Plague Rats – Prestige class of the city of Shenth

I have wanted to have a prestige class like this one for awhile. It's specifically only for one area of my game world, the city that once contained a plague that can never be fully eradicated. It exists just beneath the surface, with these rats doing what they can to treat the victims and ensure fewer people are infected.

Plague Rats – Prestige class of the city of Shenth. Named for the rats that carry the deadly plague that once nearly destroyed the city, but have been a constant threat for more than three hundred years. More than half of the members are dwarfs, as they were the ones who originally contracted the disease. They are honoured, despised and pitied by the other citizenry at the same time; these exterminators are needed, but due to the ever-present rotting smell emanating from them, they are more like a secret cabal of the near damned, tolerated as long as they are far away.

Unlike other prestige classes there is only way to join this group; contract the disease. Most people who contact this disease never become plague rats, but the plague carriers when they originally contracted the disease do not resist the contagion, thus their bodies adapts to become stronger with the disease than it ever did before. Most carriers never advance in the prestige class, but they can to enable them use the effects of their disease to their advantage.

Appear as a common person of their race, except they have small red boils on their hands that flare up and drip blood when they are scared or sick. When first infected these boils appear through-out their body but then settle down over a few weeks time as their body adjusts.

Hit Dice: D6 (unless their previous class is higher)
Requirements: To qualify to become a plague rat is to either roll a one on a saving throw or to deliberately forego a saving throw
Class Skills: as original class
Weapon and Armor Proficiency: as original class
Saving Throw: Advance as original class
Spells: If they previously had spells, they advance

1st level: Plague Carrier; Detect Disease; +1 charisma to infected
2nd level: Recognize stage of Disease; speak with animals; +1 level in all abilities of original class 3rd  level: Absorb Disease; +3 charisma to infected; +1 level in all abilities of original class 
4th level: Transmit Disease ; +1 level in all abilities of original class   
5th level: Adapt Disease; +5 charisma to infected; +1 level in all abilities of original class 

Plague Carrier: The individual is infected with the Shenth plague, and outside of divine intervention, they will always carry the plague within themselves. A carrier never suffers ill effects from the plague. They are passive carriers, as anytime a previously unexposed humanoid touches the individual; they must make a Fort save vs DC 2 to avoid catching the plague. If they pass this saving throw, they are immune to the disease, if they fail, see the Shenth plague entry.
Those who pass take an immediate -2 on their constitution and charisma for the next six hours. Those who fail their saving throw slowly starts to blossom with the red boils, and must make a DC 16 every day or suffer -1 cumulative charisma and constitution until either reaches 5, then they reverse and slowly increase to its natural point.

Detect Disease: per the spell in the player’s handbook; as an innate spell.

Charisma bonus: The infected will automatically recognize a carrier, and will respond positively to him or her, gaining extra bonuses as they increase in level.

Recognize Disease: Plague rats may make a spot check (DC 12) to determine if someone has been affected by the disease, how long they have had it and at what stage of infection they are in.

Speak with Animal: used primarily to speak with the rats that inhabit the lower levels of the city

Absorb Disease: Upon laying their hands on an individual affected by the plague, they are able to cure the inflicted and remove the plague from anyone except another plague rat. Any charisma loss however is permanent. If someone doesn't want to be cured, they cannot be cured through this method.

Transmit Disease: While plague rats are always passive carriers, at this stage, a plague rat can infect others with the plague with full effects without touching them. Those whom the plague rat wishes to infect can be within forty feet and the plague rat can see them. Upon two rounds of concentration, the victim must make a Fort DC 15 or be affected with the disease.

Adapt Disease: Perhaps the most insidious of all their powers, at this stage, the plague rat can adapt the disease so that it will affect one type of creature. So, they can change the plague to effect elves or giants only. It takes ten minutes of uninterrupted activity to adjust their body chemistry. They use this so they can more easily blend in.