Zoonotic feline sporotrichosis: a small case cluster in Perth, Western Australia, and a review of previous feline cases from Australia

Abstract

Sporotrichosis is caused by species of the fungus Sporothrix that affect human and several animal species. The transmission of sporotrichosis is classically from an environmental source following penetrating injury. The alternative zoonotic route has gained attention due to the rapid and significant spread of cat‐transmitted sporotrichosis in South America and Malaysia, resulting in several thousand human and feline cases in recent decades, especially in Brazil. In Australia, sporotrichosis is sporadic and mainly related to environmental sources. Although feline sporotrichosis is rare in Australia, zoonotic transmission occurred in two of five reported cases, including a recent case cluster, which is reported in this article. The investigation of such cases in Australia is important, as cats not only represent a source of infection living in close proximity with humans, but also, they may represent sentinels for the environmental presence of the fungus. To encourage the investigation and reporting of new veterinary cases, we have reviewed Australian sporotrichosis cases in humans and cats and report a new case cluster of feline sporotrichosis in Perth, WA, Australia, with zoonotic transmission. The index case was a kitten who developed severe facial sporotrichosis with prominent involvement of the nasal planum. Two human cases – one suspected and one confirmed – are also described in the owner, who was a veterinary nurse, and the attending veterinarian, respectively, probably from handling the kitten while not wearing gloves. Later, another mature cat in the same household also became infected. The affected cats were successfully treated using combination of itraconazole and terbinafine. To the best of our knowledge, this is only the second case of cat‐transmitted sporotrichosis reported from Australia.

Sporotrichosis is caused by species of the thermally dimorphic fungus Sporothrix that affect human and several animal species, especially dogs and cats. The transmission of Sporothrix is classically from some environmental niche, that is, through the traumatic implantation of contaminated material through intact or damaged epidermis, ¹ , ² , ³ causing cutaneous lesions. The primary lesions often progress to lymphangitis, with ascending lesions following the lymphatics, ⁴ so‐called ‘sporotrichoid spread’.

Transmission of sporotrichosis can also be zoonotic, typically through scratches and bites of infected cats or even just direct contact with their lesions. In this context, sporotrichosis, a previously neglected fungal disease, has attracted attention over the last decades due to a significant increase in its prevalence, attributed to a cat‐transmitted epidemic in Brazil and other South American countries. ⁵ , ⁶ , ⁷

Sporothrix schenckii and S. brasiliensis are the species typically involved in zoonotic transmission, with the latter being primarily zoonotic and the most prevalent species in South America. ⁶ , ⁷ , ⁸ , ⁹ , ¹⁰ S. schenckii has been only sporadically involved in zoonotic transmission, ⁹ but the increased numbers of cases of sporotrichosis related to cat transmission in Malaysia highlights its potential for transition into a zoonotic disease entity. ¹¹ , ¹² , ¹³

The reason cats are central to the zoonotic transmission of sporotrichosis is apparently due to their unique susceptibility to Sporothrix infection. They usually develop severe disease with multiple skin lesions and sometimes also upper respiratory tract involvement, along with an extremely high fungal burden. ¹⁴ , ¹⁵ This makes them an efficient source of infection and also a potential sentinel for the presence of the pathogen in the environment. ¹⁶ Furthermore, the propensity for cats to groom their face with their forelimbs results in the claws often being coated with infectious propagules of sporotrichosis.

In Australia, cases of human sporotrichosis have been described since 1951 ¹⁷ and are usually related to environmental sources of S. schenckii. ¹⁸ , ¹⁹ , ²⁰ , ²¹ Reported cases of feline sporotrichosis are rare in Australia, ²² , ²³ , ²⁴ , ²⁵ with zoonotic transmission only described once, ²³ prior to the present report. The investigation of suspected cases in cats in Australia is important as cats not only represent a source of infection that is often in close association with humans, but also, they may reflect environmental contacts with the primary environmental niche of the fungus.

Therefore, the aim of the present work is to encourage the investigation and reporting of new veterinary cases. We document a small case cluster of feline sporotrichosis in Perth, WA, Australia, with zoonotic transmission, and review the previous Australian cases. To the best of our knowledge, this is the second case of cat‐transmitted sporotrichosis in Australia.

Case reports

Case 1

A 14‐week‐old female kitten (about 1.5 kg) was presented at the Halls Head Small Animal Clinic in Western Australia, with an expansive, irregular and ulcerated mass on the nasal bridge, causing significant facial deformity (Figure 1). Other signs included a clear ocular discharge from the left eye, multiple lumps on the tip of the right ear and oral ulceration extending through the upper labial and gingival mucosa.

