Zoonosis: Feline sporotrichosis

A 2-year-old, male, American shorthair cat developed progressively enlarging, draining, cavitated ulcers involving the distal portion of all extremities, the head, lateral portion of the thorax, and base of the tail (Fig 1A).

Figure 1--Lesions of sporotrichosis in a cat. The skin around the hock has a large zone of ulceration with exposure of underlying bone and ligments (A); ulcerated nodule from the lateral portion of the thorax (B); photomicrograph of an impression smear from an ulcerated nodule from a cat with sporotrichosis. Notice the numerous elongate fungal organisms within a macrophage. Wright-Giemsa stain; X 27.(a) (C); photomicrograph of a section of a dermal lesion specimen from a cat with sporotrichosis. Notice the myriads of free and extracellular organisms with dark-staining centers surrounded by a clear capsule. H&E stain; X 340 (D).

The examining veterinarian washed the lesions and administered antibiotics orally. Reexamination of the cat 2 weeks after initial evaluation did not indicate clinical improvement. Impression smears were made of the draining exudate, and the lesions were biopsied. Cytologic evaluation of the biopsy specimens indicated myriads of fungal organisms free and within macrophages and neutrophils (Fig 1B). The organisms were pleomorphic yeasts, with round, oval, and cigar-shaped forms 3 to 10 µm in diameter, consistent with Sporothrix schenkii (Fig 1C). Fungal culture and histologic evaluation of the biopsy specimens confirmed the diagnosis of sporotrichosis.

One week after the lesions were biopsied, the attending veterinarian developed an erythematous papule on the middle phalanx of the right middle finger (Fig 2).

Figure 2--Lesions on the finger of a woman with sporotrichosis acquired by handling a cat with the disease. Notice the large cavitated ulcer on the middle pahlanx of the right middle finger. (Courtesy of Dr. Donald Ditmars, Detroit, Mich).

The lesion progressed rapidly to an ulcerated nodule with associated painful lymphadenopathy of the right epitrochlear lymph nodes. Fungal culture of the ulcerated lesions yielded S schenkii. The cat and the veterinarian were administered potassium iodide orally. The lesions on the cat continued to expand, and the cat was euthanatized. During a 3-month course of therapy, the veterinarian's lesions healed completely.

A: Sporothrix schenkii is a dimorphic fungus that grows in a yeast form in body tissue and in culture at 37 C and grows as a filamentous fungus with fine septate branching hyphae at room temperature (30 C).^1-3 The organism is generally considered to be a saprophyte and grows naturally on vegetation or in soil, with a predilection for soils rich in organic matter or vegetable debris, especially sphagnum moss and tree bark.² Sporothrix schenkii has world-wide distribution and is found in temperate and tropical zones.^1,2

A: In human beings, sporotrichosis has been considered an occupational hazard of individuals who have direct contact with plants or soils. Infection is most often acquired via a penetrating injury⁴; however, there is some evidence that S schenkii can invade healthy and intact skin.^5,6 Although rare, inhalation of the organism can result in a pulmonic form of the disease.⁷ It has been hypothesized that cats most commonly become infected by dermal implantation when fighting unaffected cats that have contaminated organic debris on their claws⁸; however, infection has been identified in indoor cats whose only access to organic material was house plants and potting soil.⁹

With the exception of feline-to-human transmission, sporotrichosis is not generally considered contagious; however there are infrequent reports of the disease developing after bites, pecks, and stings inflicted by a variety of animals, birds, and insects.¹⁰

A: Sporotrichosis develops principally in sexually intact male cats that are allowed outdoors.⁸ Initial lesions of feline sporotrichosis may develop anywhere on the body, but they are most commonly found on the distal portion of the extremities, the head, or the base of the tail.^8,9,11

Lesions may appear as small, draining, puncture wounds and (in the early stages of the disease) are indistinguishable from bacterial abscesses or cellulitis associated with cat-inflicted scratches and bites; however, they fail to respond to antibiotic therapy. As the disease progresses, the lesions become nodular and ulcerated, and drain with a seropurulent exudate. Frequently, the ulcers become cavitated, and underlying muscle and bone may become exposed. The initial lesion may remain localized throughout the course of the disease (fixed cutaneous sporotrichosis) Often, the infection involves lymphatic vessels; when the distal portion of the extremities is involved initially, ulcerated nodules may develop along afferent lymphatic vessels (lymphocutaneous sporotrichosis). Cats also appear to spread the disease by licking and grooming affected sites, and multiple extremities and the face and ears often are involved secondarily. Experimentally, 50% of cats inoculated with S schenkii developed disseminated disease (ie, S schenkii was isolated from internal organs [multifocal disseminated sporotrichosis]).¹² Cats with the disseminated form of the disease often are febrile, depressed, and anorexic.^8,9,11

