Yellow Fungus Disease in Bearded Dragons: Care Guide

lizard with darkened patch of skin and lesion caused by yellow fungus disease in bearded dragons

Yellow fungus disease in bearded dragons is often picked up on by pet owners when their bearded dragons skin is yellow, brown or black in patches. The name ‘yellow fungus disease’ comes from the yellow – brown discoloration of infected skin.

Yellow fungus disease in bearded dragons (also known as CANV – Chrysosporium anamorph of Nannizziopsis vriesii) is a fairly newly defined pathogen implicated in a fungal infection.

CANV belongs to a group of fungi which are keratinophilic – meaning that it likes to grow on keratin (the stuff that scales are made of). These infections are becoming more common over the last several years, originally identified in North America, then into Europe, and now as far reaching as Australia.

Over this time, the causative agent has undergone several name changes as microbiologists’ study deeper into the disease. Yellow fungus disease is fairly well documented now in several species of reptiles. It is particularly devastating to bearded dragons, often being fatal.

What Causes Yellow Fungus Disease in Bearded Dragons

Yellow fungus disease, or CANV, is a primary pathogen. This means that it can act alone in causing disease. Yellow fungus disease (YFD) gets its name from the yellow to yellowish brown skin color it causes.

The fungus can affect perfectly healthy bearded dragons at any time. However, there are some predisposing factors to consider.

The contributors or causes of yellow fungus disease in bearded dragons include:

  • Poor husbandry.
  • Stress.
  • Overcrowded conditions.
  • Unsanitary conditions, poor cleaning program.
  • Inadequate nutrition.
  • Dermatitis.
  • Open skin lesions including trauma, bite or scratch wounds, even an injured toenail are significant risks, as they provide an entry-point for CANV. The skin barrier is particularly important.

It is believed that an asymptomatic carrier state exists where a seemingly healthy lizard can be the source of infection.

The beginning stage of yellow fungus disease in bearded dragons starts when it enters through the skin, feeding on keratin within the scales. As the infection matures, it may spread over the skin, resulting in more lesions, randomly dispersed over the skin. Given time, the infection will spread deeper, invading the fat and muscle layers, eventually affecting lungs, liver and spleen.

These individuals are dealing with systemic fungal disease, and are very sick, they carry a very poor prognosis. Unfortunately, the extent of an infection may not be readily identifiable by external observation. Many deeper infections are diagnosed via postmortem examination.

image for post on yellow fungus disease in Bearded Dragons shows a bearded dragon held in a hand with hyperpigmentation over one third of the body starting from tail
One of the symptoms of yellow fungus disease in bearded dragons is hyperpigmentation of the skin (darkening of the skin). This bearded dragon shows hyperpigmentation on the last third of the body near the tail (caudal 1/3 of body). Photo courtesy of Charlotte

Symptoms of Yellow Fungus Disease in Bearded Dragons

The most obvious symptoms of yellow fungus disease in bearded dragons is the skin turning yellow and progresses towards black over time. Other symptoms include:

  • Abnormal shedding: Often one of the first signs. Affected areas look like an incomplete shed; affected individuals may shed more often. Crusting of the skin. Often beginning with only a few scales – crusts may present as a yellow or tan colour. Any area of the body may be affected.
  • Swelling of the infected area: Swelling of the immediate area of infection is possible, but may affect a whole limb.
  • Ulceration or sores: The outer layer of skin may slough off resulting in a raw, exposed area
  • Blunting of scales: Scar tissue will look flattened, with notable loss of normal scale architecture.
  • Hyperpigmentation, or darkening of scales. In time, the yellow – tan areas may appear darkened and black, indicating chronicity of infection
  • Hyperkeratosis, or roughening of scales: As the inflammation persists, the skin may gain a roughened appearance
  • Necrotic patches. Skin may become necrotic (non viable, or dead) It is important that these lesions be debrided – in some cases that means limb amputations.
  • Anorexia: Affected animals may lose appetite as the infection internalizes.
  • Stunted growth: As with any systemic disease, sub-optimal growth may be an easy indicator that something is wrong.
  • Pathologic fractures. Deep infections can spread beyond the skin and to the bone – particularly around the mouth and limbs. Infected bone can be very brittle, and will break easiest – even with gentle “routine” manipulation.
  • Lethargy: As the disease progresses, general signs of being unthrifty will present.
  • Death: CANV kills bearded dragons.
blunted scales yellow fungus bearded dragon
Blunting of the scales on the caudal aspect of the right side of the head caused by yellow fungus (CANV). Photo courtesy of Charlotte

