In January, a team of experts led by Luo Qingli, an ophthalmologist at Chengdu Huaxia Eye hospital, and Ran Yuping, a dermatologist at West China Hospital in Chengdu, were brought in to determine the source of the problem.
According to Luo, they examined two pandas, Yongyong and Xiaoya, and found the iconic black circles around their eyes had become white due to a loss of fur.
"Both pandas had shed fur around the eyes," Luo said. "Yongyong, the one with a more serious condition, also had ulcers around the eyes."
Twelve pandas had contracted the disease, Luo said. The cause was unknown.
Sichuan is much more humid than other areas of China, offering a favorable environment for the spread of bacteria and mites. Some of the pandas are sensitive to the bacteria, a base employee told news website ThePaper.cn.
Mites are about 0.5 mm in length and may transmit diseases in certain conditions.
The base issued a statement in January, saying that no more than 10 pandas had contracted the disease.
The base is actively cooperating with experts from Sichuan Agricultural University to tackle the disease, the statement said.
They had received treatment previously, but the medicine didn't work as expected. All of the infected pandas have been quarantined and will receive another round of treatment with new medicine, it said.
The base has since declined to release information about the condition of the panda. A base official said on Wednesday it has no plan to issue further statements about the pandas' health.