Discovery Season 3 Episode 4 Will Change The Series Forever

The process of joining isn't easy. Potential hosts basically have to go to Trill boot camp to even be considered for joining. Once host and symbiont are joined, they cannot be easily separated. If they are, it's possible that both entities will perish. Given those serious limitations, can human beings (or any non-Trill species) act as host to Trill symbiont? We get what has been the standard canon for decades of Trek lore in the first appearance of the Trill.

In "The Host," we are introduced to Odan (Franc Luz) an ambassador seeking to mediate an ongoing conflict between the Alphans and Betans of the Pelians. When Odan is mortally injured, Dr. Beverly Crusher (Gates McFadden) becomes the first member of Starfleet to learn about the existence of the Trill symbiont. Before Odan dies, it is decided that Commander William T. Riker (Jonathan Frakes) will be temporarily joined with the Odan symbiont until a new, permanent host can arrive.

While Riker acts as host to Odan successfully at first, he experiences life-threatening side-effects almost immediately. While Crusher is able to give Riker immunosuppressants to reduce the effects, the truth is clear: The human immune system will fight the symbiont and force it to either leave or die.

Adira, on the other hand, suffers no physical maladies from the joining — at least none that we're aware of. Their only side-effect is that they temporarily lose some of their memories as a result of the specific emphasized by the joining. The only difference that we're aware of is that Adira and Gray are in love. With the Trill homeworld in peril on Star Trek: Discovery, this huge change to the lore is a potentially life-saving one for the Trill going forward.