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Bird flu has returned to the Midwest earlier than authorities expected after a lull of several months, with the highly pathogenic disease being detected in two commercial turkey flocks in western Minnesota and a hobby flock in Indiana, officials said Wednesday.

The Indiana State Board of Animal Health said Monday that laboratory testing of a commercial duck flock in Elkhart County has come back as presumptively positive for the virus.

Laboratory testing of a second commercial duck flock in Elkhart County came back as presumptively positive for the virus, the Indiana State Board of Animal Health said.

Laboratory testing of a commercial duck flock in Elkhart County has come back as presumptively positive avian influenza. So far this year, the virus has been confirmed in 24 states affecting chickens and turkeys.

The spread of a bird flu that is deadly to poultry raises the grisly question of how farms manage to quickly kill and dispose of millions of chickens and turkeys.

Nearly 7 million chickens and turkeys in 13 states have been killed this year due to avian influenza, prompting officials and farmers to acknowledge that, despite their best efforts, stopping the disease from infecting poultry is incredibly difficult.

Laboratory testing of a fourth commercial turkey flock in Dubois County has come back as presumptively positive for the virus, the Indiana State Board of Animal Health said. The samples are being verified at the U.S. Department of Agriculture’s National Veterinary Services Laboratory in Iowa.

Avian influenza has been detected in a fourth commercial poultry flock in southern Indiana, state officials said Saturday.

A strain of avian flu has been found at a third commercial turkey farm in southern Indiana, state officials said Thursday.