Even as officials blame infected mongoose for the deaths, the samples of a dead rat, found inside the deer enclosure, have also been sent for tests.

Mail Today reported about a spate of deer deaths following which an inspection by a three-member team of the Central Zoo Authority (CZA) and representatives of the Indian Veterinary Research Institute (IVRI) revealed that the toll was 33.

However, the Delhi zoo spokesperson maintains that the number of deaths remains 16 and some infant or newborn deer died during the period. "Only 16 deer have died of which 13 tested positive for rabies.

There were some infants and still born deer which are not included in this list," said Riyaz Khan, curator of the Delhi zoo.

Mail Today, however, got access to documents and postmortem reports of the hospital and the animal house inside the zoo, which revealed 33 adults and six infant deer died since February.

The cause of death is different and officials are yet to ascertain reason behind spread of rabies virus.

"After the inspection of the zoo, we have instructed the officials to clean entire area and sanitise it. They have been asked to quarantine the deer enclosure by white washing and disinfecting the area. As the reason behind spread of rabies virus is not certain, a daynight vision CCTV cameras will be installed to monitor any external entry," CZA member secretary DN Singh said.

CZA has also instructed the zoo to monitor movement of deer with binoculars to notice symptoms of dullness or injury.

A body of a rat was found inside the deer enclosure, which has been sent to the lab to check if it was infected by rabies. Officers are guessing that spread of rabies is due to bite of infected mongoose or rat.

The zoo officials were also seen defending their act of transporting two male Himalayan black deer from Gopalpur in Himachal Pradesh last week. This is in violation of CZA guidelines, which says no animal should be transported during summers.

"Both the male deer were transported through an exchange program and we took extreme care of the animals.

As deer is a high altitude animal, it was kept in a special van maintaining room temperature and it was transported to Delhi only at night so that temperature remains low. They were brought only after the approval of CZA," Khan explained.

However, the CZA approval was granted six months back. Officials claim that the delay in transportation was due to unavailability of logistics and infrastructure.

Khan further said the animals will be kept under observation in a temperature-controlled room inside the hospital. Male black deer have been brought to breed with four female deer present in the zoo. "These animals mate during the winters so it was important to bring them here now so that they get some time to acclimatise.

They will be let out in the open only after rains in August," Khan said.