Some of these small parasites have been mutating and are now resistant to many over-the-counter medications.
In 1863, 150 years ago, Union and Confederate forces settled into camps just outside a small town in Pennsylvania named Gettysburg.
From July 1st to July 3rd they fought, and at the end of three days, the casualty count was more than 51,000.
Over the next few days, thousands of tourists will visit the Gettysburg National Military Park, to learn about the battles there and take in the events the park is holding to remember what happened there.
“The next time you go to a large football game, or large basketball game, look at the stands around you, because that’s about equal to the number that were lost,” park historian John Heiser told Here & Now.
But how do you balance tourism and respectful remembrance of one of the bloodiest moments in American history?
One way the park aims to do that is by not staging reenactments.
“We sponsor ‘living history’ programs on the battlefield — these are volunteers who come dressed as Union and Confederate soldiers and are very much experts in the field of what soldier life was during the Civil War,” Heiser said. “But we don’t sponsor opposing units, opposing fire, on hallowed ground.”