Frog chytrid fungus

Scientists think the decline and disappearance of some frogs species in Australia and overseas may be partly due to a disease caused by a chytrid fungus.

Two frogs with Chytrid infection

The fungus attacks the parts of a frog's skin that have keratin in them. Since frogs use their skin in respiration, this makes it difficult for the frog to breathe. The fungus also damages the nervous system, affecting the frog's behaviour.

A sick frog may:

  • have discoloured skin
  • be sloughing, or peeling, on the outside layers of its skin – this can vary from obvious peeling of skin (particularly on the feet) to a roughness of the frog's skin that you can barely see
  • sit out in the open, not protecting itself by hiding
  • be sluggish and have no appetite
  • have its legs spread slightly away from itself, rather than keeping them tucked close to its body. In more extreme cases, the frog's body will be rigid and its back legs will trail behind it.

Chytrid fungus is probably transferred by direct contact between frogs and tadpoles or through exposure to infected water. The disease may not kill frogs immediately, and they can swim or hop to other areas before they die, spreading fungal spores to new ponds and streams. This means it is very important not to move frogs from one area to another.

Wet or muddy boots and tyres, fishing, camping, gardening or frog-survey equipment may also be contributing to the spread of the disease.

Help stop the spread of chytrid fungus

Please take the following precautions if you intend visiting frog habitats in the wild, including nature ponds in parks or gardens:

  • Only touch frogs when absolutely necessary. Remember to use disposable gloves, sample bags and sterile equipment.
  • Clean and dry all equipment and wet or muddy footwear before and between visiting frog sites. This may include cleaning the tyres of your vehicle before visiting known high-risk sites where threatened frog species may live.
  • Never move a frog from one area to another.
  • Carry cleaning utensils and a disinfectant for use between sites.

What to do if you find a sick frog

Some of the symptoms of chytrid fungal infections are described above. If you think you've found a sick frog, or if you see a frog which has died recently from no obvious cause (ie. not killed by a car), please:

  1. Place the frog into a container without directly touching it.
  2. If the frog is still alive, make sure the container is escape-proof and has a few small air holes and a small amount of water. Ring the Frogwatch Helpline on 0419 249 728 for an opinion on whether the frog is sick or whether it is likely to survive transportation. If the frog is dead, put the container into a plastic bag and into your freezer as soon as possible.
  3. Consult the Hygiene guidelines for instructions on how to send frozen or live frogs by courier to a laboratory and how to be reimbursed for your expenses.

 

What is keratin?

Keratin is a type of protein. It's in your hair, and in your skin. Other animals have it in their feathers, fur and scales.

Keratin forms a tough, impervious, waterproof layer that protects animals, stopping unwanted substances in the outside world from getting into their bodies. It also builds up in areas of the body that get exposed to lots of wear and tear. Have you ever had a callous on your hands or feet? That's keratin.

As keratin builds up in cells, the cells die and eventually peel away. People shed cells gradually, losing small amounts of skin and hair all the time. Snakes and other reptiles do it more quickly, shedding their skins - and their keratin - in one go.

Keratin in frogs

A frog needs its skin to be thin, moist and pervious to things from the outside because it breathes through its skin. Frogs have simple lungs, which do not give them all the oxygen they need. They have to absorb oxygen from the air or water through their skin. If their skin was full of keratin, they would not be able to do this.

Frogs only have keratin in the parts of their body that get exposed to wear and tear - such as their hands and feet, and the places where their legs rub against their bodies. Tadpoles only have keratin around their mouths, to help them scrape food from the bottom of their pond or stream. As they develop into frogs, they grow keratin in other parts of their bodies.

How the frog chytrid fungus spreads

The chytrid fungus only attacks the parts of a frog's skin that have keratin in them. Tadpoles can be infected around their mouths, but this is not enough to kill them. It's only when they start turning into frogs, and grow keratin in other areas, that the Chytrid fungus can spread throughout their bodies.

They may then die from the disease - but not before they've hopped and swum around, spreading the fungal spores to other ponds and streams. Once a pond has become infected with chytrid fungus, the fungus may stay in the water forever. This means it is very important not to move frogs from one area to another.

Tadpole with keratin areas around mouthStage 1: tadpoles only have keratin (shown in red) in their mouth area, so they can scrape algae and decaying vegetation from the bottom of a pond or stream. Chytrid fungus only affects their mouthparts.

Tadpole with legs and keratin on feetStages 2 and 3: as the tadpole develops legs, it grows keratin on its feet and hands, to make them tougher. Chytrid fungus in the water can infect these new areas of keratin.

Froglet with keratin areas on legs and tailStage 4: the tadpole develops into a froglet, and keratin grows on other parts of its body that need to be protected from wear and tear. Chytrid fungus can now spread to many parts of the frog's body.

Resources

Protection of native animals

All native birds, reptiles, amphibians and mammals, but not including dingoes, are protected in NSW by the Biodiversity Conservation Act 2016.