Mucor amphibiorum: a death worse than chytrid?

Well, we thought so until we starting receiving frogs ill with chytrid. Chytrid is still pretty miserable for a frog!

Mucor amphibiorum doesn't have a common name but you could call it mucormycosis which is a little easier off the toungue. Most of the time, it is the cane toad that is found to have this disease and most people here don't care about the cane toad so sick toads are too often ingored and left to rot.

Mucor is a genus of soil-based fungi, some species of which have global distribution. Mucor species have the important role of breaking down vegetative matter in the soil so that those nutrients can be freed up and absorbed by other living things. There are between 46 and 50 species of Mucor worldwide and some of them are responsible for respiratory and ulcerative diseases in animals including humans. Some species of Mucor are regularly found in house dust and these can cause irritation to asthma and allergy sufferers. Normally, Mucor doesn't attack an animal unless that individual is immuno-compromised. For example, Mucor infections can often be found in AIDS patients or those who have had recent surgery.

Mucor amphibiorum has been documented as causing fatalities in Australian frogs, toads and platypus. There may well be other species that are susceptible to Mucor problems but very little study has been done in this area. In the first three years that we received sick and injured frogs from the public, we only had one documented case of Mucor in a White-lipped tree frog (the first case known for this species). Since July 2002, we know that several of the frogs and toads we have sent for testing have returned positive for Mucor and it is likely that the increase in cases is because of the drought's effect on the soil microbial balance. Mucor is very tough and can survive such harsh conditions a lot better than many other microbials.

The soil ecology of the species Mucor amphibiorum has not been tested in laboratory conditions so the general ecology of the Mucor genus may or may not apply but this is some of the information that was given us by a soil microbiologist at the Soils CRC in Adelaide:

• Mucor is drought tolerant, doesn't like competition and has extremely hardy spores. As this drought has knocked out more moisture-dependent species of fungi from the soil, this has left drought-tolerant species like Mucor with 'the whole place to itself' so to speak. It can overtake the soil and might put out more spores than the frogs can cope with.
• The drought is also increasing the environmental stress on the frogs, making them more susceptible to diseases so they are more prone to attack by Mucor and other pathogens.
• Mucor prefers sandy soils and benefits by the practices of once a week watering (as opposed to daily), processed fertilizers (as opposed to pure manures), open areas (as opposed to being covered by lots of trees and shrubs) and lack of mulch over the soil. It does not like clay soil or other gardening practices which increase competitive fungi in the soil.
• Many species of Mucor are airbourne and can also survive in water if it contains decomposing plant material and droppings. In other words, a frog pond with plants and fish can easily be contaminated and sustain Mucor spores if a sick frog has been in it.

Mucormycosis doesn't always have reliable external symptoms (ulceration on frogs and crumbling ulcers are toads are possible) but it can be easily seen as grey-ish blue round nodules in the liver (see photo at top) when a post mortem is performed. The dying animal will often be very thin and doesn't respond to a normal sequence of treatment such as antibiotics or antifungals.

Mucor amphibiorum is a serious problem in platypus in eastern Tasmania and ulcerative dermatitis is commonly seen on those animals. Researchers there believe it arrived in Tasmania with frogs hidden in hands of bananas from north Queensland. Any dead platypus found should be tested for Mucor amphibiorum and reported to wildlife disease researchers such as the Australian Wildlife Health Network.

last updated: May 14th, 2005