It's critical that medical staff keep a diligent eye out for signs that soldiers are suffering from the effects of biological weapons, which use bacteria and viruses to infect troops with disease. They're especially dangerous because infection can sometimes spread from one infected soldier to another. Diseases like smallpox and pneumonic plague can cause massive damage to troops if doctors don't catch and treat them early. Even with treatment, soldiers could die from their effects.
Army doctors rely on reports from the Centers for Disease Control and Prevention and the Department of Defense to get a feel for what biological weapons they may be facing, if any. If there's a risk of a biological attack, they do what they can to prevent illness or at least limit its spread. It's critical in situations like this to find the outbreak's source, because early detection can save lives.
As we'll see next, life in the field is hard, and Army doctors work to treat and prevent pain so that soldiers can do their jobs.