Dermatomycosis associated with Nannizziopsis arthrosporioides in a breeding colony of gecko (Correlophus ciliatus and Rhacodactylus auriculatus).

This paper reports the first documented fatal outbreak of *Nannizziopsis arthrosporioides*-associated dermatomycosis in a breeding colony of *Correlophus ciliatus* and *Rhacodactylus auriculatus* geckos, which occurred following the introduction of an infected individual from overseas.

The Gist

Imagine a reptile breeding facility as a bustling, high-end apartment complex for geckos. These geckos, specifically the Crested Gecko (Correlophus ciliatus) and the New Caledonian Gecko (Rhacodactylus auriculatus), live in their own private, climate-controlled units. They are fed a special diet, kept at the perfect temperature, and generally live happy, healthy lives.

Then, a new tenant moves in.

The New Neighbor and the Invisible Invader

One day, a male Crested Gecko arrives from overseas. He seems fine at first, but he's carrying an invisible stowaway: a microscopic fungus called Nannizziopsis arthrosporioides. Think of this fungus not just as a germ, but as a tiny, aggressive termite that loves to eat the "wood" of the gecko's skin (specifically the keratin).

Within a month, the new gecko gets sick and dies. His skin turns dark, thick, and crusty, looking like a map of a burnt landscape. But here's the scary part: he didn't just get sick because he was weak. He passed the "termite" to his neighbors.

Even though the other geckos lived in separate boxes, they shared the same air, the same feeding spoons, and the same caretakers. The fungus hitched a ride on these shared items, jumping from the new arrival to the existing residents. It was like a ghost spreading through a building via the ventilation system.

The Outbreak: A Skin-Eating Plague

Soon, the infection spreads.

• The First Wave: Two geckos who had "indirect contact" with the new arrival get sick. Their skin turns dark red or black, their toes become hard and plate-like (like a car tire losing its tread), and they die quickly.
• The Second Wave: Five months later, four more geckos get sick. These ones don't just have skin issues; they get diarrhea, lose weight rapidly, and their toe pads rot away.

In total, seven geckos died. The vets and scientists were like detectives arriving at a crime scene. They took samples and looked under the microscope.

What the Microscope Revealed

The investigation revealed a terrifying scene inside the geckos' bodies:

1. The Fungal Invasion: The "termite" fungus had completely eaten away the outer layer of the skin. It wasn't just sitting on the surface; it had drilled deep into the flesh, spreading like roots of an invasive weed through the soil.
2. The Bacterial Backup: Because the skin's defense wall was destroyed, bacteria (like Pseudomonas and E. faecalis) moved in like looters in an empty house, causing secondary infections.
3. The Smoking Gun: The scientists grew the fungus in a lab and compared its DNA to a global database. It was a perfect match for Nannizziopsis arthrosporioides.

Why This Matters

This paper is a big deal for three reasons:

1. It's a New Victim: While this fungus was known to hurt other reptiles (like snakes and turtles), this is the first time it has been confirmed as a killer in these specific types of geckos. It's like discovering a new species of shark that only eats a specific type of fish nobody thought was at risk.
2. It's Highly Contagious: The fungus spread easily through shared equipment, even when the geckos were kept apart. This is a warning to pet owners and breeders: clean your tools, or the whole colony could be at risk.
3. It Might Jump to Humans: The paper notes that this fungus has recently been found in humans with weak immune systems. Since these geckos are popular pets traded globally, there is a risk that this "termite" could jump from reptiles to people. It's a reminder that the line between pet diseases and human health is thinner than we think.

The Takeaway

The story of these geckos is a cautionary tale about the dangers of moving animals around the world. A single new pet can bring a microscopic "army" that can wipe out an entire colony. The scientists are now calling for better ways to diagnose and treat this specific fungus before it becomes a bigger problem for both reptiles and people.

In short: Don't let the new guy bring the "skin-eating termites" into your house.

Technical Summary

1. Problem Statement

Fungal infections in reptiles, particularly those caused by the Nannizziopsis genus (formerly known as Chrysosporium anamorph of Nannizziopsis vriesii or CANV), are emerging threats to biodiversity and captive reptile populations. While Nannizziopsis species are known to cause dermatomycosis in various reptiles, the specific pathogenicity and infection status of Nannizziopsis arthrosporioides remain poorly understood, with only five prior reptile species reported. This study addresses the lack of data regarding N. arthrosporioides in geckos by investigating a lethal outbreak in a breeding colony of two Diplodactylid species: the Crested Gecko (Correlophus ciliatus) and the Gold Dust Gecko (Rhacodactylus auriculatus).

2. Methodology

The study employed a comprehensive pathological, microbiological, and molecular approach to investigate an outbreak involving seven deceased geckos (five C. ciliatus and two R. auriculatus) in a facility housing approximately 30 individuals.