A: Histologically, the cutaneous lesions of feline sporotrichosis are characterized by a nodular to diffuse pyogranulomatous inflammatory reaction. Characteristically, feline sporotrichosis is associated with such large numbers of round, ovoid, and cigar-shaped fungal bodies that the diagnosis is easily established by examination of either Wright-stained impression smears of draining exudate or H&E-stained tissue sections (Fig 1D).^8,13,14 In our experience, cases of feline sporotrichosis in which organisms are difficult to identify histologically occur, but are rare.¹⁵ This is in contrast to the characteristic picture of the disease in infected dogs, horses, and human beings where organisms are notoriously difficult to identify histologically and the use of immunohistochemistry or fungal culture may be required to establish the diagnosis.^{4,7,13,14,16-20}

Cats with disseminated cutaneous involvement may have small numbers of organisms within multiple internal organs. Affected cats also may have intact organisms within their colonic feces, indicating that ingested organisms may be viable when they are defecated.⁹

A: The diagnosis of sporotrichosis is best established by obtaining a 6-mm punch biopsy specimen of the cutaneous lesions, and evaluating half the specimen mycologically (fungal culture) and half histologically. Fungal culture is the most definitive means of diagnosing sporotrichosis, but 10 to 14 days generally are required before the organism can be identified with certainty. Diagnosis by histologic assessment is more rapid; however, care must be taken not to confuse the Sporothrix organism with Candida spp, Histoplasma capsulatum, Trichosporon spp, or Leishmania spp.^{4,8,11,13,14,21} Cytologic assessment may be of value in establishing a preliminary diagnosis of feline sporotrichosis, and organisms are generally easy to find in impression smears of the exudate overlying the ulcerated nodules.⁸

A: The transmission of sporotrichosis from cats to people generally requires direct skin contact with the ulcerated and draining lesions or exudate of affected cats. Unlike infection associated with plant material, a penetrating injury is seldom reported, and any exposure to the draining and ulcerated lesions or exudate offers the potential for infection, perhaps by implantation through mildly irritated skin or through hypothesized ability of the organism to penetrate intact skin.^5,8,22-32 Because transmission requires contact with feline lesions, feline-to-human transmission predominantly involves individuals treating affected cats. Of 37 people who acquired sporotrichosis from cats, 23 were described as veterinarians or individuals under a veterinarian's supervision.^8,22-32 To date, all cat to human transmissions have resulted in either a localized cutaneous or lymphocutaneous form of the disease, and all lesions resolved with potassium iodide or ketoconazole therapy within 1 to 10 months.^8,22-32

A: Sporotrichosis should be suspected in any cat with suppurative or ulcerative skin lesions, especially when the lesions are refractory to antibiotic treatment. Precautions should be taken to minimize contact by individuals required to handle potentially affected cats while microbiologic and histologic confirmation is pending. Wearing gloves is strongly recommended when examining such cats. In one report,⁸ a veterinary technician who wore gloves during periods of contact with an affected cat initially developed lesions on the wrist where the cuffed edge of the glove ended. Therefore, even when gloves are worn, care should be taken when they are removed, and the hands and wrists should be washed and rinsed, preferably with an antiseptic solution with known antifungal activity, such as povidone iodine or chlorhexadine.³²

A: Potassium or sodium iodide, ketoconazole, and itraconazole have been cited in literature as options for treating feline sporotrichosis.^8,9,11,33,34 A supersaturated iodide solution is the traditional treatment for fixed cutaneous or lymphocutaneous forms of the disease (20% solution administered at dosage of 0.1 mg/kg of body weight, orally, every 24 hours).¹¹ However, cats are susceptible to iodide toxicosis; therefore, if vomiting or anorexia accompanies treatment, the dosage should be reduced or stopped until these signs regress. Treatment should then be continued at a lower dosage.