Figure 1.

Appearance of the index case (kitten; case 1) at presentation for severe facial sporotrichosis. Note that the cat's holder is not wearing gloves.

A fine‐needle aspirate biopsy was performed on the nose mass and submitted for cytopathological examination. A smear made from the aspirate showed inflammatory cells, predominantly neutrophils and occasional macrophages, along with numerous oval to cigar‐shaped yeast‐like elements located both extracellularly and within macrophages and neutrophils, measuring 3–4 μm on their longest axis, consistent with Sporothrix spp. The source of infection was unknown, as she was previously a stray kitten.

Initially, the cat was prescribed compounded itraconazole (0.5 mL of a 5 mg/mL suspension; 2.5 mg orally SID for 2 weeks), which was replaced with fluconazole (1 mL of a 10 mg/mL solution; 10 mg orally BID for 4 weeks). The cat was also given amoxicillin clavulanate (15 mg/kg orally BID). There was obvious visible progression of the lesions (Figure 2) and the protocol was changed to licensed itraconazole (100 mg capsules Sporanox; Jansen Cilag; 10 mg/kg BID; capsule opened and divided and the dose sprinkled on and mixed with the main meal) and terbinafine(1/8 of a 250 mg tablet; Lamisil; 20 mg/kg BID), with eventual complete healing of lesions (Figure 3) and remission of clinical signs, with minimal residual scarring.

Figure 2.

Appearance of severe deforming nasal planum lesion during combination therapy with itraconazole and terbinafine. Still no gloves!

Figure 3.

The facial lesion had largely healed with some residual cicatrix formation, but an excellent cosmetic result.

Case 2

A 3‐year‐old male desexed domestic medium hair cat living in the same household also developed multiple skin lesions in the chin and the digit (Figure 4). Histopathology from a lesion in the chin showed yeast‐like cells consistent with Sporothrix spp. He was treated with Itraconazole (50 mg SID for 4 weeks) with complete resolution of the lesions.

Figure 4.

Multifocal ulcerated skin lesions in the mandibular region (A) and digit (B) of case 2.

Case 3

The veterinarian attending the cat was scratched on the finger and developed a focal lesion with lymphangitis(Figure 5A). A skin swab from the lesion was performed and submitted for fungal culture, resulting in isolation of Sporothrix sp. Matrix‐Assisted Laser Desorption Ionization – Time of Flight (MALDI‐TOF) identified the isolate as S. schenckii. The human patient was treated with itraconazole BID for 6 months, with eventual complete resolution of the lesions (Figure 5B).

Figure 5.

Focal sporotrichosis on the ring finger of a veterinarian which developed after a scratch from the infected kitten (case 1). (A) Before therapy. (B) After successful therapy with itraconazole.

Case 4

The owner of the cat, who was a veterinary nurse, also developed a skin lesion on the leg that was suspected to be sporotrichosis and it regressed with the use of a simple topical antibacterial.

Animal sporotrichosis in Australia–Review of the literature

Reported cases of animal sporotrichosis in Australia, prior to the present report, were limited to four feline cases from four different states (QLD, NSW, WA, VIC). Only one of them documented a history of zoonotic transmission.

The first report ²² concerned a 2‐year‐old neutered male Siamese from Queensland. The source of infection could not be determined. Treatment was first attempted with potassium iodide (KI), followed by ketoconazole and intravenous amphotericin B. This regimen reflected drugs available for veterinarians in 1985 when the cat was treated. The lesions relapsed 4 weeks after discharge and the owners opted for euthanasia. Postmortem examination demonstrated large numbers of yeast‐like elements within the lesions.

The second case was a 3‐year‐old neutered male domestic short‐hair from Western Australia. ²³ The animal presented initially with a single cutaneous lesion that disseminated further. S. schenckii was isolated from lesion exudate and cytology showed numerous yeast‐like cells. No source of infection was apparent. The cat was treated with ketoconazole and the lesion bathed with povidone iodine, but the disease progressed after the treatment was discontinued. This case was the first associated with zoonotic transmission in Australia, affecting the attending veterinarian that was bitten while handling the cat.

The third case of feline sporotrichosis from Australia occurred in a 10‐year‐old Siamese cat from NSW. ²⁴ The cat was presented with multiple skin lesions on the dorsal surface of one pinna. Numerous yeast‐like elements were present in cytological and histological preparations. S. schenckii was isolated in culture. Surgical excision of the pinna with clear margins resulted in complete resolution of the lesions.

