Complex sentence: Nephropathia epidemica is a virus-infection caused by the Puumala virus, and it has a sudden onset with fever, headache, backpain and gastrointestinal symptoms, but sometimes worse symptoms such as internal hemorrhaging and it can even lead to death.
Split into simpler sentences: Nephropathia epidemica is a virus-infection caused by the Puumala virus. It has a sudden onset with fever, headache, backpain and gastrointestinal symptoms, but sometimes worse symptoms such as internal hemorrhaging and it can even lead to death.