The imidazole, ketoconazole, also has been reported to be effective for treating cutaneous or lymphocutaneous sporotrichosis in cats experimentally infected with S schenkii.³³ In that study,³³ the skin lesions resolved clinically and results of cutaneous fungal culture became negative in response to ketoconazole (5 mg/kg, PO, q 24 h for 45 days); however this treatment regimen did not eradicate the organism from regional lymph nodes. Reports of successful treatment of naturally acquired feline sporotrichosis with ketoconazole are rare because adverse side effects, such as vomiting and diarrhea, often necessitate discontinuing its use in favor of iodide therapy.^8,34

Because side effects are common when ketoconazole is administered to cats, its use may be superseded by that of a second-generation imidazole, itraconazole. Itraconazole has a broader spectrum of action and is much better tolerated by cats than is ketoconazole.³⁵ The recommended dosage is 5 to 10 mg/kg, PO, q 12 or 24 h.⁹ Because itraconzole is packaged in 100-mg capsules, administering the correct dosage can be difficult. Moriello has recommended that the contents of capsules be opened and the capsules suspended in butter (see reference 9 for details). This not only makes giving the appropriate dose easier but, because itraconazole is lipophilic, improves its absorption. Treatment should be continued 30 days beyond clinical cure. Because it is potentially teratogenic, itraconzole should not be administered to pregnant queens.⁹ None of these drugs are approved for use in cats.

Feline sporotrichosis is different from sporotrichosis in other domestic species because of its relative ease of transmission from cats to people. The propensity of cats to transmit the infection to human beings may be attributable to the large number of organisms associated with the lesions in most affected cats. Such exposure does not require a penetrating injury for infection to develop. The unique biology of sporotrichosis in this species allows cats to act as an important source of human infection. In human beings, finding of numerous Sporothrix organisms in a lesional specimen is an indicator of localized or systemic immunosuppression.^36-38 This may not be true for cats. Experimental inoculation of S schenkii in healthy cats consistently induces infection with large numbers of organisms.³³ In addition, literature lacks an association with FeLV and feline immunodeficiency virus and the development of sporotrichosis in cats with large numbers of organisms.⁸

Although feline sporotrichosis is an uncommon disease, its ease of transmission to people makes it an important zoonosis. Veterinarians and their support personnel are most susceptible. All individuals reported to have acquired the disease from cats have responded favorably to treatment. In our experience, however, the disease may be quite disabling; individuals that acquired sporotrichosis from cats lost 2 to 16 weeks from work either because of the skin lesions or because of the side effects of iodide treatment. Cats appear to continuously shed fungal organisms in exudates from cutaneous lesions and in their feces, offering the potential for inhalation of the organism and the development of disseminated disease in an immunocompromised host that may share the same environment with an affected cat.

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23. Read SI, Sperling LC. Feline sporotrichosis: transmission to man. Arch Dermatol 1982;118:429-431.

24. Schiappacasse RH, Colville JM, Wong PK, et al. Sporotrichosis associated with an infected cat. Cutis 1985;36:268-270.

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26. Marques SA, Franco SR, de Camamrgo RM, et al. Esporotricose do gato domestico (Felis catus): transmissao humana. Rev Inst Med Trop Sao Paulo 1993;35:327-30.

27. Smilack JD. Zoonotic transmission of sporotrichosis (lett). Clin Infect Dis 1993;17:1075.

28. Naqvi SH, Becherer P, Gudipati S. Ketoconazole treatment of a family with zoonotic sporotrichosis. Scand J Infect Dis 1993;25:543-545.

29. Reed KD, Moore FM, Geiger GE, et al. Zoonotic transmission of sporotrichosis: case report and review. Clin Infect Dis 1993;16:384-387.

30. Zamri-Saad M, Salmiyah TS, Jasni S, et al. Feline sporotrichosis: an increasingly important zoonotic disease in Malaysia. Vet Rec 1990;127:480.

31. Caravalho J, Caldwell JB, Radford BL, et al. Feline-transmitted sporotrichosis in the Southwestern United States. West J Med 1991;154:462-465.

32. Rosser EJ, Jr. Sporotrichosis and public health. In: Kirk RW, ed. Current veterinary therapy X, small animal practice. Philadelphia: WB Saunders Co, 1989;633-634.

33. Raimer SS, Ewert A, MacDonald EM, et al. Ketoconazole therapy of experimentally induced sporotrichosis in cats: a preliminary study. Curr Ther Res Clin Exp 1983;33:670-680.

34. Burke MJ, Grauer GF, Macy DW. Successful treatment of cutaneolymphatic sporotrichosis in a cat with ketoconazole and sodium iodide. J Am Anim Hosp Assoc 1983;19542-547.

35. Mundell AC. New therapeutic agents in veterinary dermatology. Vet Clin North Am: Small Anim Pract 1990;20:1541-1556.

36. Bickley LK, Berman IJ, Hood AF. Fixed cutaneous sporotrichosis: unusual histopathology following intralesional corticosteroid administration. J Am Acad Dermatol 1985;12:1007-1012.

38. Fitzpatrick JE, Eubanks S. Acquired immunodeficiency syndrome presenting as disseminated cutaneous sporotrichosis. Int J Dermatol 1988;27:406-407.