west nile encephalitis is a mosquito - borne disease endemic to africa , asia , australia , and europe and the west nile virus is a single - stranded rna virus which belongs to the japanese encephalitis serogroup of flaviviruses ( 1 ) . it could be accompanied with various neurologic symptoms and signs including headache , mental confusion , optic neuritis , and muscle weakness ( 2 , 3 , 4 ) . after the first two cases of west nile encephalitis were diagnosed in 1999 in new york ( 5 ) , many neurological abnormalities were noted in patients of west nile encephalitis , and the flaccid muscle weakness is a distinctive feature of this disease ( 2 , 3 , 6 ) . until now , west nile encephalitis was never diagnosed in korea , and it is the first report of west nile encephalitis in korea . a 58-yr - old man was admitted with headache for 2 months in june 2012 . the patient had been on a business trip in guinea , west africa since 7 months ago . he denied other symptoms such as nausea , vomiting , neck stiffness , and dizziness . the headache and cognitive impairment had been worsening and accompanied general weakness and weight loss 10 kg for 2 months . he had no hypertension , cardiac diseases , chronic renal disease , and liver disease . he had a 20 pack - year history of smoking and no recent alcohol intake . the patient denied using any medications except for antimalarial drug ( sulfadoxine 500 mg , pyrimethamine 25 mg , artemether 80mg / ml ) and analgesics in africa . at admission to our hospital , he was afebrile ( 36.4 ) and his vital signs were blood pressure 121/78 mmhg , heart rate 97/min , and respiratory rate 20/min with normal findings of physical examinations . findings on initial neurologic examinations were normal except minimental state examination ( mmse ) with score 20 . admission complete blood count revealed hemoglobin of 12.7 g / dl , leukocyte count of 16.2  10/l with 79% neutrophils , and a platelet count of 388  10/l . the patient 's calcium level , chemistries , and liver function tests were normal and crp was slightly increased . analysis of cerebrospinal fluid ( csf ) demonstrated 0 rbc/l , 214 wbcs/l ( with 80% lymphocytes and 12% neutrophils ) , a protein level of 161.9 mg / dl , a glucose level of 93 mg / dl and ada level of 4.8 . a brain magnetic resonance imaging ( mri ) revealed multifocal patchy t2 high signal lesions in both temporal lobes , basal ganglia , internal capsule posterior limb , and corona radiata , which suggested encephalitis . electroencephalogram showed frequent semirrhythmic medium amplitude delta slowing on both hemispheres , with frontal dominancy . on hospital day 1 , his body temperature was 38.0 and malaria test was negative . follow up csf tapping was done on hospital day 3 and 6 rbc/l , 340 wbcs/l ( with 67% neutrophils and 28% lymphocytes ) , a protein level of 164.6 mg / dl , a glucose level of 70 mg / dl and ada level of 6.0 . the patient complained of both leg weakness and the motor strength of bilateral lower extremity was 4+/4 + . he also complained of both leg pain and paresthesia , deep tendon reflex on both lower extremities were areflexia . there was no remarkable finding on nerve conduction study ( ncs ) and needle electromyogram ( emg ) , but arachnoiditis and myelitis were observed on lumbar spine mri ( fig . polymerase chain reactions ( pcr ) for hsv , vzv , ebv , cmv , enterovirus , tuberculosis , and mycoplasma pneumonia were negative in csf . serological test for brucellosis , lyme disease , leptospirosis , hantann virus and tsutsugamuchi disease were negative at admission an additional serological study for specific antibody for west nile virus was done , the total antibody titer of west nile virus was 1:337 , and follow up titer after 2 weeks was 1:1,632 in serum by plaque reduction neutralization test . treatment with interferon- 3mu was started and maintained for 2 weeks . follow up csf tapping was done after one month later and 9 rbc/l , 9 wbcs/l ( with 16% neutrophils and 67% lymphocytes ) , a protein level of 99.9 mg / dl and a glucose level of 66 mg / dl . encephalitis with severe muscle weakness is a common symptom and may provide a diagnostic clue . to confirm a diagnosis , it needs identification of west nile virus in serum or csf . igm antibody is usually detectable only during a few days of illness ( 7 ) . another method is the identification of a change by a factor of four or more in the antibody titer or virus - neutralization tests ( 7 ) , the case was positive for the virus - neutralization tests . serological test and pcr for other infectious agents were all negative and autoimmune encephalitis such as nmda receptor encephalitis was excluded by clinical symptoms ( 8) . many studies indicated that the weakness was probably caused by infection and inflammation in the anterior horn cells of the spinal cord and brainstem like poliomyelitis ( 6 , 9 , 10 ) . electrophysiologic studies showed reduced compound muscle action potentials , and normal sensory nerve action potentials , which is distinguished from guillain - barre syndrome ( 3 , 6 , 9 , 10 ) . a few autopsy studies demonstrated that the inflammatory changes with severe leukocytic inflammation of the anterior horns with striking loss of motor neurons ( 4 , 11 ) . but this case did not present any abnormalities in the electrophysiologic study . he complained about severe sensory symptoms with leg pain and arachnoiditis was observed in lumbar mri . only a few reports noted a caudal equine enhancement ( 4 ) and weakness due to acute radiculitis ( 12 ) . it 's hard to say that his weakness was caused by only radiculopathy , because paralysis of the west nile encephalitis generally results from anterior horn cell damage . but in this case , radiculopathy also contributes the motor weakness of the west nile encephalitis . at present there is no established treatment for west nile encephalitis and basic treatment is a supportive care . but because it 's a fatal disease , sometimes it was treated with plasmapheresis or administration of iv immunoglobulin ( 5 ) . interferon- has been reported to inhibit west nile virus replication , and some successful cases were reported using of interferon- to treat west nile encephalitis ( 13 ) . korea is not an endemic area of west nile virus , but an increasing overseas trip poses a risk of the influx of overseas diseases and may contribute to the global spread of infectious diseases .
west nile encephalitis was first identified in 1937 , but until now , it was never diagnosed in korea . 
 a 58-yr - old korean man was admitted with headache and cognitive dysfunction . 
 the patient had been on a business trip in guinea . 
 cerebrospinal fluid ( csf ) showed pleocytosis . 
 the patient complained of both leg weakness , and arachnoiditis and myelitis were observed on lumbar magnetic resonance imaging ( mri ) . 
 a specific neutralizing antibody for west nile virus was positive in serum . 
 after a treatment with interferon- 3mu , follow up csf findings recovered completely after 3 months later . 
 the first case of west nile encephalitis in korea was imported from guinea , and was cured successfully.graphical abstract