Two New World screwworm cases in dogs are among more than 30 confirmed instances in Texas and New Mexico, prompting warnings Wednesday from veterinarians and humane societies that pet owners need to remain vigilant to protect their animals.

The parasite reappeared in cattle in the U.S. in June, more than 50 years after it had been largely eradicated from the country.

The pest is actually the larvae of the New World screwworm fly.