A San Francisco woman is not exactly the kind of person that most people want to have in their neighborhood. The presence of the woman, who was dubbed the "rat girl" because of her bizarre fondness for rats, raises concern because rat infestation appears to follow her wherever she goes.

The 43-year-old woman, who was identified only as Erica J. and is believed to be suffering from mental illness, is known to breed rats. In April 2011, the Animal Care and Control discovered that she was breeding hundreds of rodents in her room at a residential hotel on Minna Street.

Denise Bongiovanni, from the Animal Care and Control who saw the room, said that the rodents were burrowing through the walls of the apartment into other people's rooms. A video footage of the room also shows hundreds of rats going in and out of the trash, mattress and piles of filthy clothes.

"The rats have actually burrowed into other people's rooms," Bongiovanni said. "I was immediately concerned for the well-being of Erica. I believe that there's a serious underlying mental health issue that needs to be addressed and it seems to be unresolved."

The following month, public health officials exterminated about a thousand rats in Erica's room and in the surrounding areas.

Erica, who has been living in and out of the streets for the past three years, continued to breed rats though. Local residents, social workers and landlords report that she was breeding rodents. She was spotted with rats while living in a cart under a Japantown pedestrian bridge and most lately while living in a park.

On May 8, a video of the rat-obsessed woman was taken in a park at Golden Gate Avenue and Steiner Street with at least eight rats that were feeding from a bowl of dog food. The rats appeared to have taken over the park area as Bongiovanni said that the rats were breeding and burrowing tunnels.

Erica has since moved from the park. Officials from the Animal Care and Control have difficulty tracking her down but believe that the rat-obsessed woman already lives in a new housing. Still, Bongiovanni, said that it is likely that Erica will continue breeding rats until she gets the mental health treatment that she needs.

Rats pose health risks because they are disease carriers that can transmit potentially fatal diseases including hemorrhagic fever with renal syndrome, lassa fever and leptospirosis.