TREATMENT FOR CHYTRID FUNGUS 

Donald K. Nichols
Elaine W. Lamirande
Dept. of Pathology
Smithsonian Institute

We have used topical application of itraconazole (Sporanox, Janssen Pharmaceutica, Inc., Titusville, New Jersey, USA) to successfully treat cutaneous chytridiomycosis in blue-and-yellow poison dart frogs (Dendrobates tinctorius). In Experiment 1, juvenile frogs were experimentally exposed to Batrachochytrium dendrobatidis, a newly described fatal chytridiomycete (Chytrid) fungus.

Excessive shedding of skin was seen in all frogs 14 days post exposure. Chytrids were present in the pieces of shed skin and in skin imprints made from the frogs. A 1% suspension of itraconazole was diluted to a final concentration of 0.01% itraconazole using 0.6% saline as the dilutant. One group of frogs was immersed in this suspension for 5 min daily for II consecutive days. After the last treatment, the frogs were moved to clean cages and closely monitored. Another group of frogs served as positive controls and was not treated; they all died within 35 days of initial Chytrid exposure. Clinical signs resolved completely in the itraconazole treated frogs. These frogs were euthanised 43 days post exposure (38 days after the last treatment), and there was no histological evidence of Chytrid infection.

In Experiment 2, sub-adult and adult D. tinctorius were experimentally exposed to B. dendrobatidis and Chytrid infections were proven through microscopic examination of skin imprints and pieces of shed skin. These frogs were treated with 0.01% itraconazole baths for 8 consecutive days and then moved to clean cages. Subsequent skin imprints from these frogs have been negative for Chytrids and the frogs remain healthy 8 months later. 

Donald K, Nichols and Elaine W. Lamirande, Department of Pathology, National Zoological Park, Smithsonian Institution, 3000 Connecticut Avenue NW, Washington, DC 20008 USA Email: nichols@nzp.si.edu

Mr Nichols added the following: - I am sure you can get itraconazole in Europe. It is rather expensive when purchased in bulk but the tiny amounts needed to treat frogs makes the cost of treatment more reasonable. In the US, it can only be obtained with a doctor's (MD or vet) prescription. I am sure that other related drugs in the imidazole group would also work and might be less expensive. No matter which drug you use, the thing to beware of is what other supposedly "inert" compounds are present; these can often have adverse effects on frogs.

And a response from one of our Veterinary members Bruce MacLean, Bird & Exotic Animal Vet Servs, Kelperland Veterinary Centre, Ascot Road, Touchen End, Berks. SL6 3LA

Whilst I do not have experience of using systemic antifungal treatments in frogs, I have used topical antiseptics in salamanders and newts. It is true that amphibians may be sensitive to non-specific components in drug preparations, as well as the drugs themselves, so preparation of the drug can make a difference.

In terms of treatment options, I have been unable to find anything specifically British with regard to treatment of Chytrid fungi, and if presented with an outbreak my initial temptation would be to try different treatments on different affected frog/groups of frogs. I would see if anyone else had used any treatment with success -though I am not aware of anyone at present, but if presented with a case I would contact other vets with an interest in this area.

Considering the available medications, and the fact that the fungus appears to affect mainly keratinised areas so should be reasonably susceptible to external treatments, I would probably include antiseptic treatments such as benzalkonium chloride baths (2 mg/l for 60 min daily this has been reportedly successful in Basidiobolus spp fungal infection) and fish antifungal treatments.  As a general rule it is preferable to use drugs which are used in fish, as these are most likely to be safe for amphibians.

Various specific antifungal treatments are available in this country, including itraconazole. However, as far as I am aware, itraconazole is only available as a human preparation, in capsule form, so there may be fillers or other compounds in it. I would probably try it (unless someone told me otherwise), based on the results reported, but only on 1 or 2 frogs initially. Of the other antifungal drugs - I have sources for an oral dose for ketoconazole (10 mg/kg daily), available as a tablet in this country, which would be worth considering on larger amphibians. There are others available but I can find no reference to their use in amphibians, and as a rule they are relatively toxic drugs.

From the point of view of quarantine, the antiseptic or fish treatment baths, with the currently available treatments may well be worth considering.