Pressures on the World Heritage Area - Diseases

Diseases are caused by pathogens such as a fungi, viruses, bacteria orparasites. Pathogens can be carried by water, air or soil. They can be carried by insects, animals and plants. They are generally difficult to find, so we don't know much about them. Diseases which affect agricultural and horticultural crops can spread to rainforest species, especially related fruit trees such as native banana trees. This page deals primarily with two major pathogens which are attacking vegetation and frogs.

Phytophthora

Phytophthora cinnamomi is a soil-borne organism, often known as a root-rot fungus. It can cause dieback amongst some or all species of vegetation in the rainforest and sclerophyll forests. First discovered in the 1970s near Koombooloomba, over 200 patches have since been found - mostly in wet notophyll vine forests above 700m on acid volcanic soils (14% of the World Heritage Area). The long term recovery of affected areas remains unknown. The EPBC Act lists forest dieback caused by the pathogen Phytophthora cinnamomi as a ‘key threatening process’ throughout Australia .

Phytophthora can be present without killing vegetation. No one is sure what triggers it to cause dieback. The disease is spread by the movement of soil and water. It is suspected that soil disturbance or movement associated with the construction of a road or walking track may be a cause of virulent outbreaks. However, vehicles, bushwalkers and pigs may still transport infected soil from one place to another and cause new outbreaks. Mixing of different types of the pathogen may also be a trigger for virulence. There have been several other species of phytophthora detected in the Wet Tropics and little is known about their role. Deadly outbreaks of phytophthora may also be caused by other stresses on vegetation such as drought or previous logging activities.

Remember that dieback patches are not always due to phytophthora. They can also be caused by factors such as drought, lightning strikes and insect infestation. Dieback of rose gums has been found in various locations along the western edges of the Area including Julatten, Ravenshoe and Wallaman Falls areas, but it is unlikely that it is caused by phytophthora. The exact cause remains unknown.

A map of phytophthora distribution and highly susceptible areas in available here.

A guide to phythopthora and its prevention is available here.

Frog chytrid fungus

There is a variety of diseases which affect frogs in the Wet Tropics. Chytrid fungus (or Chytridiomycosis) occurs in upland and lowland stream dwelling frogs in the Wet Tropics. Several species of upland frogs are now presumed to be extinct. It has been listed as a key threatening process under the Environment Protection and Biodiversity Conservation Act and a Recovery Plan has been developed.

Frog chytrid fungus was discovered in 1999, but may be responsible for frog population declines in the region dating back to the 1970s. The spores of the fungus grow inside the outer layers of the frogs' skin, resulting in keratin damage that may kill frogs within 10-18 days. The exact mechanism by which chytrid fungus kills infected frogs is still unknown.

Spores of the chytrid fungus are transported via water and wet soil. Wet or muddy boots and tyres, and other equipment, may be contributing to the spread of the disease, as may feral and native animals.

For more information about chytrid fungus and its impacts on frogs, see the JCU frog diseases website.

For more information about various frog diseases in the Wet Tropics area, see the website for the Cairns Frog Hospital, the care centre for the Frog Decline Reversal Project.