Meningitis is a disease that primarily affects the brain. Option 1, which suggests that meningitis affects the kidneys, is incorrect. Meningitis is an inflammation of the meninges, which are the protective membranes covering the brain and spinal cord. Therefore, it mainly targets the central nervous system, including the brain. Option 2, which states that meningitis affects the liver, is also incorrect. The liver is not directly involved in the disease. Option 3, stating that the heart is affected by meningitis, is incorrect as well. The heart is a separate organ and is not directly affected by this condition. So, the correct answer is option 4, which correctly identifies the brain as the main organ affected by meningitis.