earticle

영어

Batrachochytrium dendrobatidis, also known as Bd, is a pathogenic chytrid fungus that affects amphibians all over the world. The fungus is known to have lethal effects to its host and is suspected to lead to endangerment of several amphibian species around the world. However, not all infected individuals show clinical symptoms and Asian amphibian species have been recorded to show immunity towards the fungus. We have conducted infection and recovery experiment in wild caught individuals of Japanese tree frogs (Hyla japonica) to analyze the infection rate of animals exposed to differential dosage of Bd and the recovery rate with extended heat exposure. We collected adult individuals of Hyla japonica from 4 different ponds located in South Korea, namely Nakseongdae (37.47° N, 126.95° E), Incheon (37.46° N, 126.76° E), Gwangju (37.47° N, 127.30° E), and Pocheon (37.89° N, 127.29° E) during the breeding season between May and August 2016. The experimental subjects were tested three times for Bd through PCR assay using the swab samples collected during different steps of the experiment. The initial screening was done using the samples taken as soon as the animals were collected from the wild. The second screening was performed with the swab samples taken after the infection and recovery process, and the third screening was performed after 3 weeks from the second screening only on the recovery group to confirm the results. Infection process was conducted with 45 naturally uninfected animals at three different level of zoospores/ml – 100,000 zoospores/ml, 200,000 zoospores/ml, 300,000 zoospores/ml and control group for up to six days. The 1ml of the diluted culture was inoculated directed to the infection group animals. An additional 19ml of distilled water would be added to the container and the frogs were maintained to have direct contact with the water at least 2 hours a day through turning of the container. During the third day of infection, another 1ml of diluted culture was inoculated to the infection group animals in the same manner. The infection rate of each group was 100,000 zoospores/ml (42.11%), 200,000 zoospores/ml (50.0%), 300,000 zoospores/ml (66.67%) and control group (0.0%). Overall, the infection rate of all the group was 45.44%. Mortalities during infection procedure in infection group was 42.86% (15 out of 35 animals died), while none out of 5 animals died in control group. Recovery process was conducted at the temperature of 32℃ for 4 days with 6 naturally infected animals and 31℃ for 7 days with 21 naturally infected animals. The recovery rate of first 6 animals was 0%, which means all of 6 animals testing positive for Bd screening in the post recovery procedure. However, all the animals were recovered in second group, although two animals died during the process. The results may support conservation efforts and help to study the effect of climate change and temperature difference to the current Bd epidemic.