For anyone who runs a cat sanctuary—or even a home with cats who have escaped feline infectious peritonitis (FIP)—gum disease is often the silent complication nobody warns you about. At the Gardens of St. Gertrude, our 92-cat sanctuary in Cyprus, we've seen FIP survivors battle intractable gingivitis long after the acute infection subsides. Their gums bleed, they stop eating, their teeth deteriorate. Antibiotics help for a while. Then the problem returns.
The reason, I believe, lies not in the teeth themselves, but in the microbial ecosystem. FIP-associated gingivitis isn't simply a bacterial infection you can bomb with amoxicillin. It's a polymicrobial biofilm—a sticky, orchestrated community of bacteria and fungi working together to evade immune clearance. And if you want to break that community apart, you need to think ecologically.
Last year, I published a paper proposing that a combination of itraconazole (an antifungal) and lactoferrin (an iron-binding immune protein) can disrupt this biofilm in ways that neither drug alone achieves. The mechanism is counterintuitive, elegant, and entirely consistent with what I've observed in our cats. Let me walk you through it.
The Polymicrobial Trap
FIP itself is caused by a coronavirus. But once it damages the intestinal epithelium and peritoneum, secondary infections take hold—including opportunistic fungi like Candida albicans. These Candida cells don't just colonize the mouth; they actively protect other pathogens from immune detection.
In particular, Candida albicans creates a microenvironment that shields the gram-negative bacterium Porphyromonas gingivalis—the canonical cause of gingivitis. In the presence of Candida, P. gingivalis becomes nearly invisible to neutrophils. The bacteria produce potent proteases and hijack iron and zinc from the host, causing the gum inflammation we see clinically.
Here's the problem: treat only the P. gingivalis with antibiotics, and Candida remains. The fungus persists, re-enables the bacteria, and your cat is back to bleeding gums in weeks.
Conversely, if you treat only the Candida, you might assume the bacterial problem is solved. But P. gingivalis has already burrowed deep into biofilm. A brief window of vulnerability isn't enough.
Drug Repurposing Without Patent Bias
This is where the ecological blind spot in pharmacology becomes painfully obvious.
Itraconazole is not approved for FIP-associated gingivitis. It's an antifungal—it has no direct mechanism against P. gingivalis. From a traditional pharmaceutical perspective, it shouldn't work. But mechanistic plausibility and patent incentive are not the same as biological reality.
What itraconazole does is remove Candida from the local biofilm environment. This exposes P. gingivalis to the cat's innate immune system. The bacterium can no longer hide.
But that's only half the story.
Nutritional Immunity and Metallomics
Once P. gingivalis loses its fungal shield, lactoferrin takes over.
Lactoferrin is an iron-binding glycoprotein secreted by neutrophils in response to inflammation. It has been used in veterinary practice for decades—it's in many commercial colostrum supplements, for instance—but its role in bacterial eradication is often underappreciated.
When P. gingivalis is exposed to the immune system (thanks to Candida removal), neutrophils can now reach it and release lactoferrin. Lactoferrin sequesters iron in the local biofilm environment. P. gingivalis needs iron to produce virulence factors and proteases. Without bioavailable iron, the bacteria become metabolically crippled.
This is nutritional immunity in action—the host's ancient strategy of starving pathogens of essential metals. And it ties directly to microbial metallomics: the desperate struggle pathogens wage to acquire and hoard trace metals.
P. gingivalis uses siderophores (iron-scavenging molecules) to steal iron from the host. But lactoferrin outcompetes these siderophores. Once iron is bound to lactoferrin, P. gingivalis cannot access it. The bacteria's gum-destroying proteases shut down. Virulence collapses.
Why This Works in Practice
In our sanctuary, cats receiving the itraconazole + lactoferrin combination showed sustained gum healing over 4–6 weeks. Bleeding stopped. Appetite returned. Importantly, relapse was rare—a stark contrast to antibiotic monotherapy, which often requires repeated courses.
The reason is that we're not fighting a single pathogen; we're dismantling an ecosystem. Itraconazole removes the ecological enabler (Candida). Lactoferrin imposes a nutritional blockade on the remaining pathogen (P. gingivalis). Together, they create conditions the biofilm cannot survive.
This is not magic. It's drug repurposing grounded in host–pathogen ecology.
A Word on Zinc
I should mention: some vets are tempted to add zinc supplementation to support immune function. I advise against this in the context of active FIP-associated gingivitis. Zinc, like iron, can be exploited by P. gingivalis and Candida. During active infection, nutritional immunity works best when metals are restricted, not supplemented. Once the biofilm is cleared and the cat's microbiome has stabilized, zinc support may be appropriate—but that's a different conversation.
Clinical Implications
If you're managing FIP survivors with persistent gingivitis, the take-home is simple: don't treat the bacterial infection in isolation. Address the polymicrobial biofilm. Itraconazole removes the fungal shield. Lactoferrin imposes nutritional siege.
This approach may seem radical to vets trained in single-agent, single-pathogen pharmacology. But the cats respond better. And in sanctuary medicine, where every cat matters, that's what counts.
The work I published on this (Pendergrass, 2025) is available on Zenodo (DOI: 10.5281/zenodo.18085985). It's open-access—no paywall, no corporate gating. The microbiome revolution belongs in the clinic, not behind a subscription barrier.
Closing Thought
Running the Gardens means caring for cats at every stage of illness. Some arrive with active FIP; others are in remission. A few seem to bounce back fully. But the gum disease—it follows them, quietly. I'm glad we found a way to interrupt it. And I hope this framework—ecological thinking, drug repurposing, nutritional immunity—helps other vets and caretakers do the same.
Your cats deserve better than syndrome management. They deserve ecology-informed care.
References
Pendergrass, K. (2025). Itraconazole and lactoferrin for FIP-associated gingivitis in cats: A perspective. Zenodo. https://doi.org/10.5281/zenodo.18085985