The most recent fourth case, prior to the cat of the present report, was a 9‐year‐old castrated domestic short‐hair cat from Melbourne that was presented with a swelling on its nose. A Sporothrix spp. grew in culture and the ITS sequencing identified the species as within the S. pallida complex. Numerous hyphae and yeast‐like structures were observed histologically. Treatment was attempted with itraconazole and posaconazole but discontinued by the owners due to adverse effects. The lesion progressed for a while and then spontaneously regressed.

No dogs or other animals, including wildlife, have been reported with sporotrichosis in Australia.

Profile of human sporotrichosis in Australia

More than 200 cases of human sporotrichosis have been reported in Australia since the first case documented in 1951. ¹⁷ Patients ages ranged from 2.5 to 84 years‐of‐age, and the disease has been acquired in almost all regions of Australia (NSW, QLD, WA, NT, and VIC) (Figure 6), with most of the cases reported across Western and Northeastern regions. ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²³ , ²⁶ , ²⁷ , ²⁸ , ²⁹ , ³⁰ , ³¹ , ³² , ³³ , ³⁴ , ³⁵ , ³⁶ , ³⁷ , ³⁸ , ³⁹ , ⁴⁰ , ⁴¹ , ⁴² , ⁴³ , ⁴⁴

Figure 6.

Distribution and frequency of human and feline cases of sporotrichosis in Australia (1951–2024).

In most cases, the disease was believed to be environmentally acquired, with some clusters related to contaminated hay. ¹⁸ , ²⁶ , ³⁰ Many patients did not recall a previous injury, but they often had history of activities linked to sporotrichosis. ¹⁸ , ²¹ , ²⁹ , ⁴² , ⁴⁴ In four cases, skin lesions arose at the site of a previous spider or other arthropod bite. ²⁰ , ²⁸ , ³⁸ , ⁴³

In two cases, including the one described herein, zoonotic transmission was involved, resulting from contact with an infected cat. ²³ Contact with domestic and farm animals prior to the development of skin lesions was reported, ²¹ , ²⁸ , ⁴¹ including episodes of scratches by a cat and a parrot. ⁴¹ In all these cases, the animals were not thought to have sporotrichosis, so the episode could have caused an injury that served as a portal of entry, rather than having introduced the actual pathogen.

The cases were confirmed by fungal culture with growth of Sporothrix spp., histopathology ²⁹ , ⁴¹ or epidemiological linkages. ³⁰ S. schenckii was the prevalent species, ⁴⁵ followed by S. globosa. In one case, the causative species was determined to be S. pallida, which is known to be less pathogenic and uncommonly associated with clinical disease. The clinical relevance of this finding is debatable as the specimen from which it was isolated was a nail, so it could reflect contamination from the environment rather than an actual agent of disease.

Discussion

The present study describes the fifth instance of feline sporotrichosis in Australia, being the second with zoonotic involvement, ²² , ²³ , ²⁴ , ²⁵ and the first cluster of sporotrichosis related to feline transmission. This reinforces cats as a source of infection and the potential for the emergence of cat‐transmitted sporotrichosis in Australia.

Despite the global incidence of sporotrichosis being currently skewed to the zoonotic route, due to the high numbers of cat‐sourced cases in Brazil, ⁴⁶ the low number of feline cases amongst the few hundred cases in humans reported since 1951, ¹⁷ together with the environmentally acquired associations for most of the human cases, reflects the fact that sporotrichosis in Australia is so far typically associated with contamination from some environmental niche. Still, given the high susceptibility of cats to this disease, cats with sporotrichosis should be seen as potential sentinels for human exposures from the environment and documenting infected cats might therefore help prevent instances of human infection. The majority of owned cats in Australia are reported to have at least some outdoor access, ⁴⁷ which gives them the opportunity of being exposed to saprophytic pathogens, while even indoor cats are exposed to substrates such as potting mix and indoor plants.

