Adoptions are on hold for thousands of dogs and cats in Texas, potentially putting the animals at risk of being euthanized, because of efforts to stop the spread of the New World screwworm, an insect that has crossed the border from Mexico into the United States for the first time in 60 years.

The flesh-eating parasite threatens the nation’s $113 billion beef industry, prompting federal officials to close the border to cattle movements. Because the screwworm also can infect pets, most states have restricted the movement of animals from infested areas of Texas, leading to crowded conditions in state shelters that rely on adoptions to other regions of the country.

“It’s thrown a wrench into things, for small rescues as well as the bigger shelters,” said Mia Bendixsen, executive director of the Texas Humane Legislation Network, which promotes animal welfare laws.

The screwworm can lay eggs that hatch into flesh-eating larvae in the wounds or mucous of any mammal, and of the dozens of infections in southern Texas and southeastern New Mexico, several have been in dogs. Forty-four states have restricted the movements of pets from infested areas, creating a hardship for shelters from Texas that typically send thousands of animals to other states each year.

In Corpus Christi, the Gulf Coast Humane Society couldn’t get rescued dogs into New York state for weeks, causing the shelter’s animal population to climb from around 325 to nearly 450.

The shelter, which sends about 500 dogs a year outside Texas, created more space in outdoor exercise areas until New York again allowed dogs from Texas — if a veterinarian first certified that each one wasn’t infected with the screwworm.

She added that if her shelter doesn’t have space to take animals from municipal shelters, “then they have to euthanize more animals.”