CLEMSON, S.C. (AP) — Three horses in South Carolina have tested positive for equine infectious anemia, a blood-borne, potentially deadly illness.

According to the Clemson University Public Service and Agriculture unit, the first case was in a quarter horse in Berkeley County.

The other two quarter horse cases are in Barnwell County. State Veterinarian Michael Neault said in a news release Friday that these are the first cases of the illness in South Carolina since 2014, when a donkey tested positive in Aiken County.

The virus that causes EIA is often transmitted by bloodsucking insects like biting flies but also can be introduced by infected needles or other medical, dental or tattoo equipment.

Neault says the illness does not affect humans but is potentially deadly to horses and other equine species.