Complex sentence: Headache can be a prominent symptom of WNV fever, meningitis, encephalitis, menigoencephalitis and it may or may not be present in poliomyelytis-like syndrome thus headache is not a useful indicator of neuroinvasive disease.
Split into simpler sentences: Headache can be a prominent symptom of WNV fever, meningitis, encephalitis, menigoencephalitis, and it may or may not be present in poliomyelytis-like syndrome. Thus, headache is not a useful indicator of neuroinvasive disease.