The suspect, 40, was living with the girl's mom in an Everett apartment at the time.
Both the mother and daughter were diagnosed with a form of herpes almost exclusively contracted by sexual contact.
Prosecutors earlier this week filed a charge of child molestation against the man. The Herald is not naming him to protect the privacy of the victim.
"There is no cure for this disease and it is expected to afflict (the girl) for the rest of her life," deputy prosecutor Andrew Alsdorf wrote in court papers.
The Snohomish County Violent Offender Task Force has placed the suspect on its county-wide warrant list. Its top priority is identifying sex offenders accused of committing crimes against children.
"The task force has added the suspect to their ever-growing list of targets," Snohomish County Sheriff's Office spokeswoman Shari Ireton said.
The mother first became concerned about the girl's health in May 2012 because she was walking funny, court papers said. A pediatrician discovered a rash and reported the case to state Child Protective Services workers, who in turn notified the sheriff's office.
The girl initially was reticent about discussing what happened. Eventually, she opened up to her mother. She told her she was molested by the live-in boyfriend on more than one occasion.
She later told a child interview specialist at Dawson Place in Everett that she was scared she would get in trouble if she told someone.
She said the man "told her not to tell her mom because it would hurt her and also that he would hit her mother and sisters if she told," according to court papers.
A detective tried to track down the defendant to get his statement but the man moved out of the apartment when the doctor began to suspect abuse. The detective went to the suspect's employer at an auto detail shop but was told the man had quit and hadn't been heard from since.
Eric Stevick: 425-339-3446, firstname.lastname@example.org
More Local News Headlines
No answers more than 9 years after mother and daughter were murdered Neighbors band together to fight construction of 112 homes 14 nonprofits have launched an online initiative to seek donations Teen who sprayed mace at clerk said crime ‘looked easy’ on TV Public meeting: State parks leaders review past, ponder future Christian rocker shares lessons of grace from his own life Community Transit to expand Snohomish County routes in March Arlington man’s death in Camano Island fire deemed suicide
Our new comment system is not supported in IE 7. Please upgrade your browser here.