Treatment of West Nile Virus With MGAWN1

Inclusion Criteria: 1. Provide written informed consent 2. Be \>=18 years of age at the time of enrollment 3. Have West Nile Fever defined as: 1. temperature \>38°C, headache, AND 2. positive diagnostic test for WNV Ribonucleic acid or Immunoglobulin M with serum or cerebrospinal fluid (CSF) OR have West Nile Neuroinvasive Disease (includes neurological signs and/or symptoms of West Nile meningitis, encephalitis, and/or acute flaccid paralysis), defined as: • West Nile encephalitis (must meet criteria a and b below) 1. Encephalopathy (depressed or altered level of consciousness, lethargy, or personality change lasting 24 hours) 2. CSF pleocytosis \>=5 cells/mm\^3 AND/OR • West Nile meningitis (must meet criteria c and d) 3. Clinical signs of meningeal inflammation, including nuchal rigidity, Kernig or Brudzinski sign, photophobia, or phonophobia 4. CSF pleocytosis \>=5 cells/mm\^3 AND/OR • Acute flaccid paralysis (must meet criteria e and f) 5. Acute onset of limb weakness with marked progression over 48 hours 6. Two or more of the following conditions: * asymmetry to weakness * areflexia or hyporeflexia of affected limb(s) * absence of pain, paresthesia, or numbness in affected limb(s) * CSF pleocytosis \>=5 cells/mm\^3 * CSF elevated protein levels (4.5 g/L) * electrodiagnostic studies consistent with an anterior horn cell process * or abnormal increased signal in the anterior gray matter as documented by spinal cord magnetic resonance imaging 4. Have epidemiological factors consistent with West Nile Virus infection (must meet criterion a or b below): 1. Appropriate time of year for West Nile Virus transmission in region 2. Travel history to a region where West Nile Virus is active 5. Develop signs and/or symptoms within 14 days before study enrollment. 6. If female of childbearing potential or male and in a sexual relationship with a female of childbearing potential, agree (or have partner agree) to practice abstinence or use 2 of the following methods of contraception for 120 days (approximately 4 months) after study drug administration: 1. Oral contraceptives, or other form of hormonal birth control including hormonal vaginal rings or transdermal patches 2. An intrauterine device 3. Barrier contraception (condom) with a spermicide (i.e., female subject ensures use by male partner\[s\]) 4. Any other equivalent method of contraception (as judged by the investigator)