Note: This is only background info that would directly affect the main characters. Every area has their own history with infected people, I'm just focusing on Europe, Asia, and America. O:
"Infected" is the current politically correct term for persons with a certain genetic mutation that can manifest after traumatic experiences or, in more recent times, at random. It often carries physical mutations as well as super human abilities that can range from harmless to deadly.
In mideavl Europe most infections were thought to be the work of the devil. "Demons," a slang term still used today in some parts of the world, were often children and young adults who spontaniously took on the appearence of Biblical demons (the appearence of which were probably based on infected people in the first place.) Wings, tails, horns, fangs, and manic personality changes were very common and often led to the death of the host, usually by burning at the stake or hanging--whatever was most fashionable at the time.
In the 1600s, fearing for their safety, boatloads of European families with infected children stole away to The New World. A few were caught (some historians have linked it to the begining of the Salem Witch Trials, but many disagree) but most moved onto the Rhode Island colony, which was well known for tollerance. It is believed that this is the reason that so many modern infections found in the Boston area are "demonic" in appearence. (Devlin's red eyes, for example, are most likely a throw-back to the old skool manic infection)
After generations of infected persons being killed, the mutation stared to evolve, making it harder to notice. Changes in hair color, similar to what happened to Crow, became the norm by the 18th century. Extreme hair color change, like Tabbi's, is fairly new. In modern times, having the full on, old-skool manic infection, like Tadhg, is extremely rare. Fortunately, through medication and proper treatment, doctors are finding that the crippling manic personality trait can be destroyed by the time the host reaches their early twenties, alowing them to live a normal life. Until then, however, it can be a bumpy ride.
After the terror attacks, the number of infections in the Greater New York area trippled, making the area a haven for infected persons trying to live a normal life.
Where infected Europeans were treated as hellspawn, infected Asians, especially in Japan, were treated like Gods. Though not always the case, most infected people were born with animal characteristics, similar to those in asian mythology. Unlike the Europeans, the asian infected gene has remained the same for generations, giving the host a half animal half animal appearence that would be passed down through families for generations. Most "Furries" have no non-furry reletives, though not all furries have useful abilities. Some may never notice them while others can have abilities that are very useful if not dangerious. It varries person to person.
Despite claims, it is proven that furries are as human as any other race and could have a healthy child with any other race.