How to Treat Yellow Fungus Disease in Bearded Dragons

Treatment of yellow fungus disease in bearded dragons at home is not sufficient to manage the disease. When you notice something wrong with your bearded dragon, get veterinary help quickly. Delays can result in unnecessary suffering and increase the costs of treatment.

The early lesions of yellow fungus disease do not always look significant, and this may be the reason that bearded dragons are often brought in late in the course of the disease. Because of this, further testing may be required to assess the overall health status of the animal. These tests may include bloodwork, or x-rays.

Treating yellow fungus disease in bearded dragons takes several weeks. Although the fungal infection may reach “remission” it is unlikely to ever to be fully cleared. Treatment may provide comfort and quality of life to affected animals.

Treatment of yellow fungus disease in bearded dragons requires a combination of medications and improvements to their living conditions. Providing the right enclosure (especially size for the right gradient), properly set up heating and lighting, cleanliness and hydration are all keys in the effectiveness of treatment.

To treat yellow fungus disease in bearded dragons:

  1. Call your vet. You cannot tackle yellow fungus diease on your own, medical support is required.
  2. Things you can do at home while you wait for veterinary support:
    Isolate your bearded dragon, yellow fungus disease (CANV) is a highly contagious.
    Chlorhexidine soap or Nolvasan may be useful to begin treating the infection topically. Both Chlorhexidine and Nolvasan are typically available from chemists and are anti-fungal plus anti-bacterial. Apply the treatments past the infected areas, wash off after half an hour.
    Minimize environmental stress. No unnecessary handling, movement near the cage or any other activity that could lead to stress.
    Keep the enclosure clean. Cleanliness is extremely important to keep infection under control.
  3. Give your vet the full history of what has occured and what you have done about it so far.
    Unfortunately, yellow fungus disease cannot be diagnosed by physical exam alone, as the lesions often look similar to other common problems (trauma, bacterial skin infections, and burns).
    A skin biopsy may be needed which may require sedation of your bearded dragon. Ideally, this sample is sent to a lab for a fungal culture (to grow out the causative agent), histopathology (examination of the sample under the microscope), and PCR or polymerase chain reaction (a highly specific DNA sequencing test).
    Although recommended, extensive testing is not always possible, and a presumptive diagnosis may be made on a case by case basis.
  4. Treatment involves the use of a systemic (oral or injectable) antifungal drug. The infection is likely more than just skin deep. Because of this, topical medication alone is not enough. Three drugs have been studied including:
    • ketoconazole,
    • itraconazole, and
    • voriconazole.
      Systemic antifungals can be harmful to the liver of bearded dragons and tend to be fairly costly. Of these three drugs, studies have shown that voriconazole may be the safest.
      A combination of oral antifungal medication along with creams or ointments can be helpful. Just using creams on the outside isn’t enough to treat yellow fungus disease. The oral medication is the main treatment.
      Some examples of common creams or ointments used to treat yellow fungus disease are:
    • terbinafine,
    • chlorhexidine, and
    • silver sulfadiazine.
  5. Removing the damaged or nectrotic (dead) tissue, also known as debridement, can be beneficial as well. If your vet recommends debridement then it is expected that they will show you how to do that without causing harm or unnecessary pain.
    Yellow fungus disease will cause nectrotic tissue, which is tissue that is not viable. The tissue has lost its’ blood supply, it is dead, and therefore, systemic drugs have no way to penetrate this tissue. The fungus will reside within and feed on this dead tissue.

