Canine Sporotricosis: Clinic, Epidemiology, Diagnosis and Treatment ()
1. Introduction
Sporotrichosis is an infectious disease caused by fungi belonging to the genus Sporotrix. The disease affects humans and animals, being described in several species, including felines, canines, horses, pigs, cattle, camels, and primates [1].
Sporotrichosis was initially described by Schenck in 1898, in the United States of America (USA), in a 36-year-old human patient with an abscess in the finger and nodular lymphangitis in the forearm. The isolated fungus was studied by the mycologist Erwin F. Smith, who concluded that it belongs to the genus Sporotrichum [2]. However, it was only in 1962, by morphological differentiation, that Carmichael determined that the correct agent nomenclature was Sporothrix chenckii, and in 2007, after phenotypic and genotypic analysis of several isolates obtained in different countries, a division of the agent Sporothrix chenckii was proposed in a complex, composed of different pathogenic species [3] [4].
Canine sporotrichosis is an uncommon disease and current knowledge is derived from a few case reports and case series [5]. Some canine cases have been documented in Italy [6], the USA [7], and Brazil [8] [9]. Thus, the objectives of the present study were to describe the epidemiological, clinical, laboratory and therapeutic aspects of canine sporotrichosis.
2. Etiology and Epidemiology
The species of the Sporothrix chenckii complex belong to the Fungi Kingdom, Ascomycota Division, Class Pyrenomycetes, Order Ophiostomatales, Family Ophiostomataceae [10]. They are dimorphic fungi, which in the saprophyte phase, at 25˚C have filamentous colonies and in parasitism at 35˚C - 37˚C they present colonies in the form of oval single-celled yeasts [11]. The Sporotrix chenkii complex is composed of six species: S. chenkii sensu strictu, S. globosa, S brasiliensis, S. mexicana, S. luriei [4].
Several factors have been associated with the development of sporotrichosis in humans and animals: 1) the ability of fungi of the genus Sporothrix to support and grow at the body temperature of the hosts (thermotolerance); 2) activity of several proteolytic enzymes that facilitate the adhesion and penetration of fungi in the cells and tissues of the host; 3) alkalinization of the microenvironment; 4) ability to adhere to endothelial and epithelial cells, as well as to the components of the extracellular matrix; 5) production of ergosterol peroxide; and 6) production of melanin [11] [12].
Fungi of the genus Sporothrix live in the soil, along plant edges and in regions with favorable climatic conditions, such as regions of temperate and humid tropical climates [13]. Infection can occur through injuries caused by vegetation that are contaminated with fungi or when in contact with contaminated cats, by scratching, biting or exudates from the lesions. Infection by cats is the most common form of transmission of sporotrichosis to dogs. The disease can affect animals of all ages and usually occurs as isolated cases [8].
In Brazil, cases of canine sporotrichosis are more frequent in the southeastern region of the country, mainly in the city of Rio de Janeiro associated with feline sporotrichosis. The disease in cats is considered epidemic in Rio de Janeiro [14].
3. Clinical and Laboratory Findings
Canines infected with fungi of the genus Sporotrix usually have ulcerated or nodular skin lesions, which can drain purulent or seropurulent material. The lesions are usually located on the head, ear, chest, and limb, but any region of the body can be affected [8].
A rare and widespread form of osteoarticular sporotrichosis has been mentioned in the literature [8].
In addition to cutaneous signs, some animals may also present systemic clinical signs such as: lethargy, immunosuppression, depression, prostration, hypertension, anorexia, vomiting, weight loss, dyspnea, nasal discharge, generalized lymphadenomegaly and sneezing [1] [8] [9].
The main laboratory changes in dogs with sporotrichosis are shown in Figure 1 [8] [15].
In general, no changes in the biochemical profile and urinalysis of dogs with sporotrichosis are observed [15].
4. Diagnostic
The diagnosis of sporotrichosis is usually made by isolating Sporothrix spp. from aspirated material, swabs or biopsy specimens obtained from active lesions. Occasionally, the diagnosis is obtained by the demonstration of suggestive fungal elements in cytological or histological sections [8] [16].
Cytologic findings are usually low, and it can be observed degenerate neutrophils, macrophages, small mature lymphocytes, and eosinophils. Low numbers of intracellular (within neutrophils and macrophages) and extracellular, pleomorphic, cigar-to-ovoid shaped organisms (approximately 3 × 9 μm) consistent with Sporothrix may be observed [17].
Histologic examination may reveal foci of granulomatous inflammation and rare pleomorphic PAS-staining organisms [18].
Immunohistochemistry, ELISA and PCR can also be used as an auxiliary method for the diagnosis of sporotrichosis in dogs. [19] [20] [21].
5. Diferencial Diagnoses
Cryptococcus neoformans, Histoplasma capsulatum, Leishmania spp., Toxoplasma gondii, Neospora caninum, Sarcocystis spp. and Blastomyces dermatitidis are the main differential diagnoses of canine sporotrichosis [22] [23].
6. Treatment and Control
The treatment and its duration are individual in terms of the severity of the
![]()
Figure 1. Frequency of haematologycal abnormalities [8] [15].
lesions and the patient's response to it, so it is necessary to be uninterrupted so that there is no recurrence of the condition [24].
Azole antifungals are used, in this case imidazoles (miconazole and clotrimazole) and triazoles (itraconazole and fluconazole), sodium and potassium iodides 20%, terbinafine, amphotericin B, local thermotherapy and surgical removal of lesions [25]. Itraconazole is the antifungal agent of choice for treatment, and it is considered superior in comparison to other antifungal drugs, and it is very often used in both cases of human involvement and in animals. Itraconazole therapy is carried out for a period of 60 days and should be maintained for approximately 30 days after clinical healing [4] [26]. Treatment is considered effective and can be completed only when the lesions are fully healed, and the results of the fungal cultures are negative [27].
For the control, awareness and understanding of the tutors about the disease, emphasizing the fact that this is an important zoonosis are necessary. Special care must also be taken, such as the use of gloves for handling animals that have suspected, confirmed lesions, and are undergoing treatment for sporotrichosis. Still, through research it is indicated to perform the castration of male dogs, reducing fights, exits, demarcation of territory, which would considerably minimize the risk of infection [28].
7. Conclusion
In contrast to sporotrichosis involving cats, sporotrichosis in dogs is considered to be of minimal zoonotic importance. Nevertheless, in regions where feline sporotrichosis is epidemic dogs with skin lesions should be treated carefully due to the risks of contamination. Moreover, infection with Sporothrix spp. should be considered in dogs with persistent cutaneous or subcutaneous nodular lesions, especially if they fail to respond to treatment. A history of exposure to environments or catfight should raise the index of suspicion. Azole antifungals are the drugs of choice for the treatment of the disease.
Acknowledgements
This work was supported by Fundação de Amparo à Pesquisa e Inovação do Espírito Santo (FAPES), and was financed in part by the Coordenação de Aperfei- çoamento de Pessoal de Nível Superior (CAPES), Brasil-Finance code 001.