Recording the prevalence and documenting feline cases is also important to permit early detection of outbreaks and zoonotic transmission. This is advised, as changes in the dynamics of infections have been described in both Brazil and Malaysia, ¹¹ , ¹³ , ¹⁶ , ⁴⁸ where cats became the main source of infection to other cats and to humans. Furthermore, Sporothrix brasiliensis, the causative agent driving zoonotic sporotrichosis in Brazil, ⁴⁹ has been detected in the United Kingdom in a cat brought from Brazil 3 years earlier, without history of sporotrichosis. ⁵⁰ This flags the potential for a long incubation period for the disease and reminds us that infectious agents spread more easily nowadays, even across geographical areas that do not share borders. Likewise, strains of S. schenckii implicated in cat‐transmitted sporotrichosis in Malaysia have now been described in Thailand, ⁵¹ which suggests strains from Malaysia are also succeeding in crossing transboundary barriers. Thus, the diagnosis of cases of feline sporotrichosis in Australia is important to monitor for exotic emerging strains entering the country.

Although cat‐transmitted sporotrichosis is rare in Australia, a high burden of Sporothrix organisms in cats' lesions have been reported in all Australian cases of feline sporotrichosis, ²² , ²³ , ²⁴ , ²⁵ which poses a risk of zoonotic transmission even when the causative strain is not primarily zoonotic. Even when the S. pallida complex species, a species not usually considered of clinical importance, was isolated from a cat as the causative agent of sporotrichosis, a high fungal burden was detected, including the presence of intralesional hyphae. ²⁵ This information is relevant, since little is known about the disease caused by these species, as such isolates are rare. The high fungal burden in this case suggests that cats can also be susceptible and a potential source of infection for these atypical species. The presence of hyphae is not a common finding in lesions of sporotrichosis, but it has been previously related to nasal lesions in itraconazole‐refractory cats. ¹⁴ A potential explanation for the somewhat unexpected outcome of the infection in that cat is that the causative species, although more closely related to S. chilensis, could not be determined using the currently available databases and therefore represents a new species.

Because Sporothrix burden seems high in cats with sporotrichosis independent of the causative species, we encourage feline sporotrichosis to be included in the differential diagnosis of all clinical presentations that might be consistent with the disease, allowing for specific therapeutic and public health approaches to be considered right from the start. Specifically, veterinarians, technicians, carers and anyone handling cats with such clinical signs should take appropriate precautions, as they are usually at‐risk population. ¹³ , ⁵² , ⁵³ Indeed, both cases of zoonotic transmission in Australia involved veterinarians, emphasizing this as an occupational hazard for this profession. In this cluster, a second human case resulting from zoonotic transmission from the index case was suspected, but was not confirmed definitely, as the lesion regressed before diagnostic tests could be performed. Although uncommon, spontaneous regression of skin lesions has been previously reported in human sporotrichosis. A similar cluster of feline sporotrichosis with zoonotic transmission to a veterinary technician has been recently reported in the United States, which highlights the importance for veterinarians to become informed about this disease, to take precautionary measures if necessary, therefore reducing the risk of transmission. ⁵⁴ The importance of using adequate personal protective equipment (specifically latex or nitrile gloves and long‐sleeved gowns) while handling cats that might have sporotrichosis cannot be overemphasised. Facial masks and eye shields are additionally necessary in animals with multiple cutaneous lesions and sneezing, due to the increased chance of infectious particles being propagated, for example after sneezing. ⁵²

Cats' heightened susceptibility to Sporothrix infection is poorly understood and, although host immune‐related factors are believed to play a major role, the mechanisms involved are still being explored. ¹⁵ , ⁵⁵ In regard to the present case, kittens less than 4 months do not have adaptive immunity fully developed, ⁵⁶ so that their response might not be comparable to that usually described for young adults, which comprises the age range most affected by sporotrichosis. We do not know the source of infection for the index case (kitten; Case 1) in this report as she was previously a stray cat, but it could have been potentially acquired from the mother through close contact, from another cat during fighting or playful interactions, or through contaminated environmental sources, possibly after a cat scratch injury.

Early initiation of antifungal treatment is recognised as being critical for rapidly reducing fungal burden in lesions of cats with sporotrichosis, and it is therefore recommended as a primary measure to reduce the zoonotic potential for disease spread. ⁵⁷ Although a rapid diagnosis is important to allow for the appropriate treatment, this can be challenging in regions where sporotrichosis does not occur often. In Australia, cryptococcosis is probably the main diagnosis to be differentiated from sporotrichosis in cats, as both diseases can have overlapping clinical presentations with prominent involvement of the nasal planum. ⁵² , ⁵⁸ , ⁵⁹ In addition, although yeast forms from both fungal agents are usually distinguishable, they do have some similar features ⁵² , ⁵⁸ that can be challenging to inexperienced cytologists less familiar with their morphology. ⁶⁰ The definitive diagnosis is critical as epidemiological implications of both diseases are substantially different, given the zoonotic potential of sporotrichosis, in contradistinction to cryptococcosis which is almost never zoonotic.