Will my Bearded Dragon Die from Yellow Fungus Disease (CANV)?

At this time, the vast majority of bearded dragons afflicted by yellow fungus disease will die from the condition, or side effects from the medication used.

Death usually occurs within a few months, but varies greatly between individuals. One report of four bearded dragons infected with CANV resulted in euthanasia within 6 months. Prognosis will change drastically depending on how severely the individual is affected.

ulceration from yellow fungus in bearded dragon
Ulceration of right side of tail base – notice how the architecture of the scales is obliterated. A yellow- tan color can be appreciated. Photo courtesy of Charlotte

Yellow Fungus Disease is Highly Contagious

Yellow fungus disease (CANV) is a highly contagious disease easily passed between individuals in the same household. The fungus is passed in several ways:

  • Direct contact between individuals,
  • Through the air,
  • On surfaces, or on the skin and clothes of a handler.

This means you need to put in place quarantine practices to ensure the disease is not spread between reptiles.

Can I Catch Yellow Fungus From My Bearded Dragon?

CANV is not believed to be zoonotic. It is unlikely you can catch yellow fungus from your bearded dragon however immunocompromised individuals may be susceptible to Nannizziopsis spp.

Cases of CANV in humans have been found to be caused by a different specifies of Nannizziopsis than the one found in reptiles.

Consult with your doctor if you are unsure or if you are likely to come in contact with immunocompromised individuals.

How do you Get Rid of CANV in Bearded Dragons?

Although recent studies are promising, it is not yet possible to fully and reliably eradicate CANV. Once an animal has been infected, it cannot be cleared.

As with many conditions, treatment proves very difficult, and often unrewarding, so we tend to focus on prevention.

  • Quarantine new additions to your bearded dragon population.
  • Avoid undue stress and handling.
  • Ensure cleanly environment. It is vital to reduce the fungal load in the environment as quickly as possible and keep it down which is done by cleaning. This includes replacing substrates.
  • Proper diet.
  • Proper lighting, temperature and humidity are essential. Ensure your setup is right, see the post on setting up your lighting and heating or the humidity post. Low ambient temperatures have been connected with infection.
  • Frequent hand washing will help prevent transmission. At this time, CANV is not believed to be zoonotic, and thus poses no risk to the human population, although proper hand washing is always recommended.

References

  1. Abarca ML, Martorell J, Castella G, Ramis A, Cabanes FJ (2009) Dermatomycosis in a pet inland bearded dragon (Pogona vitticeps) caused by a Chrysosporium species related to Nannizziopsis vriesii. Vet Dermatol 20: 295–299.
  2. Bowman MR, Paré JA, Sigler L, Naeser JP, Sladky KK, et al. (2007) Deep fungal dermatitis in three inland bearded dragons (Pogona vitticeps) caused by Chrysosporium anamorph of Nannizziopsis vriesii. Med Mycol 45: 371–376.
  3. Cabañes FJ, Sutton DA, Guarro J (2014) Chrysosporium-Related Fungi and Reptiles: A Fatal Attraction. PLoS Pathog 10(10): e1004367.
  4. Mitchell MA, Walden MR (2013) Chrysosporium anamorph Nannizziopsis vriesii: an emerging fungal pathogen of captive and wild reptiles. Vet Clin North Am Exot Anim Pract 16: 659–668.
  5. Van Waeyenberghe L, Baert K, Pasmans F, van Rooij P, Hellebuyck T, et al. (2010) Voriconazole, a safe alternative for treating infections caused by the Chrysosporium anamorph of Nannizziopsis vriesii in bearded dragons (Pogona vitticeps). Med Mycol 48: 880–885.
  6. WHA Fact Sheet: Yellow fungus and related diseases in Australian reptiles. Wildlife Health Australia. December 2018

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