Alternaria species infection in nine domestic cats

Abstract

A case series of nine domestic cats with culture-confirmed Alternaria species infection is presented, with conclusions drawn regarding signalment, clinical signs, treatment and outcome. Middle aged neutered males were over-represented and all presented with cutaneous lesions involving the extremities (nose, pinnae and digits). Lesions were mainly slow-growing, poorly circumscribed nodules or plaques but some also presented as non-healing wounds. A combination of surgical excision with adjunctive medical therapy appeared to be the most successful treatment option but long courses of medical therapy were generally required and recurrence was common.

Alternaria species is a ubiquitous saprophytic fungus that is widespread in the environment ¹ and can be cultured from the skin of healthy animals. ^2,3 It is an opportunistic pathogen and can cause disease in humans ⁴ and in domestic animals. ⁵ It is a phaeohyphomycosis with characteristic hyphae that display thick walls with yeast-like swellings; the hyphae contain melanin and stain positively with Masson-Fontana silver stain. Definitive diagnosis of Alternaria species-related disease requires specific fungal culture from biopsy specimens on antibiotic enhanced Sabouraud's agar or use of appropriate polymerase chain reaction (PCR) and sequence analysis using fresh or formalin-fixed paraffin embedded tissue.

Alternaria species-related disease in human patients is well characterised. Fungal spores generally gain entry to the host via pre-existing skin lesions leading to localised infection. This usually manifests as single, poorly circumscribed cutaneous nodules or plaques, which may be fistulated or ulcerated. ^6–9 Lesions are slow growing and pigmented hyphae may be apparent. Occasionally the lesions can be associated with paronychia ¹⁰ or osteomyelitis. ^11,12 Acute and subacute systemic disease has been described but is rare and mainly seen in immunosuppressed individuals. In these cases, any organ can be affected but central nervous system involvement with localised brain abscessation is most common. ^1,13 Treatment generally involves surgical excision with or without adjunctive chemotherapy in the form of flucytosine, azoles or amphotericin B. Prolonged treatment is usually required and recurrence is common but radical surgical excision can prove curative. ¹

There have been only a handful of previous case reports describing Alternaria species infection in domestic cats ^5,14–17 and thus assumptions regarding the clinical presentation and management of cats with Alternaria species has largely been extrapolated from information relating to other saprophytic mycoses and from experience with human disease. The aim of this case series was to review clinical data from cats with culture-positive Alternaria species disease in order to compare signalment, clinical signs, diagnoses, treatment modalities and outcomes.

Between 1999 and 2002 nine cases of Alternaria species infection were identified in domestic cats in the UK following positive culture of biopsy specimens by the Mycology Reference Laboratory in Bristol. Biopsy specimens were examined directly by softening small portions of tissue with KOH (20%) under a coverslip on a microscope slide for at least 20 min and then adding an optical brightener (calcofluor white, Remel, Cambridge, UK) before squashing the coverslip down to produce a thin layer of cells. This often revealed characteristic septate hyphae and other fungal structures which, when examined by light microscopy, could be seen to be dematiaceous (darkly pigmented). Cultures were prepared by cutting blocks of tissue approximately 1 mm² and placing them on the surface of Sabouraud agar plates (glucose-peptone agar) and incubating them at 30°C. After 1–2 weeks white fluffy colonies, which often develop into darker grey or green-black colonies with time, could be seen growing from the tissue. Microscopic examination of mounts from the cultures prepared in lactofuchsin revealed typical dematiaceous septate hyphae with chains of pale brown, club-shaped, holoblastic spores with both transverse and longitudinal septa and a characteristic beak. In six of the cats Alternaria alternata was identified as the infecting species based on typical morphological characteristics of the size, shape, pigmentation and septation of the spores and the shape and length of the beak. In the remaining three cats, although the isolates were identified to genus level on morphological characteristics the isolates were very poorly sporing so the precise species identification was less certain.

Six were domestic shorthair cats and three were pedigree cats (one Abyssinian and two Maine Coons). All of the cats were neutered males and the age range was from 4 to 12 years. Most of the cats had outdoor access but two were kept exclusively indoors. Five cats presented with a single nasal lesion (bridge of the nose or nasal planum) (cats 1–5) and one with a single lesion on the left pinna (cat 6). The other cats had two or more lesions. One had lesions on the nose and left pinna (cat 7), one had a lesion on the nose plus a non-healing wound on the right hind paw (cat 8), and one cat had lesions on the nose, tail, pinna and four digits with concurrent paronychia (cat 9).

The appearance of the lesions was variable but in all cases they were poorly circumscribed and slow growing. The nasal and pinna lesions were subcutaneous nodules or plaques with or without ulceration. Although primary lesions were generally non-painful, ulceration was associated with some discomfort. In one cat an extensive nasal lesion was present, resulting in severe impairment to upper respiratory tract airflow. The digital lesions presented as non-healing wounds.