The present report reflects the complexity of the antifungal treatment in feline sporotrichosis, with multiple drugs and doses often attempted, and relatively long‐term courses of therapy being required. Furthermore, we could not find clinical trials or solid evidence‐based guidelines for the treatment of feline sporotrichosis that included kittens, which made the treatment more challenging in the present instance. Itraconazole monotherapy is generally considered the treatment of choice for feline sporotrichosis, but compounded formulations are strongly discouraged ⁵² because of inadequate bioavailability which makes them usually ineffective, as observed initially in the present report. The original itraconazole formulation Sporanox (capsules and liquid) is no longer available in Australia. Generic formulations such as APO‐itraconazole and Itranox remain available, but are inferior to the highly bioavailable formulation Lozanoc, which has more predictable bioavailability and requires half the dose on a milligram/kilogram basis (usually 5 mg/kg with food once a day for cats).

The first three cases of feline sporotrichosis reported in Australia were examined before the 2000s, when itraconazole had not been established as the drug of choice. Potassium iodide (KI), the first drug used in the treatment of feline sporotrichosis, re‐emerged in an oral capsules formulation as an important and cost‐effective option in Brazil, ⁶¹ typically in combination with itraconazole. Itraconazole‐KI combination therapy is highly recommended for the treatment of itraconazole‐refractory cases and cases with multiple cutaneous lesions or nasal mucosa involvement. ⁵² , ⁶¹ , ⁶² In our severely affected index case, combination therapy with itraconazole and terbinafine was eventually successful in treating the kitten with severe deforming facial sporotrichosis. This combination was effective, well tolerated and cost‐effective. Although terbinafine is one of the main options for the treatment of human sporotrichosis, ⁶³ including in combination with itraconazole, ⁶⁴ , ⁶⁵ , ⁶⁶ it has been largely unexplored in cats.

Combination therapy of itraconazole and intralesional amphotericin B has also been described as an alternative for cats with residual lesions of sporotrichosis that are refractory to itraconazole alone. This protocol seems particularly useful to treat nasal lesions, which can be challenging to achieve healing. ⁶⁷ , ⁶⁸ Posaconazole therapy was described for the treatment of the feline case due to a species related to S. pallida in Australia with good results ²⁵ and the availability of generic sustained release tablets which can be quartered has made this option much more cost‐effective than purchasing the suspension, although posaconazole does not concentrate in dermal tissues as well as the more lipid soluble itraconazole. ⁶⁹ , ⁷⁰ , ⁷¹ More studies are necessary to investigate the effectiveness of posaconazole against Sporothrix species of clinical importance. The susceptibility of Sporothrix isolates to different drugs is variable amongst different studies and geographical regions, ¹² , ⁷² , ⁷³ , ⁷⁴ , ⁷⁵ , ⁷⁶ , ⁷⁷ suggesting antifungal susceptibility tests should be pursued in clinical isolates of Sporothrix whenever this is affordable.

Conclusion

Even though feline sporotrichosis is rare in Australia, it should be included as a diagnostic possibility in cases with granulomatous to pyogranulomatous skin diseases, especially when facial involvement is pronounced. Cases with this diagnosis should be recorded in the literature. This is important for a few reasons: (1) cats may be surveying the environment, so their infection can be a sentinel for environmental niches harbouring this fungus; thereby possibly preventing human cases, as people could then be prevented for accessing at‐risk environments; (2) the detection and reporting of cases at the earliest opportunity allows for the identification of cases prior to contagion, thereby permitting appropriate actions to be taken to mitigate further spread to other cats and humans; (3) atypical cases such as the one caused by S. pallida complex species are extremely uncommon but their detection contributes to a better understanding of their epidemiology and pathogenicity of this genus. This also highlights the importance of pursuing full molecular and mass spectroscopic (MALDI‐TOF) identification of Sporothrix species, whenever possible.

Conflicts of interest and sources of funding

The authors declare no conflicts of interest or sources of funding for the work presented here.

Miranda, LHM. , Gillett, S. , Ames, Y. , Krockenberger, M. and Malik, R. , Zoonotic feline sporotrichosis: a small case cluster in Perth, Western Australia, and a review of previous feline cases from Australia. Aust Vet J. 2024;102:638–645. 10.1111/avj.13375

Data availability statement

The data that supports the findings of this study are available in the supplementary material of this article.