Extended response

Question 1

Amphibian chytrid fungus disease

Answer 1

Chytridiomycosis disease is caused by a fungus called Batrachochytrium Dendrobatids

Question 2

symptoms of chytridiomycosis

Answer 2

Skin gets thickened and hardens. Respiration becomes difficult because significant gas exchange usually occurs across moist skin under normal conditions. The amphibian can become lethargic. Hind legs extend, and the amphibian becomes sluggish and has no appetite. These symptoms can lead to death.

Question 3

What is the incubation period of chytridiomycosis

Answer 3

2 - 10 weeks. death follows the onset of symptoms within 2-3 days

Question 4

what are the six steps in the life cycle of chytridiomycosis

Answer 4

1. Zoospores are produced and released from a mature zoosporangium (thallus) discharge tube
2. Zoospores swim a short distance or are carried by water currents
3. zoospores encounter a new susceptible host and attach to and penetrate a skin cell. This is the portal of entry
4. The cells invade the skin, absorbing nutrients. A new zoosporangium develops via asexual reproduction
5. The zoosporangium matures and zoospores are produced
6. Chytridiomycosis damages the frog’s skin causing reduced respiration and osmoregulation, leading to death

Question 5

Zoospores

Answer 5

a spore with a flagellum

Question 6

Flagellum

Answer 6

a whip like tail which provides zoospores with locomotion

Question 7

how is chytridiomycosis transmitted

Answer 7

occasionally direct via skin to skin contact. Indirect waterborne and soil transmission is more common. Zoospores are released by infected frogs via a zoosporangium (thallus), then swim through the water to attach to and penetrate the skin of a susceptible amphibian

Question 8

unique future of chytrid fungus

Answer 8

They lack hyphae. Instead they grow a spherical, smooth walled zoosporangium or thallus. Inside asexual reproduction occurs, producing new zoospores. The thallus contains a plug that is removed once the thallus matures, releasing the zoospores into the water

Question 9

what are the three reasons that this fungus has spread so widely and so quickly

Answer 9

• Virulence of the pathogen (whether it has increased or evolved recently)
• The environment (whether there are more suitable environmental conditions for the growth and survival of the fungus in its reservoirs)
• The host (whether there is a reduced resistance to infection in frog populations)

Question 10

what is the portal of entry

Answer 10

Via skin penetration (invades other layer of epithelium)

Question 11

what is the site of replication

Answer 11

Via asexual reproduction inside the thallus (zoosporangium)

Question 12

what is the portal of exit

Answer 12

Via zoospores going from the thallus in the skin of an amphibian into the water

Question 13

what are the biological issues related to management

Answer 13

• Fungus is temperature sensitive, confined to the relatively cool, wet areas
• Frog resistance to infection may be reducing by environmental stress (climate change or increased exposure to UV radiation)
• Vaccines have been tested but no differences in mortality or virulence have been observed

Question 14

Strategies of prevention and control

Answer 14

1. Efforts aimed at protecting uninfected areas
2. detect new outbreaks, establish restricted and control areas (quarantine)
3. Identify and prioritise frog species at risk of extinction
4. Monitor impacts on frogs, especially populations who recover naturally
5. Implement hygiene protocols for bushwalking, disinfecting vehicles
6. Develop a central info storage site to upload and access data
7. there is no cure

Question 15

shade map of distribution

Answer 15

Eastern Australia (from north Queensland to Melbourne, Victoria)
• South West of Western Australia
• Adelaide
• Tasmania

Question 16

what are three reasons a species may become threatened due to this disease

Answer 16

• Occupy restricted geographic range
• small population size
• Habitat suited to growth of fungus (temperature, rainfall

Question 17

Explain an advantage and a disadvantage of not having a resting stage in the life cycle for this
fungus

Answer 17

Advantage: rapid growth/short life cycle. allows pathogen to establish quickly in new area
Disadvantage: adverse conditions, pathogen may not survive

Question 18

what are the diagnostic laboratory tests available to scientists

Answer 18

• Microscopy (direct examination of skin scrapings and immunoperoxidase)
• PCR

Question 19

State two disadvantages of direct examination of skin scrapings.

Answer 19

• Only small samples of skin can be used without sacrificing the animal
• Reduced chance of detection in healthy frogs with a light infection

Question 20

State two advantages of using immunoperoxidase

Answer 20

• stains antibodies, used to confirm infection
  Able to detect light infections of the disease
• Toe clippings can be used, does not require destruction of the amphibian

Question 21

State two advantages of using real-time PCR

Answer 21

• highly sensitive, able to detect light infections of the disease
• quantitative, indicates level of infection