Yellow Skin Disease in Bearded Dragons

Bearded Dragon lizards (Pogona vitticeps) have become extremely popular pets in recent years, perhaps the most popular and suitable reptile pet for beginning reptile keepers. And for good reason as they are relatively hardy, easy to cater for (as far as reptiles go) and have outgoing, engaging personalities akin to our more common mammal pets. They do, like other reptiles, require specialist knowledge and equipment to keep healthy and well however, and often the cost of providing appropriate lodgings and husbandry far exceeds to value of the animal itself. Because they are such common reptile pets, and also many beginner keepers start out with this species I frequently see them in clinic for a range of conditions, many of which can be attributed at least partly to shortcomings in their husbandry (how they are kept and managed) or nutrition. They can suffer from various infectious diseases caused by bacterial infections, various parasites and less commonly fungal infections.

Necrotic ulcer left after sloughing of lesion, with topical ointment

Necrotic ulcer left after sloughing of lesion, with topical ointment

One of the worrying trends being observed worldwide, but noticeably in the past several years in the UK is the spread of a specific fungal pathogen that can cause severe skin infections or fungal dermatitis and ultimately death in Bearded Dragons primarily, but also some other reptile species. The pathogen responsible is a fungal organism with the rather long-winded scientific name of Chrysosporium Anamorph of Nanniziopsis vriesii (CANV) which is colloquially known amongst hobbyists as ‘Yellow Skin Disease’ of Bearded Dragons. This is an aggressive fungus which invades the superficial and deep layers of the skin and causes discolouration of the skin, necrotic lesions which slough off revealing sensitive ulcerated tissues underneath the scales and diffuse painful subcutaneous swelling and inflammation. In severe cases the hyphae of the fungus, which are microscopic root like filaments, can extend deeper into the animals body cavities and internal organs often causing marked pathology and eventually death.

Beardie with ulcerating, hyperkeratotic necrotic lesions, skin swelling & discoloration

Beardie with ulcerating, hyperkeratotic necrotic lesions, skin swelling & discoloration

 

 

Transmission of the fungus responsible is thought to be from direct contamination with the fungal agent encountered in the environment, and is easily spread throughout reptile collections and other facilities housing large numbers of animals by keepers and on equipment. The incubation period from the time infection occurs to the development of visible signs can be several weeks to over a month so it is often difficult to pinpoint the exact source of infection, especially in newly acquired animals. Suboptimal husbandry conditions such as low temperatures and poor hygiene practices are often responsible for predisposing animals to this disease. However many well cared for and otherwise healthy animals can become infected if exposed to the pathogen also.

After infection, the early signs of disease usually present as dry, crusty, hyperkeratotic lesions and discoloration of the skin which can lead to patches of retained skin after shedding. Excessive or more frequent shedding is common at this stage of disease also. These lesions generally progress over several weeks to months and become necrotic and exudative meaning the skin starts to die and release infectious discharge. Wet, scabby lesions form on the surface of the skin and eventually slough off or can be lifted off when cleaned to reveal pustular discharge underneath and ulcerated inflamed soft tissue devoid of the superficial skin layers or scales. These ulcers are obviously very painful and prone to secondary bacterial infections. Once the disease has advanced this far it can be quite difficult to treat successfully. Recovery and regeneration of new skin takes a considerable period of time, and the animal is often left with extensive scar tissue if it survives. Lesions are commonly found on or near the mouth or head but can be found anywhere on the body. Other diseases which may be confused for this condition include bacterial dermatitis, stomatitis, thermal burns and indeed other fungal skin infections. Diagnosis is made based on clinical signs, appearance, and testing skin samples or tissue biopsy for the organism itself using PCR, microscopy or culture techniques.

Exudative, crusting lesion typical of Yellow Skin Disease of Bearded Dragons

Exudative, crusting lesion typical of Yellow Skin Disease of Bearded Dragons

 

 

Treatment is multimodal and involves the use of an oral antifungal drug called Itraconazole which needs to be given every day for 4-6 weeks in most cases. Antibiotics are sometimes used also to treat or guard against secondary bacterial infections. Topical cleaning with chlorhexidine is recommended as well as the application of topical antifungal agents such as miconazole or F10 ointment. Topical agents alone are not indicated for a successful outcome however, as it appears that most success is achieved using systemic antifungal treatment with oral itraconazole at the correct dose rate. For this reason it is crucial if you have an animal you think might be affected to seek the advice of an experienced reptile veterinarian. The disadvantage of using this drug is that it can have severe side effects with long term use however, especially with regard to liver function and particularly in already debilitated animals. It is crucial therefore that affected lizards are treated early, appropriately and that supportive care is given in the form of supplemental feeding and hydration if necessary. Monitoring of liver function during treatment may be necessary in some cases, which requires blood sampling. Aggressive surgical debridement of lesions is sometimes warranted also to reduce the presence of the fungal agent and aid in treatment. I have treated several suspected and confirmed cases of this disease in Bearded Dragons and one suspected case in a chameleon. Sadly not all of them have survived. In two cases where a single limb was affected I amputated the affected limb and the Beardie went on to live a very happy life.

If caught early, this disease can be treated successfully. It is critical to prevent the spread of the organism to other reptiles so isolation of the affected animal and great care to prevent mechanical transmission on owners hands, clothes or equipment is recommended. Rigorous cleaning and disinfection of cages, furnishings and equipment is also crucial in limiting spread of the organism or re-infection as well as discarding all contaminated substrate or porous materials from the affected animals vivarium. The disease is not zoonotic meaning it does not readily transmit to humans as it is primarily a reptile pathogen. However there have been a few reports of CANV isolated from severely immunocompromised human patients so sensible hygiene precautions that should be implemented with any ill pet need to be taken.