Sparky is a maniac around the Weed household. He'll "streak" through the halls at Mach 8 hoping to be chased, only to plop down on the floor if someone's in pursuit.

"He's very entertaining," said Helen Weed, who's been fostering the cat for about seven weeks. "He loves to have his tummy rubbed."

The energetic orange tabby is easily bored, but finds the most common of things fascinating: Blinds, strings and paper sacks. From all appearances, Sparky is the epitome of a healthy feline. But like many of his furry brethren, Sparky has feline leukemia.

Bobby Heller, executive director of Felines & Friends, calls Sparky's journey a classic second-chance story. He was transferred to the Santa Fe Animal Shelter & Humane Society from another shelter and tested positive for the virus.

"Most shelters euthanize positive cats," Heller said. "So we were called."

Weed, who volunteers with the nonprofit as a foster family, considers Sparky more of a fourth-chance cat. Dropped off at one shelter, transferred to the next, escaping euthanasia and given a chance through Felines & Friends, Weed hopes the cat will find a permanent home with a family who loves cats.

"He's such a healthy, happy cat, he doesn't deserve euthanasia," Weed said. "He's such a good guy."

The Weeds themselves can only foster cats on a temporary basis because of frequent traveling. But they have enjoyed taking care of the felines that come through their doors.

"We can't do it full time, but we can still enjoy them," Weed said. "It's nice that way, although we do get attached."

A previous foster cat, Chester, an older long-haired feline, is still looking for a home. Weed and her husband, Rick, often check the group's Web site to see if he's found the perfect match. "Chester is a beautiful cat," Helen Weed said. "He'd follow you around like a dog. But he doesn't like other cats. He'd be perfect for someone older, who was looking for a companion."

The Weeds often fostered cats at their previous home on the East Coast, Helen Weed said, after the family's longtime household cat died. Most of those foster cats were younger, usually abandoned or feral, and the Weeds would foster them until they were old enough to be adopted from a shelter.

The acrobatic Sparky would make a great home for someone with children, Helen Weed said. He loves the attention and simply likes to play.

Sparky is the only cat currently with Felines and Friends that has tested positive for feline leukemia, Heller said. The group does have several other cats awaiting homes that have tested positive for the feline immunodeficiency virus, considered less transferable because it's spread through blood. Both viruses affect a cat's immune system.

Because of Sparky's illness, he shouldn't be around other cats. While not contagious to other animal species or people, the virus can spread to other felines through saliva, nasal secretions, tears, urine and feces. Tests have shown that the virus can be passed to kittens through the milk of infected mothers.

The virus is commonly spread through fighting outdoor male cats. In some regions, it's estimated that one in 10 cats carry the virus.

The virus is not particularly hardy, according to veterinarians, which means it can't be brought home by exposure from other people touching a carrier cat or through an open window or airborne dust particles.

There's no cure for the virus, which can lie dormant in the cat's body for many years. A common vaccination helps cut the risk of infection to other cats. Veterinarians say the vaccines, which are administered in two doses about three weeks apart and maintained by annual boosters, are about 95 percent effective.

Sparky could live a full and healthy life, Weed said, but the fact that he could contract the second stage of the virus means he'll need someone who's passionate about cats.

During the early stage of virus infection, some cats' immune systems are able to shake off the virus, according to Cornell University's College of Veterinary Medicine. Heller said the group has had several cats initially test positive and then later have negative tests.

It's not possible to accurately predict the life expectancy of a cat with feline leukemia, according to veterinarians, but it's no longer considered a death sentence. The virus, however, can eventually expose them to secondary illnesses such as fevers, weight loss, infections and cancer.

Weed said Sparky doesn't require any special care at the moment. "I don't know what's going to happen if someone doesn't adopt him," she said. "I wish we could just keep him, but we can't."