The Plagued

The infected come from another realm, it is unclear what the realm is or its exact nature but a number off aspects have been noted.
There are two subtypes of the infected, the aetherplagued and the psiplagued. Both types of infection are primarily caused by psionically active spores which in inhaled or injected via an attack by an infected will lead to guaranteed infection of the individual, even of those creatures normally immune to disease, the only creatures who seem resistant to the infection are those who are immune to psychic attacks. If affected by large sources of heat such as flame instead of becoming damaged the infected will rapidly evolve to counteract it progressing to the next stage early and often rapidly expanding as it alters the host to suit its needs with the extra energy, however the heat will temporarily halt any regenerative effects of the host. There are three stages in a traditional infected life cycle.

Stages of Infection

Infiltrator

The infiltrators are the first stage of infected and will show no external signs of infection, but will be under the control of the spores, trying to find other hosts to incapacitate to spread the infection to. The spores are able to use the memories and personality of the host body to enable better infiltration and infection.

Exposed

The exposed are the second stage of infection. At this point black oozing fungal growths will begin to appear, often altering the physical form and skeletal structure to better assist i its role. Whereas the last stage was meant to subtly infect this form is much more blunt and aggressive. This stage operates with enhanced hearing and will go towards loud sources of noise. A common form of attack is to spontaneously erupt a skeletal spike at the end of a tentacular appendage to pierce the skin and spread the infection to the target.
When close to evolving to the final stage to will find an open space to stand at.

Tree

The tree stage is the final stage of infection. The infection alters the bones and organic tissue to turn the creature into a tree like structure that emit constant levels of spores. This can alter the local environment overtime to one more suited for the infected. Cutting open a tree will lead to all nearby infected being psionically altered and they will converge on the location to defend the trees.

The Aetherplagued

The aetherplague seems like the strongest form of infection. This i believed to give hints to the plagues origins as being from another plane not yet recorded by researchers from the Five Kingdoms. The aether plague has the chance of instead forming dominant hosts who instead of fungal growths will instead have their bodies converted to producing plague oozes.
The oozes will try to enter new creatures via any openings available and then begin converting the new host into another dominant host. When not engaged in strenuous activity dominant hosts will begin to emit spores which will produce normal psiplagued victims. The tree stage still will occur but much later with dominant hosts. Tree stages of dominant hosts will secrete a sap like substance that with enough time will form into new aetherplague oozes, each of the dominant trees connecting with others even on other planes as part of the gestalt consciousness of the infection swarm.

The Psiplagued

The psiplague is the normal form of the infection. It is spread either by inhaling spores or by being physically attacked by an infected and the spores entering through a cut or other means. Most psiplagued not under the control of a dominant aetherplague infected creature, will run on the instincts of the spores to generally aim to spread the infection at all costs.