Rats usually spread a disease when they bite a person and can give a person rat bite fever.
The urine of rats can also spread the disease leptospirosis which can lead to kidney and liver damage and even failure.
Other diseases that can be spread by rats are, Lymphocytic Chorio-meningitis (LCM), Omsk Hemorrhagic Fever, Plague, Hantavirus Pulmonary Syndrome, Hemorrhagic Fever with Renal Syndrome and Lassa Fever.