An unknown disease is killing wild horses in Waipiʻo Valley on Hawaiʻi Island.

Locals say there are between 30 to 50 wild horses roaming in three herds in the valley.

And within the past two months, it’s believed 10 horses have contracted some sort of disease and died.

The horses will first present an abnormal gait as their muscles begin to atrophy – eventually leading to the animals not being able to walk at all.

State and local officials, with help from the community, have been investigating what is affecting the animals.

Initial blood tests from several horses have ruled out any contagious or newly introduced disease – but officials have not yet determined what is killing the animals.

Tim Richards is a Hawaiʻi County Councilmember and veterinarian.

Richards says further test samples from a deceased horse have been sent for analysis – and they are waiting for the results.