environments like the UK. We may also find it becomes more resistant to antifungals (already there are at least two different phenotypes with different susceptibilities to antifungals) thus more difficult to treat before it spreads further. 

Human Activity

The world is becoming increasingly more urban, with more and more humans living in cities. Cities are dense and mean more cats per area than in rural regions. Rats are also more common in cities, and it has been suggested that rats may lead to S. brasiliensis infections in cats too. The trend towards urbanisation isn’t likely to stop anytime soon. All of this means that as more people migrate to cities, the risk of coming into contact with an infected cat is higher. The UK is a highly urbanised country with high population density, potentially a good environment for S. brasiliensis. 

Importation

We advised that the risk from cats imported from Brazil is low, as only around 90 per year come from this region. But this may be underplaying the risk slightly. Only one cat was needed to infect three people, and it could easily have been more. We don’t know if Brazilians and their cats are going to find the UK more desirable to live in over the next few decades, but every cat brought over is a potential incubator of S. brasiliensis. 

Since the fungus appears to be able to reside in the body for a long time before a cat develops symptoms, health checks at the border may not be sufficient to stop it reaching the UK again – one research project considered whether routine ELISA blood testing for Sporothrix species was sensible for cats from at-risk regions. However, this could be complicated further due to the possibility that infected cats may travel from another second country before entering the UK (Portugal has close ties with Brazil, so native Brazilian cats migrating from Portugal and other countries may be theoretically bringing in S. brasiliensis under the radar). Certainly if the risk continues to grow, testing may be sensible.

Climate Change

Even if S. brasiliensis does not evolve to live in the chilly UK, human-driven climate change may make the UK a more suitable environment for it to live in anyway. As the world warms up, organisms of all kinds, from large birds and mammals to microscopic fungi, viruses and bacteria, are migrating further north and south. This means diseases previously considered exotic are now more common. S. brasiliensis may soon become one we should be worrying about just as much as ticks, heartworm and other previously unheard of UK diseases. 

Becoming an Epidemic or Endemic

The biggest fear from any new disease is it becoming an epidemic (a widespread outbreak) or even endemic (residing naturally in the UK environment and no longer needing to rely on the disease being transported from abroad to cause infection). Evolution would likely be the primary factor driving this, but the other factors would play a role too. The research paper on the first UK infections noted that we were lucky the cat in question was indoors-only, as should he have been allowed to go outside he may have infected other cats via bites or scratching, resulting in more infections and possibly even epidemic or endemic status (though this was unlikely). Since cat-cat transmission is common, only a few infected cats may be needed to cause this. 

In conclusion, though S. brasiliensis and Cat Transmitted Sporotrichosis probably doesn’t need to be on the average Brit’s radar yet (leave it to the mycologists and epidemiologists for now), it might be a name you see more and more over the next few decades. Time will tell whether it will truly become a problem for British cats and people. 

Too Long, Didn’t Read: Key Points

  • Sporothrix brasiliensis is a fungus originating from Brazil that can infect mammals, in particular cats
  • It causes the disease Sporotrichosis that causes skin lesions and rarely respiratory and other disease; it is often fatal in cats, but rarely in humans  
  • Most human infections result from contact with infected cats, usually in the form of a scratch or bite
  • Most infections in humans and some in cats can be treated with the antifungal itraconazole 
  • The number of cases in South America are increasing, and one cat and three human cases have recently been identified in the UK
  • The risk to the UK from S. brasiliensis is currently very low, but may increase over the next few decades 
  • The risk to people in South America remains higher, and people should follow local guidance regarding contact with cats

Sources:

Sporotrichosis

UK Infections

Infections in South America