Bacteria and toxoplasma infection - which involves parasites in blood and body tissue - caused the death of a female giant panda at Zhengzhou Zoo, according to the findings of a monthlong investigation, zoo authorities confirmed on Wednesday.

But experts are still wondering how the panda became infected at the zoo, which is located in the capital of Henan province.

On Feb 9, Jinyi, the female panda, died at the age of 7. Since pandas are normally expected to live up to 25 years, the death aroused particular attention.