Study links neutrophil ratios to fungal skin infections in dogs: full analysis

A new Veterinary Dermatology case-control study is sharpening the clinical picture around a rare but serious complication of immunosuppressive therapy in dogs: cutaneous opportunistic invasive fungal infections during ciclosporin treatment for immune-mediated disease. In a matched retrospective analysis, researchers found that higher neutrophil count, neutrophil-to-lymphocyte ratio, and neutrophil-to-monocyte ratio were significantly associated with infection, while other host factors and treatment variables were not. The paper was published online ahead of print on April 27, 2026. (pubmed.ncbi.nlm.nih.gov)

That finding builds on a small but important body of literature linking ciclosporin-based immunosuppression to unusual skin infections in dogs. A 2017 study from Texas A&M reported opportunistic invasive cutaneous fungal infections in dogs treated for immune-mediated disease, noting that management often required prolonged antifungal therapy and careful adjustment of immunosuppression. Earlier reports also described cutaneous nocardiosis in dogs receiving ciclosporin, including one case with elevated trough drug levels during combination therapy with ketoconazole. (pmc.ncbi.nlm.nih.gov)

In the new study, investigators reviewed client-owned dogs treated with ciclosporin, with or without systemic glucocorticoids, for a range of immune-mediated diseases. Cases were dogs that developed cutaneous opportunistic invasive fungal infections during treatment, and controls were matched by both underlying immune-mediated disease and duration of ciclosporin exposure. The authors retrospectively collected signalment, clinical history, and laboratory data, including CBC-derived ratios, acute-phase proteins, globulins, and immunoglobulin concentrations. Among the variables examined, only neutrophil count, NLR, and NMR were significantly associated with infection. (pubmed.ncbi.nlm.nih.gov)

Just as important, the study did not identify significant associations between infection and broader host characteristics or therapeutic regimen. That includes the use of glucocorticoids in this dataset, though the authors said further work is needed to clarify the role of steroid co-administration. That nuance matters because prior educational and review material has cautioned that combining ciclosporin with systemic corticosteroids may increase the risk of opportunistic infections, particularly in heavily immunosuppressed dogs. (pubmed.ncbi.nlm.nih.gov)

Direct outside commentary on this specific paper appears limited so far, but the broader dermatology literature is consistent on one point: opportunistic infections under ciclosporin are uncommon, yet clinically meaningful when they occur. Reviews of ciclosporin use in veterinary dermatology have generally described the drug as having a favorable long-term safety profile in many canine patients, especially at labeled doses, while case reports and retrospective series continue to remind clinicians that unusual bacterial, fungal, and protozoal infections can emerge under immunosuppression. (research.ed.ac.uk)

Why it matters: For veterinary professionals, this study may be most useful not because it proves causation, but because it suggests a practical monitoring angle. CBC-derived inflammatory ratios are inexpensive, already available in routine practice, and may help flag dogs on ciclosporin who deserve closer dermatologic surveillance. In practice, that could mean paying more attention to new nodules, draining tracts, plaques, or nonhealing skin lesions in immunosuppressed dogs, even when the drug protocol itself doesn’t seem unusually aggressive. The study also reinforces that absence of a clear regimen signal shouldn’t reassure clinicians too much if the bloodwork and skin findings are moving in the wrong direction. (pubmed.ncbi.nlm.nih.gov)

There are also limits worth keeping in mind. The study included only eight affected dogs and 20 controls, so it should be viewed as hypothesis-generating rather than definitive. Even so, for clinicians balancing disease control against infectious risk in dogs on ciclosporin, the paper offers a more specific question to ask during follow-up: not just whether the patient is immunosuppressed, but whether neutrophil-driven inflammatory markers are trending upward as skin lesions emerge. (pubmed.ncbi.nlm.nih.gov)

What to watch: The next step will be prospective validation in larger cohorts, especially to determine whether NLR and NMR can reliably guide monitoring, earlier diagnostics, or treatment adjustments in dogs receiving ciclosporin alone or in combination with glucocorticoids. (pubmed.ncbi.nlm.nih.gov)