The cat with a single lesion on the left pinnae (cat 6) was treated via surgical excision with no adjunctive treatment. This proved curative with a disease free interval of over 2 years at the latest follow-up. The cat with multiple lesions (cat 9) was treated with oral itraconazole. This was given for 4 months with resolution of all the lesions except a non-healing wound remaining on one digit. There was no recurrence of the other lesions 5 months after completion of therapy but the digital lesion persisted. Further diagnostic investigations to ascertain whether Alternaria species was still present at this site were not undertaken.

The remaining seven cats all received various combinations of surgical excision and medical therapy. Four of these cats underwent multiple surgical procedures, individually receiving two, three, four and five excisions. Data regarding the precise extent of surgical margins achieved was not available. Adjunctive medical therapies included itraconazole (cats 2, 3, 4 and 5), ketoconazole (cat 8), itraconazole followed by terbinafine (cat 1) and ketoconazole followed by itraconazole and liposomal amphotericin B (cat 7). In two cats receiving itraconazole, treatment was discontinued following documentation of hepatoxicity. In another cat repeat itraconazole therapy was declined following recurrence of disease because of significant hepatic enzyme elevations noted after the first course of treatment. This cat had persistent and slowly progressive disease. In 7/9 cats treatment was assumed to be curative with disease free intervals of greater than 12 months. A summary of the clinical data for each case is presented in Table 1

Table 1.

Summary of clinical data for nine cats with culture-confirmed Alternaria species-related disease

Cat identity	Signalment	Clinical signs	Initial treatment	Outcome and further treatment
Cat 1	Maine coon, 12y, MN	Single nasal lesion	Two surgical excisions+itraconazole therapy (10 mg/kg PO sid) (4 months)	Recurrence after 7 months. Itraconazole re-started (10 mg/kg PO sid) but no improvement. Radical surgical excision+5 months terbinafine (250 mg/cat PO sid) – presumed curative (DFI 5 years)
Cat 2	DSH, 7y, MN	Nasal lesion+lesion left pinna	Three surgical excisions were performed over a 5-year period with concurrent ketoconazole therapy (10 mg/kg PO bid)	Recurrence despite a further surgical excision with concurrent itraconazole therapy (10 mg/kg PO sid) (6 months). A fifth radical surgical procedure combined with high dose itraconazole (20 mg/kg sid) and liposomal amphotericin B therapy * eventually proved curative (DFI 4 years)
Cat 3	Abyssinian, 6y, MN	Single nasal lesion	Surgical excision+itraconazole (10 mg/kg PO sid) (3 months)	Presumed curative (DFI 13 months)
Cat 4	Maine coon, 8y, MN	Single nasal lesion	Surgical excision+itraconazole (10 mg/kg PO sid) (4 months)	Recurrence following discontinuation of medical therapy. Owner declined further treatment following documentation of elevated liver enzymes after the first course of treatment
Cat 5	DSH, 10y, MN	Single nasal lesion	Itraconazole (10 mg/kg PO sid) (2 months)	Lesion reduced in size but treatment discontinued following hepatotoxicity. Surgical excision then presumed curative (DFI 21 months)
Cat 6	DSH, 6y, MN	Single nasal lesion	Surgical excision+itraconazole (10 mg/kg PO eod) (1 month)	Recurrence 2 months post surgery. Itraconazole re-instigated (10 mg/kg PO sid) for 1 month but discontinued following hepatotoxicity. Radical surgical excision then presumed curative (DFI 48 months)
Cat 7	DSH, 8y, MN	Nasal mass+non-healing wound right hind paw	Two surgical excisions were performed 3 years apart with recurrence following each procedure.	A third surgery was combined with 1 month of ketoconazole (10 mg/kg PO bid) treatment but the lesions again recurred 3 months post surgery. A fourth surgery combined with 5 months of ketoconazole (10 mg/kg PO bid) was presumed curative (DFI 12 months)
Cat 8	DSH, 12y, MN	Single lesion left pinna	Surgical excision only	Presumed curative (DFI 24 months)
Cat 9	DSH, 4y, MN	Multifocal lesions (nose/tail/pinna/4 digits/paronychia)	Itraconazole only (10 mg/kg PO sid) (4 months)	Resolution of most lesions but persistence of non-healing wound on digit (stable disease 5 months later)

DSH=domestic shorthair, MN=male neutered, y=years old, DFI=disease free interval, sid=1× daily, bid=2× daily, tid=3× daily, eod=every other day, PO=per os.

^*Liposomal amphotericin B was administered twice weekly for 8 weeks. The first two doses were given at 1.5 mg/kg, the second two at 2 mg/kg and the rest at 2.5 mg/kg. The drug was reconstituted in 12 ml sterile water and then diluted in 5% dextrose saline to a concentration of 0.5 mg/ml. The total dose was given by slow intravenous infusion over 10 mins.

