We have lost three chickens in our flock since late October. I am not sure if the cause of death was the same, but I am assuming so since all seemed to have the same symptoms. We had two chickens (4 years old) who seemed in perfect health. I discovered our Barred Rock one afternoon collapsed in a heap. She was alive but having respiratory trouble, was weak and could barely move. She was dead the next morning. We had a heatwave so I thought it was perhaps dehydration. It came on suddenly and she was gone in less than 24 hours. Our Australorp seemed perfectly healthy so we added two pullets to our flock. The farm where we purchased the new pullets (and our original flock) had suggested sending our Barred Rock to UC Davis for a necropsy. Unfortunately we had already disposed of her remains. Six weeks after our Barred Rock died I found our Australorp in the same condition. Limp, heavy breathing. She was gone, again in less than 24 hours and unfortunately something attacked her in the middle of the night so we were unable to send her in for the necropsy. But the two new pullets were perfectly healthy and growing. Eight weeks after our Australorp passed the same thing happened to one of our pullets. When she passed I sent her remains in for a necropsy and we just received the results: Avian sarcoma leukosis virus. How can I find out of our last remaining pullet is infected. She seems in good health. We have removed all of the shavings and done a thorough bleach cleaning of the coop but I don't want to add new pullets to the flock if this virus will continue to infect our flock. Is it contagious? How can I prevent this from happening to our remaining and future hens?