Pathogenic fungi establish infection in apparently normal hosts, and such diseases as histoplasmosis, coccidioidomycosis, blastomycosis, and cryptococcosis are regarded as primary systemic mycoses. Opportunistic fungi are more likely to establish infection in an immunosuppressed host, but this is not a prerequisite to infection in animals. Prolonged administration of antimicrobials or immunosuppressive agents appears to increase the likelihood of infection by the opportunistic fungi that cause diseases such as aspergillosis and candidiasis, which may be focal or systemic.
Clinical findings, gross lesions and serology are often suggestive of systemic mycoses; however, definitive diagnosis requires microscopic identification, culture of the organism, or PCR assay. Identification of the fungus and the tissue reaction via microscopic examination of exudates and biopsy material is adequate for diagnosis of histoplasmosis Histoplasmosis in Animals Histoplasmosis is a chronic, noncontagious, disseminated, granulomatous disease of humans and other animals due to the dimorphic fungus Histoplasma capsulatum var capsulatum. The... read more 
, cryptococcosis Cryptococcosis in Animals Cryptococcosis is a systemic fungal disease that often affects the respiratory tract (especially the nasal cavity), CNS, eyes, and skin. The causal fungi exist in tissues in an encapsulated... read more 
, blastomycosis Blastomycosis in Animals Blastomycosis is a multifocal fungal infection due to the dimorphic fungi Blastomyces spp. The fungi are often found in soil or decomposing organic matter, such as leaves. Infection is... read more 
, coccidioidomycosis Coccidioidomycosis in Animals Coccidioidomycosis (valley fever) is a dustborne, noncontagious infection due to Coccidioides spp fungi. These fungi form mycelial mats in shallow arid soil; the mycelium fragments form... read more 
, and sporotrichosis Sporotrichosis in Animals Sporotrichosis is a sporadic, chronic, granulomatous disease of humans and various domestic and laboratory animals due to Sporothrix spp. Infection usually results from direct inoculation... read more 
. Other diseases, such as candidiasis Candidiasis in Animals Candidiasis is a usually localized mucocutaneous disease due to species of the yeastlike fungus Candida, most commonly C albicans. It is distributed worldwide in a variety of animals... read more 
, aspergillosis Aspergillosis in Animals Aspergillosis is a sporadic fungal infection due to several environmentally ubiquitous Aspergillus spp. A fumigatus is believed to be the most common; however, multiple other species... read more 
, phaeohyphomycosis Phaeohyphomycosis in Animals Phaeohyphomycosis refers to chronic cutaneous, subcutaneous, mucosal, cerebral, or systemic infection due to pigmented (dematiaceous) septate molds. Fungi in this category are saprophytic, widely... read more 
, hyalohyphomycosis Phaeohyphomycosis in Animals Phaeohyphomycosis refers to chronic cutaneous, subcutaneous, mucosal, cerebral, or systemic infection due to pigmented (dematiaceous) septate molds. Fungi in this category are saprophytic, widely... read more , and oomycosis Oomycosis in Animals Oomycosis is due to pathogens in the class Oomycetes. These organisms are not true fungi but are aquatic pathogens, predominantly of plants, that are found in warm, still, fresh water. Oomycetes... read more 
(pythiosis and lagenidiosis), require more than microscopic evaluation for a definitive diagnosis.
Some fungi are commonly found as normal flora as well as contaminants of cultures; thus, tissue invasion and reaction must be demonstrated for the culture isolation to be considered noteworthy. Serologic testing may be useful for diagnosis (and prognosis) of some mycotic diseases such as coccidioidomycosis, pythiosis, and lagenidiosis. Antigen titers have proved useful for cryptococcosis, histoplasmosis, and blastomycosis.
For treatment,seediscussions of specific systemic mycoses below and under pharmacotherapeutics of the integumentary system Overview of Systemic Pharmacotherapeutics of the Integumentary System in Animals Also see Principles of Topical Therapy in Animals. Drugs that may be used in the integumentary system fall into several therapeutic categories, such as antimicrobials ( antibacterials and antifungals)... read more .
