Systemic mycoses review urges broader suspicion in dogs and cats
Bottom line
A new review in Veterinary Clinics of North America: Small Animal Practice puts systemic mycoses back in focus for companion animal clinicians, arguing that fungal disease in dogs and cats remains both clinically important and easy to miss because presentations are so variable and often overlap with other inflammatory conditions. The article, by Andrew S. Hanzlicek, centers on the practical challenge of diagnosing infections such as histoplasmosis, blastomycosis, coccidioidomycosis, and cryptococcosis, especially when organisms are sparse in pathology samples and no single test serves as a gold standard. Broader veterinary references support that point: definitive diagnosis often depends on combining cytology or histopathology with culture, serology, antigen testing, imaging, and, in some cases, PCR. (merckvetmanual.com)
Why it matters: For veterinary professionals, the takeaway is less about a new therapy and more about diagnostic discipline. Systemic fungal infections can affect apparently healthy dogs and cats, may mimic neoplasia or immune-mediated disease, and often require prolonged antifungal treatment once identified. Antigen testing can be especially useful in some diseases, including blastomycosis and histoplasmosis, but cross-reactivity and imperfect sensitivity mean results need to be interpreted in clinical context rather than in isolation. Geography and exposure history still matter, too: coccidioidomycosis remains tied to arid regions, while histoplasmosis and blastomycosis have their own endemic patterns. (merckvetmanual.com)
What to watch: Expect continued attention on better fungal diagnostics, especially how antigen assays, molecular testing, and multimodal workflows can shorten time to diagnosis in general practice and referral settings. (pubmed.ncbi.nlm.nih.gov)
Key facts
- Article topic
- Systemic mycoses in dogs and cats
- Journal
- Veterinary Clinics of North America: Small Animal Practice
- Author
- Andrew S. Hanzlicek
- Key diseases
- Histoplasmosis, blastomycosis, coccidioidomycosis, and cryptococcosis
- Main diagnostic challenge
- Signs overlap with inflammatory and neoplastic disease, and organisms may be sparse in pathology samples
- No gold standard
- No single test serves as a gold standard
- Diagnostic approach
- Cytology or histopathology, culture, serology, antigen testing, imaging, and sometimes PCR
- Clinical takeaway
- Diagnosis often requires a layered, multimodal approach
- Geography
- Coccidioidomycosis is tied to arid regions
Systemic fungal disease is back on the clinical radar in companion animal medicine, with a new review by Andrew S. Hanzlicek in Veterinary Clinics of North America: Small Animal Practice highlighting just how difficult these infections can be to recognize and confirm in dogs and cats. Based on the available abstract and supporting literature, the article frames systemic mycoses as globally relevant, diagnostically challenging infections whose signs often overlap with other inflammatory or neoplastic conditions. (merckvetmanual.com)
That emphasis fits a long-standing problem in small animal practice. Primary systemic mycoses, including histoplasmosis, blastomycosis, coccidioidomycosis, and cryptococcosis, can infect immunocompetent animals, and their distribution is shaped by geography, environment, and exposure history rather than by classic contagion between patients. Older epidemiologic work in dogs, along with more recent human surveillance data, reinforces that these diseases have recognizable endemic footprints and seasonal or regional patterns, even if those patterns are evolving. (pubmed.ncbi.nlm.nih.gov)
The core clinical message is that diagnosis usually requires a layered approach. Merck’s veterinary references note that while clinical findings and serology may be suggestive, definitive diagnosis typically relies on microscopic identification, culture, or PCR, and antigen titers can be useful in selected mycoses. For histoplasmosis, urine antigen ELISA is generally the most sensitive substrate, though cross-reactivity with other fungi, particularly Blastomyces, is a known limitation. For blastomycosis, urine or serum antigen testing outperforms antibody testing for diagnosis and can help monitor remission, but it still shouldn’t replace clinical examination and imaging. For coccidioidomycosis, serology remains more useful than antigen detection in many cases, because antigen assays have shown limited sensitivity. (merckvetmanual.com)
That matters because fungal organisms are not always easy to find on routine samples. The source synopsis notes that organisms may be sparse in pathology specimens, which helps explain why clinicians often need to combine routine lab work, imaging, cytology, histopathology, and targeted infectious disease testing rather than waiting for a single definitive result. Hanzlicek’s prior work has also touched fungal diagnostics and treatment monitoring, including reduced fluconazole susceptibility in feline histoplasmosis, underscoring that even once these infections are identified, management can be prolonged and clinically nuanced. (pubmed.ncbi.nlm.nih.gov)
Direct expert commentary on this specific review was limited in open web sources, but the broader specialist consensus is consistent: fungal testing is most valuable when paired with signalment, travel history, imaging findings, and tissue-based diagnostics. Reviews and reference materials aimed at clinicians repeatedly caution against overinterpreting a positive antigen result without considering cross-reactivity, and against dismissing disease after a negative test when suspicion remains high. (merckvetmanual.com)
Why it matters: For veterinary teams, this is a reminder to keep systemic mycoses on the differential list, especially in patients with chronic respiratory, gastrointestinal, ocular, dermatologic, neurologic, or multisystem disease that doesn’t fit neatly into more common categories. It also reinforces the value of asking detailed exposure and travel questions of the pet parent, because endemic fungal disease may present far from the site of exposure. In practice, the review’s message supports earlier multimodal testing and, when appropriate, earlier consultation with internal medicine, pathology, or infectious disease experts rather than repeated empiric treatment for presumed inflammatory disease. (vetmed.oregonstate.edu)
There are also operational implications. Cases often require long treatment courses, serial monitoring, and careful communication with pet parents about cost, prognosis, and the limits of any one diagnostic assay. As fungal diagnostics continue to evolve, including broader interest in PCR and other advanced detection methods, clinicians may gain faster tools, but interpretation will still depend on pretest probability and specimen quality. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next step is whether this review changes frontline workups by prompting earlier fungal testing in compatible cases, and whether newer molecular and antigen-based methods can improve sensitivity without adding more ambiguity around cross-reactivity and false reassurance from negative results. (pubmed.ncbi.nlm.nih.gov)