What is it that makes diseases caused by viruses and bacteria hard to treat?

Hello :) So here is some things i can use from my opinions and thoughts to help you with this question

So starting off with an exampleViruses are like hijackers. They invade living, normal cells and use those cells to multiply and produce other viruses like themselves. So you may ask how will this effect? This can kill, damage, or change the cells and make you sick. Different viruses attack certain cells in your body such as your liver, respiratory system, or blood.  When you get a virus, you may not always get sick from it. Your immune system may be able to fight it off.  For most viral infections, treatments can only help with symptoms while you wait for your immune system to fight off the virus. Antibiotics do not work for viral infections. There are antiviral medicines to treat some viral infections. Vaccines can help prevent you from getting many viral diseases.

explanation:

they can be good for the ecosystem

i think its the first one