Chromoblastomycosis: A Century-Old Fungal Disease Where Science Outpaces Care

Chromoblastomycosis is one of medicine’s most stubborn paradoxes. First described more than a century ago, this chronic fungal infection of the skin and subcutaneous tissues has been the subject of steady scientific progress, from the discovery of new causative species to the development of molecular diagnostic tools and more active antifungal drugs. Yet patients in the rural tropics, where the disease overwhelmingly occurs, still receive diagnoses based on the same low-cost microscopic methods used decades ago, and their treatment still rests on observational experience rather than randomized trials. A new synthesis published in PLOS Neglected Tropical Diseases by Daniel Wagner C. L. Santos, Dallas J. Smith, Vania Aparecida Vicente and colleagues lays out this disconnect in stark terms, arguing that chromoblastomycosis exemplifies a neglected tropical disease in which advances in basic science have failed to translate into better outcomes at the clinic or the public health level.

The disease itself begins deceptively small. Chromoblastomycosis is an implantation mycosis, meaning the fungi responsible enter the body through traumatic inoculation, typically when a thorn, splinter, or plant fragment carrying pigmented, soil-dwelling fungi pierces the skin of an agricultural worker. Over months and years, the infection progresses through verrucous, nodular, and plaque-like lesions that can spread along lymphatic pathways, and in advanced cases causes fibrosis, lymphedema, and disfiguring scarring. Although mortality is comparatively low, morbidity is considerable and durable: lesions can persist for decades, secondary bacterial infection is common, and squamous cell carcinoma can arise in long-standing scars. The condition predominantly affects rural populations in tropical and subtropical regions, particularly impoverished people who work barefoot or with exposed skin in contact with vegetation and soil.

Perhaps the most striking finding in the recent literature is how much the epidemiological picture has expanded. Historically associated with impoverished rural settings in Latin America, Africa, and Asia, chromoblastomycosis is now increasingly reported in both endemic and non-endemic areas, including high-income countries. Some of these cases reflect travel and migration, but others point to genuine local transmission in regions previously thought to be at low risk. This shifting landscape suggests that the true burden of disease is underrecognized. The authors emphasize a sobering metric gap: even basic measures of population impact, such as disability-adjusted life years, remain undefined for chromoblastomycosis, a deficiency recently highlighted by global health initiatives that have called for better quantification of fungal disease burden. Without such metrics, the disease struggles to compete for attention, funding, and drug development against conditions whose costs are more visible on public health dashboards.

On the biological side, however, the past two decades have been remarkably productive. Molecular taxonomy, built on DNA sequencing of fungal markers and whole genomes, has substantially reshaped our understanding of the etiological agents. The traditional picture cast the disease as caused by a handful of pigmented fungi, most prominently Fonsecaea pedrosoi and Cladophialophora carrionii. Sequencing studies have since revealed far greater biodiversity, with novel genera and species identified among clinical isolates, particularly from immunocompromised hosts. These discoveries matter clinically as well as academically, because different species can differ in virulence, geographic distribution, and response to antifungal therapy, and because fungi once lumped together under old names may behave differently in the human host. The recognition of new agents of disease in patients with weakened immunity has reshaped our understanding of host-pathogen interactions in this infection.

Diagnostics have advanced in parallel, at least in the laboratory. Polymerase chain reaction-based assays and genomic approaches now allow species-level identification that is far more precise than morphology, which has always been tricky with dematiaceous fungi that share overlapping microscopic features. Histopathology, culture, and the direct visualization of the pathognomonic muriform cells, the thick-walled, dark-brown, dividing fungal structures found in tissue, remain the backbone of diagnosis in practice. Molecular tools have improved species-level identification considerably, but the synthesis is blunt about their limitations: availability remains largely restricted to reference centers. In the endemic settings where most patients live, diagnosis continues to rely on low-cost conventional methods. The authors make a counterintuitive but important point here: precisely because those conventional methods are inexpensive, and despite imperfect sensitivity, they should be more widely incorporated into public health screening and active case-finding strategies rather than waiting for technology transfer that may never arrive.

