(The Center Square) – The number of avian influenza cases in Montana has increased to at least 16 this year, state officials announced.

Montana Department of Livestock officials say the Highly Pathogenic Avian Influenza was responsible for killing a “small backyard poultry flock” in Flathead County. 

“HPAI has impacted over 80,000 domestic birds in Montana,” Montana State Veterinarian Martin Zaluski said. “The impacts of this year’s disease outbreak are substantial.”

The outbreak in Montana began in March, and authorities say the HPAI variant has killed more than 56 million birds in 47 states. Migratory waterfowl are believed to be the main cause for the spread, according to officials. The virus is transferred through feces, saliva, and respiratory secretions. 

“Domestic poultry become infected through direct contact with wild birds, or through contact with contaminated objects, equipment, or the environment,” MDOL said. 

MDOL said bird owners can protect flocks by preventing contact between wild or migratory birds and domestic poultry, as well as keeping house birds indoors. 

“Sick birds can exhibit numerous signs such as swollen eyes, discolored comb and legs, a significant drop in egg production, or decrease in water and feed consumption,” MDOL said. “However, the most common sign has been sudden death of multiple birds within a flock.”

More information is available on the Montana Department of Livestock’s website, as well as the Centers for Disease Control and Prevention.