12 y/o healthy male with altered mental status. H/o 2 days of vomiting, slurred speech, headache, progressing to altered sensorium. No seizures/rash. H/o camping in East Texas 1-week ago; playing with dogs at home. No diving in lakes/tick bites/cats/farm-animals. Patient had received all age appropriate vaccines. O/E, comatose, febrile at 39.5C. Pupils minimally reactive, gag reflex absent, hypotonic with diminished DTRs. Meningeal signs absent. MRI brain:left thalamus edema (Figure1). Differential Diagnosis: Viral Encephalitis: HSV, Enteroviruses, Arboviruses, Influenza Rickettsial neuroinvasive disease Amoebic Encephalitis Mycoplasma encephalitis NMDA receptor antibody encephalitis Diagnostic Results: CSF and serum testing negative except serum for West Nile virus IgM+. Repeat testing after a week: serum West Nile virus IgM and serum West Nile virus IgG+ Course: Patient received IVIG after second serology. Sensorium improved however, progressed to flaccid quadriplegia with MRI consistent with poliomyelitis, which gradually improved. (Figure 2). Discussion: WNV is ssRNA flavivirus, isolated in 1937 in West-Nile district Uganda, transmitted through Culex mosquito bites with birds as reservoirs (300 species). About 1/3 of all cases reported from Texas in recent years. 80% asymptomatic, 20% develop West Nile fever. West Nile Neuroinvasive disease (WNND) in < 1%: meningitis in 25-35%, encephalitis in 60-75%, poliomyelitis in 5-10%. WNV encephalitis is rare in children. WN poliomyelitis affects all ages unlike encephalitis (affects elderly) and occurs in isolation or with meningoencephalitis. Pathogenesis related to pure motor deficit due to involvement of anterior horn cells. Per CDC, WNV IgM antibody in serum within 8-14 days or CSF within 8 days of onset is diagnostic. CSF PCR lacks sensitivity. MRI usually normal, however, abnormalities in thalamus, basal-ganglia, spinal-cord can be seen. Case-fatality rate for WNND in children is <1%; in adults over 10%. WNV Poliomyelitis has the worst prognosis, with strength recovery usually occurring within first 6-8 months followed by subsequent plateau. Management is supportive with unproven role of interferon, anti-WNVIG, IVIG. No vaccine is available and primary prevention is mosquito control.