The most common fungal disease is captive reptiles is commonly called yellow fungus disease (YFD) because it causes a yellow to yellow-brown skin color. This disease is also often called CANV after what was thought to be the fungus that caused it, Chrysosporium anamorph of Nannizziopsis vriesii. It is now known that the most common cause of YFD in captive bearded dragons (Pogona vitticeps) is Nannizziopsis guarroi. Fungal disease should be among the list of potential causes of disease for any reptile with skin problems.
Bearded dragons with YFD often shows up as a small yellow to brown crust on the surface of a few scales that in time gets larger. Other crusts may appear elsewhere on the body in a random fashion and eventually turn dark and thickened or rough.
Occasionally, an early sign of YFD is a bad shed that leaves behind dull scales with a roughened appearance. In some dragons, it may result in a shedding storm where the dragon seems to be shedding all the time. As the disease progresses, it may become an internal infection and lead to poor appetite, weight loss, and death. YFD is contagious and can spread from one dragon to another both by direct contact between animals and through the air. Young bearded dragons seem to more vulnerable to YFD than adults. If you have a YFD positive dragon, any cage mate needs to be watched closely for signs of disease.
YFD is associated with stress, often seen in dragons kept under crowded unsanitary conditions. It’s often seen in those dragons which are raised in groups, shipped in groups, or displayed for sale in groups. It is also thought that injured toenails and minor bite wounds associated with dragons under crowded conditions results in damage to the skin which provides an opening for the fungus to infect the dragon.
Sanitation may be compromised with high populations of lizards in the same cage, which in turn increases the likelihood of a lizard being exposed to the fungus. Furthermore, crowding causes stress that results in suppressed immune response, so a lizard may not be able to fight even a low level of the fungus. But because the YFD is a primary pathogen (it can cause disease even in healthy reptiles with good husbandry) any dragon can get it.
In this article we are concentrating on YFD in bearded dragons but many species of reptiles have been diagnosed with the same or similar fungal diseases including: It is important to understand that there are many different species of fungus that can cause disease in reptiles, although you certainly don’t have to memorize them, which include:
- Nine species of Nannizziopsis associated fungal disease seen in chameleons, geckos (like leopard geckos), tegus, iguanas and crocodiles.
- Paranannizziopsis includes four species that infect snakes, lizards and tuataras.
- Ophidiomyces, with the single species Ophidiomyces ophiodiicola, is only associated with terrestrial or semiaquatic snakes.
- Nannizziopsi guarroi is the main causal agent of yellow fungus disease in captive bearded dragons (Pogona vitticeps), and O. ophiodiicola is the cause of mycoses in captive snakes and of snake fungal disease, an emergent global threat to populations of endangered wild snakes.
Your veterinarian will start by taking a thorough medical history and give a physical examination. YFD cannot be distinguished from a variety of other diseases just by looking, including other fungal diseases, bacterial diseases, some viruses and things like burns. Your veterinarian will likely recommend some tests to determine if your dragon has YFD.
A biopsy (taking a small tissue sample) is needed to confirm a diagnosis of YFD. Your veterinarian will anesthetize your dragon for a short period of time and get a few biopsy samples that will be looked at under the microscope; some of the sample may be submitted for a PCR test and some for culture to grow the fungus to determine what type it is.
A firm diagnosis of YFD, however, can only be established when biopsies collected from the dragon are shown to be the same fungus that is cultured or indicated by PCR testing.
A veterinarian may suggest bloodwork, X-rays and/or ultrasound to better assess your reptile’s health and rule out a serious internal illness caused by the fungus infecting the dragon’s deeper tissues or organs.
YFD is contagious to other dragons and so the infected dragon should be kept in a separate cage from all other reptiles in the collection. Your veterinarian will discuss how to prevent transmission from the infected dragon to others.
Any areas of the skin with YFD changes (called lesions) should be cleaned up or removed in a process called debridement because the dead skin contains fungus that is out of reach of the antifungal medication given to the dragon. Systemic antifungal drugs - those given by injection or orally - are always indicated because a YFD infection usually goes deeper than just the skin.
Your veterinarian will suggest treatment with antifungal drugs for your infected dragon and may choose one or a combination of the following drugs: Voriconazole, amphotericin B, terbinafine, and/or itraconazole. He may recommend treating any skin biopsy sites or lesions with an antibiotic cream or iodine once or twice a day.
If you have a dragon with YFD, any cage mate needs to be watched closely for signs of disease. You should consider separating the cage mates to reduce the risk of cross-infection from the infected one to the seemingly healthy one. Another reason to separate them is to reduce competition between them. Sometimes there are subtle social interactions that create stress and immunosuppression, and make cage mates more susceptible to infections. Other exposed reptiles should have thorough veterinary examinations and any skin problems should be checked for YFD.
Any new dragon to the collection that arrives with a skin problem or that develops a skin problem while in quarantine should not be placed in the main collection released until checked for YFD.
Proper Hygiene and Sanitation
Proper sanitation and hygiene are key risk reducers. As with other infectious diseases, a reptile is better able to resist an infection if it is fed the proper diet and is given excellent husbandry (i.e., a thermal gradient, appropriate lighting, the right range of humidity, hiding spots). Avoid purchasing reptiles kept under crowded conditions, particularly where there are obvious skin lesions on other specimens sharing the same container.
Prognosis and Outcome
YFD is often fatal and the treatment is usually for a long period of time. The best chance for a successful cure is when the disease is diagnosed and treated by your veterinarian early on in the disease process.
The fungus that causes YFD can only grow at temperatures lower than that of the human body and so the potential for infection from your dragon to you is very low or non-existent.