This is a small study with data from only nine clinical cases. However, as Alternaria species-related disease is rare in cats it is difficult to recruit patients, and to the authors knowledge this represents the largest published case series to date. The sample size was too small to provide a meaningful assessment of breed predisposition, although the inclusion of three purebred cats (including two Maine Coons) in such a small sample is interesting. All the cats were middle aged and all were neutered males suggesting a possible predisposition for this age and gender. Although most of the cats had outdoor access, two of the cats were kept exclusively indoors. As well as being a common contaminant of soil, Alternaria species is known to be prevalent indoors, particularly in moist environments such as bathrooms. ^18,19 As this is true for most environmental fungi ²⁰ a diagnosis of mycotic disease should not be discounted based on a lack of outdoor access.

As is found in human disease, Alternaria species infection in cats often appears as slow-growing, poorly circumscribed, cutaneous lesions that can be nodular or plaque like in appearance. It should also be considered as a differential diagnosis for a non-healing wound. The extremities, particularly the nose, pinnae and digits are predisposed and although the majority of lesions are focal, multifocal disease is also possible. Lesions can be locally aggressive but no systemic involvement was present in any of the cases in this series. However, cerebral involvement with other phaeohyphomycoses is reported in cats ²¹ so this possibility can not be excluded. Lesions are generally non-painful although secondary ulceration is common, resulting in discomfort.

The most common medical therapy employed for fungal diseases is the use of azoles and, as expected, these appear to be effective against Alternaria species. Their main mode of action is the inhibition of sterol synthesis via fungal cytochrome P450 but they also inhibit nucleic acid, triglyceride and fatty acid synthesis. Although fungicidal at high concentrations, these levels are rarely achieved ‘in vivo’ without unacceptable toxicity, thus they should be considered fungistatic in the majority of cases. The older imidazole drugs such as ketoconazole are generally felt to be less effective with more side effects ² and are, therefore, only advocated when costs are an issue. However, ketoconazole did appear to be effective when combined with surgery in one cat in this study (cat 7). At present the triazole drugs itraconazole and fluconazole are the most commonly used antifungal agents in veterinary medicine. As illustrated by this case series, long courses of therapy are usually required and the side-effects of azoles, particularly hepatotoxicity, can be a limiting factor. Newer second generation triazoles such as voriconazole and posaconazole have enhanced broad spectrum antifungal activity. They have not yet been used extensively in veterinary species but clinical trials suggest they may be superior for reducing fungal burdens. ^22,23 They have also proved successful against some resistant fungal infections. ²⁴

Alternatives to azole therapy include amphotericin B and terbinafine. Terbinafine is a relatively new fungicidal drug in terms of veterinary use. There has been limited experience of its use in cats but side effects are thought to be rare. It was used in combination with surgery in one cat in this study which appeared to be effective. This drug is concentrated in the skin and fat following oral dosing and has proved extremely effective for the treatment of human skin and nail infections, particularly dermatophytosis. ²⁵ Amphotericin B is a lipophilic polyene that binds to ergosterol in the fungal cell membrane inducing leakage of nutrients and electrolytes. It is generally considered to be an effective fungicidal agent. ²⁶ However, because it is poorly absorbed across the gut mucosa and skin it has traditionally been administered by intravenous injection, a route that is associated with significant nephrotoxicity. Newer protocols for this drug, including subcutaneous administration of its desoxycholate form ^26,27 and the use of more expensive liposomal intravenous formulations ^13,28 significantly reduce the risk of nephrotoxicity, now making it a more realistic option for antifungal therapy in cats. Amphotericin B was used successfully with concurrent itraconazole administration and in combination with surgery in one cat in this case series (cat 2) and the drug appeared to be well tolerated in the long term.

Surgical excision or ‘debulking’ is an important aspect of therapy and should be considered in all cases. Surgery alone can be curative if radical excision is possible. However, lesions appear to be very persistent and recurrence is common despite aggressive treatment. Therefore, a combination of surgical excision and adjunctive medical therapy should be used if surgical margins can not be guaranteed. It appears that disease may be controlled effectively using medical therapy alone but complete cure may not be achieved. Given the potential side effects of long term drug therapy this should only be advocated if the lesions are multifocal or not amenable to surgery.

In conclusion, exposure rates to Alternaria species are known to be high in the UK domestic cat population ²⁹ and cutaneous infection has now been documented in a significant number of patients. Alternaria species infection should be considered in any cat presenting with a slowly-progressive cutaneous lesion on a distal extremity that does not respond to routine antibiotic therapy. Definitive diagnosis requires culture of biopsy tissue and treatment should be aggressive. Wide surgical excision or long courses of medical therapy are indicated and combining both medical and surgical therapy may be beneficial.