Millicron

Millicrons are a species of sapient airborne microorganisms which can infect human bodies causing a severe fever. Despite being a pathogen for Humans, the Millicrons are actually civilized creatures, the disease they cause being unintentional. Therefore when one is infected with them it is necessary to seek out a treatment that wouldn't involve genocide (such as using antibiotics). Instead, the Millicrons must be carefully evacuated from the host.