Because waste that is not disposed of properly has a chance to become a place that nasty bacteria can grow into large numbers and come in contact with humans and animals that get infected and carry their infection to other humans or animals.
Our bodies are not use to living with these nasty bacteria inside of us, so when we are infected the nasty bacteria stops our bodies functioning properly.
If our immune systems are weak we may not be able to fight off the nasty bacteria before it grows into a bigger problem by spreading through our body and making it even harder for our bodies to work normally.
This means that we can get very sick and possibly die if not treated.
So it's not the pests fault its the nasty bacteria they carry.
Our bodies are not use to living with these nasty bacteria inside of us, so when we are infected the nasty bacteria stops our bodies functioning properly.
If our immune systems are weak we may not be able to fight off the nasty bacteria before it grows into a bigger problem by spreading through our body and making it even harder for our bodies to work normally.
This means that we can get very sick and possibly die if not treated.
So it's not the pests fault its the nasty bacteria they carry.