(AP) — Nebraska agriculture officials say another 1.8 million chickens must be killed after bird flu was found on a farm in the latest sign that the outbreak that has already prompted the slaughter of more than 50 million birds nationwide continues to spread.The Nebraska Department of Agriculture said Saturday that the state’s 13th case of bird flu was found on an egg-laying farm in northeast Nebraska’s Dixon County, about 120 miles (193 kilometers) north of Omaha, Nebraska..Just like on other farms where bird flu has been found this year, all the chickens on the Nebraska farm will be killed to limit the spread of the disease.In most past bird flu outbreaks the virus largely died off during the summer, but this year’s version found a way to linger and started to make a resurgence this fall with more than 6 million birds killed in September.Crowd angered by lockdowns calls for China's Xi to step downRussian rocket kills newborn in repeat attack on small townFrance takes 1st step to add abortion right to constitutionWHO, CDC: A record 40 million kids miss measles vaccine doseCommercial farms have taken a number of steps to prevent the virus from infecting their flocks, including requiring workers to change clothes before entering barns and sanitizing trucks as they enter the farm, but the disease can be difficult to control.Plus, any viruses will be killed by properly cooking poultry to 165 degrees Fahrenheit."