Therapeutics present a similarly mixed picture. Extended-spectrum triazoles, such as itraconazole and the newer agents posaconazole and voriconazole, together with terbinafine, an allylamine antifungal that inhibits fungal squalene epoxidase, have shown the most consistent activity against the causative fungi. Treatment traditionally combines these systemic antifungals with physical approaches, including surgical excision for smaller lesions and cryotherapy with liquid nitrogen for accessible plaques, and combinations of drugs and techniques are often used for refractory disease. Yet even the best outcomes come slowly: therapy frequently spans months to years, relapse is common, and advanced lesions may never resolve fully. The evidence underpinning these choices is thin. Antifungal susceptibility testing lacks clear clinical correlation, meaning laboratory minimum inhibitory concentrations do not reliably predict whether an individual patient will respond to a given drug. Treatment decisions remain largely based on observational studies and expert experience, in the absence of randomized controlled trials.

Into this therapeutic landscape, the authors highlight emerging adjunctive immunomodulatory strategies, with imiquimod standing out as the most promising. Imiquimod is a topical immune response modifier that activates toll-like receptor 7, effectively recruiting the host’s own innate and adaptive immune machinery against the pathogen. This is an appealing logic for chromoblastomycosis, since the muriform cells that persist in tissue are notoriously resistant to direct antifungal killing, and host immunity appears central to controlling the infection. Used alongside systemic antifungals, imiquimod has shown encouraging results in case series, particularly for patients whose lesions respond poorly to drugs alone. Such approaches represent a conceptual shift: rather than simply escalating antifungal exposure, clinicians may be able to tilt the host-pathogen balance toward clearance. Still, the evidence base remains small, and the authors are careful to frame these strategies as emerging alternatives rather than established standards.

The deeper problem the synthesis identifies is structural. New technologies have not been incorporated into broader clinical and public health interventions. Molecular species identification improves taxonomies in reference laboratories in Europe and North America while a farmer in Madagascar or Brazil waits weeks for a culture result and then faces years of therapy with drugs that may be unaffordable or unavailable locally. Novel agents with better activity profiles exist on paper, but no pharmaceutical industry incentive drives the trials that would establish optimal regimens for a disease affecting dispersed, poor, rural populations. The absence of randomized controlled trials is not an accident of oversight but a predictable consequence of neglect: chromoblastomycosis lacks the defined burden metrics, the surveillance infrastructure, and the market forces that normally attract trial investment. The result is a field rich in descriptive biology and poor in implementation evidence.

The authors argue that closing this gap requires a deliberate rebalancing of priorities. Strengthening public health strategies means training primary care workers in endemic regions to recognize early lesions, since disease caught at the verrucous or nodular stage is far more treatable than disease caught after years of misdiagnosis as cutaneous leishmaniasis, tuberculosis, or carcinoma. Expanding access to simple and effective diagnostic tools means deploying the muriform-cell smear and culture more aggressively rather than reserving confirmation for molecular methods. Prioritizing implementation-focused research means studying how to deliver existing therapy to real patients, what drug combinations and durations work in programmatic settings, and what the true costs of disability actually are. International efforts to elevate fungal diseases within the neglected tropical disease agenda offer a policy opening, and the recent attention to undefined DALYs suggests momentum for better burden estimates.

Chromoblastomycosis, in the end, is a test case for the entire neglected tropical disease enterprise. The science has not stood still: new species have been named, genomes sequenced, susceptibility profiles catalogued, and immune-based adjuncts explored. But a century after the disease was first described, the measure of progress is not the number of novel taxa in the literature. It is whether the agricultural worker with a scaly foot lesion is diagnosed earlier, treated faster, and cured more completely. The synthesis by Santos, Smith, Vicente and their colleagues makes clear that on those measures, the gap between laboratory and clinic remains wide and persistent. Bridging it will require investment not in more discovery for its own sake, but in the unglamorous machinery of screening, surveillance, accessible diagnostics, and trials designed for the settings where the disease actually lives. Until then, chromoblastomycosis will remain a textbook example of how scientific knowledge can flourish while patients’ realities stand still.

Subject of Research: The gap between molecular research advances and clinical practice in chromoblastomycosis

Article Title: From molecular advances to limited clinical impact: The persistent gap in chromoblastomycosis

Article References: Santos, D. W. C. L., Smith, D. J., Vicente, V. A., Lustosa, B. P. R., & Azevedo, C. D. M. P. E. S. D. (2026). From molecular advances to limited clinical impact: The persistent gap in chromoblastomycosis. PLOS Neglected Tropical Diseases, 20(10), e0014801. https://doi.org/10.1371/journal.pntd.0014801

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014801

Keywords: chromoblastomycosis, neglected tropical diseases, medical mycology, molecular diagnostics, antifungal therapy, terbinafine, triazoles, imiquimod, fungal taxonomy, public health, rural health, PLOS Neglected Tropical Diseases