Finally, a bit of optimistic bird flu news.

No new flu cases were reported this week in Minnesota, and only one small outbreak occurred in Iowa, giving the poultry industry hope that the heat is quashing the virus at least until fall.

“We’re cautiously optimistic this could be a long break,” said Dr. Bill Hartmann, chief veterinarian for the Minnesota Board of Animal Health.

Meanwhile, two Minnesota turkey growers this week became the first to restock their stricken farms with healthy birds, and more such repopulations are expected in the coming weeks.

Also, the U.S. Department of Agriculture is expected Monday to release its first epidemiological report on the lethal flu that’s killed 47 million birds in 21 states, mostly commercial poultry.

The H5N2 bird flu that’s roared through Minnesota since early March has claimed 9 million turkeys and egg-laying chickens, part of the worst ever U.S. avian influenza outbreak. Only Iowa — where 29.1 million birds have died, mostly chickens — has been hit harder than Minnesota.

Iowa on Monday reported that a back-yard flock of 3,800 mixed birds had been hit by the flu, but that was the only case there this week. Minnesota’s last case was reported on June 5.

“I’m very encouraged,” said Steve Olson, executive director of the Minnesota Turkey Growers Association. “We’ve got a ways to go, but we’ve seen progress.”

The first Minnesota turkey farm hit by the flu — a 44,000-bird operation in Pope County — was the first to be repopulated with turkeys earlier this week. A second turkey grower began restocking Friday in Stearns County.

The flu leaves a grower with barns full of dead ­poultry. Usually, the birds are composted over a 28-day period. Then, the barns are cleaned and disinfected. But growers must then wait another 21 days before they can restock, and must get approval from the USDA and state animal health regulators.

Minnesota went from May 15-25 without any new bird flu cases, but then 18 new cases surfaced. Scientists believe warmth kills the flu virus, and the temperature has been climbing into the 80s and even 90s over the past week or so.

The flu is believed to originate in migrating waterfowl that don’t get sick, but shed the virus in their feces. When waterfowl migrate south, the pattern could be repeated this fall.

How exactly the flu has invaded so many farms — 108 in Minnesota alone — has been a mystery. The USDA may shed some light Monday with the release of a report on the outbreak.

The USDA discussed the report Friday with state veterinary officials including Hartmann. The agency has “identified that biosecurity is going to be very important,” he said.

The flu already blew through poultry farmers’ efforts to defend their operations from disease. But vigilance has been increased and improvements have been made, Olson said. One is a “Danish entry system” to barns, in which workers change clothes before actually setting foot in the barn, he said.

The report is expected to say that the flu may be creeping into barns by attaching itself to dust and traveling airborne for short distances, Olson said. Such a theory has been floated for the past ­several weeks.

Of the USDA report, Olson said, “I don’t expect any silver bullets.”