Chytrid Fungus

The causative agents of chytridmycosis, Bd and Bsal are species of microscopic fungi that has resulted in the spread the disease and mass mortality across six continents and even the extinction of some species. Bd is a known to infect amphibians worldwide and Bsal is currently thought to be restricted to Europe and Asia where it infects newts and salamanders.

It is thought that chytrid fungus causes mortality by blocking sodium uptake channels on the skin surface; the lack of sodium results in poor circulating and the heart ceases to beat. Typical symptoms include skin reddening, excessive skin shedding , seizures or atypical behaviours (e.g., daytime activity in nocturnal species) and abnormal posture.

The infectious stage known as the zoospore is motile in water and latches onto host amphibians where it develops before shedding more zoospores into the environment.

Although it is shown that many amphibian species in the UK and Ireland have been infected, not all species are susceptible, with some showing some tolerance (e.g., Natterjack toad). Treatment is not possible in the wild.

• For eDNA sampling, it is vital biosecurity is taken into account in survey design to reduce the spread of chytrid fungus. Thoroughly disinfect all footwear/waders and equipment before entering the sampling site or moving between sites. ARG UK (2017) has produced an advice note for working with amphibians to reduce the spread of the chytridmycosis to new regions including stringent biosecurity measures. 
• To maximise the chance of detecting the presence of Bd infection, natterjack toads should be sampled at natterjack breeding ponds in the spring, whilst common toads should be skin-swabbed in the summer.
• Traditionally surveying amphibian populations for chytridiomycosis involves trapping individuals and swabbing the skin. At least thirty adult or juvenile individuals should be caught and swabbed on the same day to ensure confidence in disease detection. Surveys should be undertaken once in spring and again in summer. Swabs are then sent for qPCR analysis.
  This method of surveying requires a lot of equipment and prior training for staff and volunteers. Species protected under UK legislation such as natterjack toads and great crested newts will require a licensed surveyor to be present. *If you would like to survey for chytrid fungus following this method and are a license holder, please do get in touch via our contact us form*