The zoo in the Pakistani capital, Islamabad, has been closed temporarily after tests confirmed an outbreak of the deadly H5N1 strain of bird flu.
A number of peacocks at the zoo tested positive for the virus
Twenty-four birds of different types have died at the zoo since 12 February and authorities have been vaccinating birds against avian flu.
Earlier this month the virus was found in chickens in nearby Rawalpindi.
Tests are also being carried out on staff who work at the zoo, particularly those in close contact with the birds.
Bird flu normally only infects birds and, though it can be contracted by humans, scientists say the chances of this happening are extremely low.
The H5N1 virus does not at present pose a large-scale threat to humans, as it cannot pass from one person to another.
However, experts fear the virus could mutate and in its new form trigger a flu pandemic, potentially putting millions of human lives at risk.
Last March H5N1 was found in north-west Pakistan, India and Afghanistan.