title: West Nile encephalitis outbreak in Kerala, India, 2011.
abstract: BACKGROUND
  An outbreak of acute encephalitis syndrome (AES) was reported in Kerala in India in May 2011. The outbreak features were unusual in terms of seasonality, geographical distribution, age group, and clinical manifestations in comparison to the epidemiological features of Japanese Encephalitis.
  
  
  OBJECTIVE
  To detect the etiology of the acute encephalitis syndrome outbreak.
  
  
  METHODS
  Investigation of outbreak was undertaken by collection of brief clinical history and epidemiological details along with the specimens for viral diagnosis. The serum/CSF samples (patients=208) received from the sentinel hospitals were subjected to IgM capture ELISA and RT-PCR specific for Japanese encephalitis (JE) virus and West Nile virus (WNV). The JE/WN IgM positive samples were further tested by serum neutralization assay for the presence of JE and WNV specific neutralizing antibody.
  
  
  RESULTS
  Most of the affected patients were aged above 15 years. No spatial clustering of the disease was noticed. Cases were observed in premonsoon and early monsoon season and in JE non-endemic area of Kerala. A total of 47 patient samples were positive for in-house JE IgM capture ELISA and WNV IgM capture ELISA. Serum neutralization assay result revealed that 32 of 42 (76.19%) sera were positive for WNV neutralization antibodies. WNV was isolated from a clinical specimen. Phylogenetic analysis of WNV envelope gene revealed 99% homology with Russian Lineage 1 WNV.
  
  
  CONCLUSIONS
  West Nile virus (WNV) etiology was confirmed by virus isolation and detection of virus specific antibody from clinical specimen. Phylogenetic analysis grouped the current strain in lineage I West Nile virus.
authors.affiliation: National Institute of Virology, Kerala, Govt. T. D. Medical College Hospital, Alappuzha 688005, Kerala, India. Electronic address: anukumar74@gmail.com.
authors.forename: B
authors.initials: B
authors.lastname: Anukumar
authors.affiliation: National Institute of Virology, 20-A, Dr. Ambedkar Road, Post Box No. 11, Pune 411001, Maharashtra, India. Electronic address: gajanansapkalniv@gmail.com.
authors.forename: Gajanan N
authors.initials: GN
authors.lastname: Sapkal
authors.affiliation: National Institute of Virology, 20-A, Dr. Ambedkar Road, Post Box No. 11, Pune 411001, Maharashtra, India. Electronic address: drtandale@gmail.com.
authors.forename: Babasheb V
authors.initials: BV
authors.lastname: Tandale
authors.affiliation: National Institute of Virology, Kerala, Govt. T. D. Medical College Hospital, Alappuzha 688005, Kerala, India. Electronic address: balasniv@gmail.com.
authors.forename: R
authors.initials: R
authors.lastname: Balasubramanian
authors.affiliation: National Institute of Virology, 20-A, Dr. Ambedkar Road, Post Box No. 11, Pune 411001, Maharashtra, India. Electronic address: dayapavitrakar@gmail.com.
authors.forename: Daya
authors.initials: D
authors.lastname: Gangale
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D057134:Antibodies, Neutralizing / Q000097:blood; D000914:Antibodies, Viral / Q000097:blood; D002555:Cerebrospinal Fluid / Q000821:virology; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D004196:Disease Outbreaks; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood; D007194:India / Q000453:epidemiology; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics / Q000302:isolation & purification; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014759:Viral Envelope Proteins / Q000235:genetics; D014766:Viremia; D014901:West Nile Fever / Q000453:epidemiology*; D014902:West Nile virus / Q000276:immunology / Q000302:isolation & purification*
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D007075:Immunoglobulin M; D012367:RNA, Viral; D014759:Viral Envelope Proteins
keywords: Acute encephalitis syndrome; Disease outbreak; Flavivirus; India; Kerala; Lineage I West Nile virus