A flesh-eating parasite infesting livestock in Texas is prompting new restrictions on the importation of shelter pets to Vermont.

A legislative panel approved an emergency rule Thursday that requires domestic dogs and cats to be inspected for New World screwworm within five days of arriving in Vermont. The rule, which also requires pets to be treated for the parasite, applies to animals coming from “infested zones,” all of which are currently in Texas.

Vermont State Veterinarian Kaitlynn Levine, who works in the Agency of Agriculture, said the spread of New World screwworm northward threatens all livestock operations in its path.

“We don’t import a lot of cattle from Texas. What we import a lot of are cats and dogs through the rescue trade,” Levine said this week. “And so we are very concerned that these cats and dogs who are being imported, often in very large groups, are going to be the largest risk for importation of New World screwworm into Vermont.”

New World screwworm arrived in the United States for the first time in 60 years in late spring. Since then, Levine said, “it’s one of the things we talk about every day.” The worm is the maggot form of a fly that feeds not on carcasses, but live tissue.

“This one will literally screw itself into living tissue and create larger wounds, which can be sources of infections and in some situations eat through to important vital organs,” Levine said.

In its emergency rule, the Agency of Agriculture acknowledged that the new requirements will “increase the cost of small animal importation.” But it said inaction “could have devastating economic consequences.” Levine said Vermont’s rule is part of a coordinated prevention effort among all New England states.

Leaders at the Central Vermont Humane Society support the new rule, even though it may slow down or even reduce the number of animals that rescue organizations can bring into the state.

“We don’t want dogs or cats to be the transportation unit for that to come into our state and impact our agricultural industry and livelihood,” said co-executive director Erika Holm. “And we also don’t want it here impacting our personal pets that we already have.”

Shelter pets coming into Vermont were already required to get certified veterinary inspections for other diseases and parasites, though those exams could occur within 30 days, according to Holm. She called screwworm a “gruesome infestation” that merits strong preventative measures.

Vermont’s lax regulatory regime for shelters and rescues means the Agency of Agriculture won’t know how many pets will actually receive the requisite examinations. Lisa Milot, director of the Division of Animal Welfare at the Department of Public Safety, said Vermont imports about 3,000 shelter pets annually through the rescues that self-report. But she said “there are definitely rescues that I don’t know are operating.”

“I have no idea right now of the scale and scope of those activities,” Milot said.

Legislation passed earlier this year will require all rescues in Vermont to register with the state; Milot said she’s in the process of getting that registration system operational. She said it could be the first step toward a stronger oversight system for animal rescues.