Tarrant County's first confirmed human West Nile virus case of 2026 is not the mild version. What Separates Neuroinvasive Disease From West Nile FeverMost people infected with West Nile never know it. Roughly one in five develop West Nile fever, which brings headache, fever, muscle and joint aches, nausea and fatigue. The newest confirmed fact is that Tarrant County's first human West Nile case of 2026 involves the severe neuroinvasive form, announced on July 24. What is neuroinvasive West Nile disease?