Illustration: David Macaulay In February 2024, dairy farmers in the northwest corner of the Texas Panhandle noticed that their herds were getting sick. A cow’s temperature would spike, and she would stop eating. Soon, her milk would dry up or turn thick — tests would reveal the milk had twice the normal number of white blood cells. The feverish cows would barely drink any water. As they grew dehydrated, their eyes sank into their heads. Nearly all of them had mastitis: a swollen, painful udder