NAIROBI, Kenya (AP) — The deaths of 15 elephants over the past month in Kenya ‘s Amboseli National Park have sparked an investigation, wildlife authorities said Tuesday.

The Kenya Wildlife Service said 10 of the pachyderms showed signs of partial paralysis before dying within two days, while the remaining five were found dead, with their carcasses partially consumed by scavengers.

Most of those affected were female elephants and their calves, with only one male among the dead. The deaths happened in the Kimana Sanctuary and Kuku Ranch areas surrounding the park, the authority said.

Kenya has previously recorded incidents of elephants being poisoned as a result of poaching and human-wildlife conflict.

Preliminary tests on samples collected from the elephants by a laboratory at the University of Nairobi detected a “potential toxic substance,” while separate analyses by the Government Chemist were negative for the toxins tested. The authority said further tests are underway.

“Environmental investigations are also being undertaken, including the analysis of water sources and other potential environmental contaminants within the affected areas, to establish whether the elephants were exposed to a common source,” the authority said in a statement.

The authorities sought to reassure the public, saying there was no evidence the condition could be transmitted to humans.