Chytridiomycosis

Question 1

Cause

Answer 1

• Caused by the chytrid fungi Batrachochytrium dendrobatidis.
• Bd is a waterborne fungus that disperses into the environment to search for a new host.

Question 2

Distribution

Answer 2

• Chytrid fungus which has a preferred temperature range between 17 and 25 degrees Celsius. The fungus dies at temperatures at and above 30 degrees.
• Chytrid disease is known to affect over 350 species of amphibians, though it appears to be impacting frog species most severely. However, the disease does not affect all frog species.
• Chytridiomycosis is present on every continent except for Antarctica, though the disease is having the biggest impact in South and Central America, Australia, and North America.

Question 3

Transmission

Answer 3

• Contact with contaminated water/water containing zoospores.
• Direct contact between frogs
• Chytridiomycosis is easily spread by human activity. Boots, clothes, and equipment should be cleaned. Wild amphibians should not be moved between habitats.

Question 4

Life Cycle

Answer 4

• Fungus produces zoospores.
• Spores are produced by asexual reproduction.
• Zoospores are released into water or reinfect the host.
• Zoospores swim and encounter a host.
• Spores invade the surface layer of the skin.
• Spores develop into a thallus and the thallus matures.

Question 5

Impact on host

Answer 5

• Affects the nervous system.
• Affects frog’s behavior - sit out in the sun.
• Sluggish, no appetite.
• Has its legs spread away from itself.
• Affects part of frog’s skin that has keratin.
• Causes skin cells to shed/thicken/harden.
• Disrupts the function of skin cells.
• Frogs use the skin to exchange gases and water and salts.
• Leads to osmotic problems.
• Frogs die.
• It is not yet known exactly how the fungus kills amphibians, but it is thought that it may cause mortality by disrupting the normal function of the skin resulting in electrolyte depletion and osmotic imbalance.
• Many frogs experience a thickening of the skin, which may prevent oxygen exchange, and impair thermoregulation, nutrient intake, and hydration. Secondary skin infections with bacteria can occur.

Question 6

Treatment

Answer 6

• In captive amphibians, chytridiomycosis can be successfully treated with antifungal medications and by disinfection of contaminated enclosures
• Most common method uses are series of baths in the drug itraconazole
• Treatment is not always 100% successful and not all amphibians tolerate treatment well
• There are no good methods for the treatment of wild animals in the natural environment as it is impossible to get enough of the antifungal medications into the environment to be able to successfully rid infected frogs of Bd

Question 7

Prevention/control

Answer 7

• Captive amphibians should not be released into the environment or used as fishing bait
• All newly acquired captive amphibians should be initially quarantined from other amphibians units it has been confirmed that they are disease free
• It is a reportable disease and any detection of the disease should be reported to the appropriate wildlife authorities
• Only touch frogs when necessary and use disposable gloves, sample bags, and sterile equipment.