Yellow Fungus in Bearded Dragons: Signs, Diagnosis and Prognosis

What it is

Yellow fungus disease is a serious and often fatal fungal skin infection in pet bearded dragons.¹ It is caused by fungi in the genus Nannizziopsis, chiefly N. guarroi.¹² Older sources call it CANV, short for Chrysosporium anamorph of Nannizziopsis vriesii, a name from before the fungi were reclassified.²³

The infection starts in the outer skin and can spread into the deeper skin, muscle and, rarely, bone.²

Signs to watch for

• Yellow to brown, or gray, crusted skin¹³
• Thickened or swollen scales, and rough or flaky patches¹
• Skin that looks dirty but does not clean off¹
• Patches that start small and spread over time¹³
• Painful or sensitive areas¹
• Less often, lumps that slough off and leave open sores²
• Weight loss, poor appetite and sunken eyes³

Not every yellow patch is yellow fungus. Other organisms can cause similar yellow discoloration, so testing matters.²

How vets diagnose it

Diagnosis may involve skin scraping or removing scales, a biopsy, a fungal culture and PCR testing.¹ A definitive diagnosis needs PCR with sequencing.² Because the disease can progress quickly, treatment may start before results come back.¹

Treatment and outlook

Treatment is usually aggressive and long. Options include surgically removing infected tissue, oral antifungal medication for weeks to months, topical treatment for secondary infections, and strict disinfection of the enclosure.¹

The outlook is often guarded to grave. Recurrence is common, advanced cases may not respond, and treatment is costly and not always successful. Early treatment improves survival.¹

ReptiFiles is blunter: it says there is no cure, and that most affected dragons die within 12 to 18 months of diagnosis.³

Stopping it spreading

Yellow fungus spreads between reptiles.¹ Washington State University advises:¹

• Isolate any infected reptile at once
• Handle infected reptiles last, and clean your hands and tools afterwards
• Disinfect enclosures and supplies with a 10% bleach solution, with at least two minutes of contact time
• Do not reuse an enclosure that has housed an affected dragon
• Quarantine every new reptile before it meets your others

Poor husbandry increases the risk.¹ ReptiFiles lists poor hygiene, low temperatures, poor nutrition and living with other reptiles among the factors that weaken a dragon’s defenses.³