Helminth Charger is an infested type of Kubrow that is obtained after interacting with Helminth, who is behind the infested door in your liset and is only accessible with the new Warframe, Nidus.
After interacting with Helminth, you’ll have a choice to be infected by Helminth where he stabs your Nidus in the neck and you’ll be infected. You can infect and be infected by others players outside of the relays. You will know you have been infected if there is a pink cyst on the side of your Warframe or hear a distinct sound when in Nidus. After 7 days of being infected, the cyst can be used to breed the Helminth Charger.