Chabakaew, a baby elephant saved after falling into a septic tank last year and taken care of by park officials, died on Wednesday at the Phu Wua Wildlife Sanctuary in Bueng Kan province.
Wanchai Chariyasetthachoke, director of Protected Areas Regional Office 10 (Udon Thani), said veterinarians of the Department of National Parks, Wildlife and Plant Conservation are performing an autopsy on the elephant.
They suspect the calf may have died from Elephant Endotheliotropic Herpesvirus (EEHV), or bad bacteria in its digestive system.
Mr Wanchai said the disease may have been caused by two factors, rapid fluctuations in the weather since the onset of the cool season this month and the elephant's weak immune system.
The change in temperature during the day may have led to the elephant to develop stress.
Since early this month, temperatures in the sanctuary have fallen dramatically to 12-14C in the morning before rising to more than 30C in the afternoon. The elephant may have had trouble coping.
The calf got lost from his mother and fell into a septic tank in a village near the forest in April last year.
After it was rescued it was placed in an elephant conservation centre where it received immediate treatment before being brought to the sanctuary to recover and be looked after.