Trench fever is a sickness caused by tiny little creatures called bacteria. Bacteria are really small and you can't see them without a microscope. These bacteria live inside a bug that likes to bite people called a louse. A louse is also really small and can't fly like a butterfly.
Trench fever mostly affected soldiers who were fighting in a war a long time ago. Soldiers would spend a lot of time in muddy, dirty trenches which were like really deep holes they made to keep safe from the enemy. The lice would crawl on the soldiers and bite them and that's how they would get sick with trench fever.
When you have trench fever, you may not feel well and have a fever, which is when your body gets hotter than usual. You might have bone pain too, which is when it feels like someone is squeezing your bones really tight. You might also feel really tired and have a headache. But don't worry, doctors can give you medicine to feel better!
Nowadays, trench fever doesn't happen as much because soldiers don't spend as much time in dirty, muddy trenches. But it's still really important to make sure you stay clean and away from lice because they can still make you sick. And if you ever feel like you are sick or have a fever, tell a grown-up so you can go see a doctor to get better.