DES MOINES, Iowa — Two top veterinary officials with the U.S. Department of Agriculture and farmers affected by the bird flu outbreak said Tuesday it will take increased surveillance, improved farm security and more money to fight off a possible fall return of the disease that devastated chicken and turkey flocks.

The U.S. Senate Agriculture Committee held a livestreamed hearing to discuss the response to the outbreak that has killed 48 million birds since early March in 15 states, including hardest-hit Iowa, Minnesota and Nebraska.

With no new outbreaks in three weeks, it appears the virus has been eradicated for now, said Dr. David Swayne, director of a USDA poultry research laboratory in Georgia.

He joined John Clifford, the deputy administrator of veterinary services for the Animal and Plant Health Inspection Service at USDA, in discussing the outbreak and how the government is prepared to handle a possible recurrence.

The government believes waterfowl carry the virus and dropped it over Midwestern farms during the spring migration north. Hotter, dryer weather kills the virus, but scientists worry it could return with cooler fall weather and the southward migration.

The USDA has prepared for an unlikely worst-case scenario, Clifford said, developing a plan robust enough to handle cases at up to 500 farms in all 20 states with major poultry flocks.

The government has increased surveillance of wild birds to see where the virus is present and is working with industry groups to establish improved biosecurity, including controlling movement of staff between barns, cleaning equipment more thoroughly and training personnel on how the virus spreads, according to the officials’ testimony.

One reason the virus spread so quickly was it took too long to euthanize the millions of sick birds who had flu, which made spreading more likely, Clifford said.

The government hired contractors to suffocate turkeys with foam or use a gas to asphyxiate chickens. At the beginning of the outbreak, crews couldn’t keep up.

Brad Moline, a turkey farm owner from Manson, Iowa, testified that he lost 56,000 turkeys and two-thirds of his income for the year. He said some of the government’s hired contractors were not property trained, and the USDA failed initially to communicate steps farmers needed to take to prevent spread of the virus.

Clifford said the agency learned from the those issues to implement the new policies.