• Epidemiological Investigation: The team traced the outbreak timeline, noting the introduction of an imported male C. ciliatus (Case 1) in May 2024, followed by deaths in indirect contacts over the subsequent months. Husbandry conditions (temperature 26–28°C, humidity 40–50%, individual housing) were reviewed and found to be standard and stable.
• Gross and Histopathological Examination: All seven geckos underwent complete necropsy. Tissues were fixed in 10% neutral-buffered formalin, embedded in paraffin, sectioned, and stained with Hematoxylin and Eosin (H&E) and Grocott's methenamine silver stain to visualize fungal elements.
• Mycological Culture and Morphology: Skin lesions from five cases were cultured on Potato Dextrose Agar (PDA). Colony morphology and micromorphology (conidia and arthroconidia) were observed under microscopy.
• Molecular Identification: DNA was extracted from fungal isolates (Cases 2 and 5). The Internal Transcribed Spacer (ITS) and partial actin gene regions were amplified via PCR, sequenced, and compared against the NCBI database using BLAST to confirm species identity.
• Bacteriological Analysis: Bacterial cultures were performed on skin lesions from Cases 1–3 to identify secondary opportunistic infections.

3. Key Results

• Clinical Presentation:
  • Cases 1–3: Exhibited severe, extensive skin lesions characterized by map-like discoloration (dark red/blackish-green), thickened skin, and cellulitis on the abdominal trunk and toe pads. Case 2 showed visceral involvement (fibrin deposition, hepatic degeneration).
  • Cases 4–7: Developed later, presenting with toe pad discoloration, loss of subdigital lamellae, severe emaciation, diarrhea, melena, and necrotic enteritis.
• Histopathology:
  • All seven cases showed consistent findings: complete absence of the epidermis, extensive necrosis of the dermis and subcutaneous tissue, and layered fungal proliferation with hyphae extending deep into tissues.
  • Fungal hyphae were uniform in width with right-angled or obtuse branching. Inflammatory cell infiltration was notably mild despite extensive necrosis.
  • In Case 2, fungal hyphae were also found in visceral organs (pancreas, liver), indicating systemic dissemination.
• Microbiological Findings:
  • Fungal Identification: Two isolates (FC-7673 from Case 2 and FC-7731 from Case 5) were identified as Nannizziopsis arthrosporioides.
    • Morphology: Slow-growing colonies (5–6 cm in 1 month at 25°C), powdery, white with a yellowish tinge. Produced thallic conidia and cylindrical arthroconidia (15–28 μm).
    • Genetics: ITS and actin sequences showed >98% identity to the type strain of N. arthrosporioides (UTHSC R4263).
  • Bacterial Co-infection: Mixed bacterial infections were identified in severe cases, including Pseudomonas aeruginosa, Providencia rettgeri, Stenotrophomonas maltophilia, and Enterococcus faecalis. These were deemed secondary opportunistic infections.
• Transmission: The outbreak was traced to horizontal transmission via indirect contact (shared feeding spoons and enclosure access) following the introduction of an infected imported gecko. No other geckos in the facility without contact to the new animal were affected.

4. Key Contributions

• First Report in Geckos: This is the first documented case of a fatal outbreak of Nannizziopsis arthrosporioides specifically in geckos (C. ciliatus and R. auriculatus).
• Pathogenicity Characterization: The study demonstrates that N. arthrosporioides is highly pathogenic in Diplodactylid geckos, capable of causing rapid, lethal systemic infections and severe necrotic dermatitis, challenging the previous notion that its pathogenicity was limited or unknown in this host group.
• Transmission Dynamics: It highlights the risk of indirect transmission via fomites (feeding equipment) in breeding colonies, even when animals are housed individually.
• Zoonotic Potential: The paper reinforces the zoonotic potential of Nannizziopsis species, noting that while N. arthrosporioides was previously thought to be reptile-specific, recent human cases suggest a broader host range, necessitating caution in handling infected reptiles.

5. Significance

• Veterinary and Conservation Impact: The findings underscore the critical need for strict quarantine protocols for imported reptiles to prevent the introduction of novel fungal pathogens into breeding colonies. The high mortality rate and rapid spread observed suggest that N. arthrosporioides poses a significant threat to captive reptile populations.
• Diagnostic Advancement: The study provides detailed morphological and genetic markers for N. arthrosporioides, aiding in the rapid diagnosis of similar outbreaks.
• Public Health: Given the international trade in reptiles and the potential for zoonotic transmission, this report calls for public health risk assessments and the development of rapid diagnostic methods and effective treatments for Nannizziopsis infections, which currently lack established therapeutic protocols.
• Pathogenesis Insight: The observation of mild inflammation despite severe necrosis suggests that N. arthrosporioides may possess mechanisms to evade or suppress the host immune response, leading to rapid tissue destruction and secondary bacterial sepsis.