Emergence of human West Nile Virus infection in Sri Lanka
Lohitharajah et al. BMC Infectious Diseases
Emergence of human West Nile Virus infection in Sri Lanka
Janarthani Lohitharajah 3
Gathsaurie Neelika Malavige 2
Anthony Jin Shun Chua 1
Mah Lee Ng 1
Carukshi Arambepola 4
Thashi Chang 0
0 Department of Clinical Medicine, Faculty of Medicine, University of Colombo , 25, Kynsey Road, Colombo 08 , Sri Lanka
1 Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore , Singapore, Singapore
2 Department of Microbiology, Faculty of Medical Sciences, University of Sri Jayawardenapura , Sri Jayawardenapura , Sri Lanka
3 Faculty of Medicine, University of Colombo , Colombo , Sri Lanka
4 Department of Community Medicine, Faculty of Medicine, University of Colombo , Colombo , Sri Lanka
Background: West Nile virus (WNV) has emerged as one of the most common causes of epidemic meningoencephalitis worldwide. Most human infections are asymptomatic. However, neuroinvasive disease characterized by meningitis, encephalitis and/or acute flaccid paralysis is associated with significant morbidity and mortality. Although outbreaks have been reported in Asia, human WNV infection has not been previously reported in Sri Lanka. Methods: Sera and cerebrospinal fluid (CSF) from 108 consecutive patients with a clinical diagnosis of encephalitis admitted to two tertiary care hospitals in Colombo, Sri Lanka were screened for WNV IgM antibody using enzyme-linked immunosorbent assay. Positive results were confirmed using plaque reduction neutralization test (PRNT). Patient data were obtained from medical records and by interviewing patients and care-givers. Results: Three of the 108 patients had WNV IgM antibody in serum and one had antibody in the CSF. The presence of WNV neutralizing antibodies was confirmed in two of the three patients using PRNT. Two patients had presented with the clinical syndrome of meningoencephalitis while one had presented with encephalitis. One patient had CSF lymphocytic pleocytosis, one had neutrophilic pleocytosis while CSF cell counts were normal in one. CSF protein showed marginal increase in two patients. Conclusions: This is the first report of human WNV infection identified in patients presenting with encephalitis or meningoencephalitis in Sri Lanka. There were no clinical, routine laboratory or radiological features that were distinguishable from other infectious causes of meningoencephalitis.
West Nile virus; Encephalitis; Meningoencephalitis; Sri Lanka
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Background
West Nile virus (WNV) is one of the most widely
distributed, medically important arboviral infections that
has caused major outbreaks in many parts of the world
[1]. Although the initial WNV outbreaks were confined
to rural areas in Africa [1], it is now the leading cause of
encephalitis in USA, Europe and Australia [2, 3]. Initial
WNV outbreaks were associated with only a few cases
of severe neurological diseases. However, neuroinvasive
disease is now more frequent and the case fatality rates
range from 4.2 to 18.6 % in more recent epidemics [1, 4, 5].
WNV is considered to be one of the most important
emerging flaviviral infections in the world, due to the
increase in the number of cases with expansion in
geographical distribution, and its association with severe
neurological disease [6, 7].
WNV is a zoonotic infection, where the virus cycles
between mosquitoes and birds. The Culex genus of
mosquitoes are the main vectors while passerine birds act as
amplifying hosts [1]. Humans and mammals are usually
incidental, dead-end hosts as viral titers in mammals are
insufficient to infect mosquitoes for further transmission
to other mammals [8]. WNV results in neuroinvasive
disease in less than 1 % (approximately 1 in 150) of
infected individuals, while asymptomatic infections occur
in around 80 % [9, 10]. Approximately 20 % of infected
individuals develop WN fever, which is an
undifferentiated flu-like illness that occurs 2–14 days after an
infectious mosquito bite. This is characterized by fever,
myalgia, gastrointestinal symptoms and sometimes a
macular-papular rash [9]. WN fever may mimic the
clinical syndromes of other flavivirus infections such as
dengue fever. WNV neuroinvasive disease manifests as
meningitis, encephalitis, asymmetric acute flaccid paralysis
or a mixed pattern of these syndromes. Encephalitis is
more common than meningitis in older age groups, and is
commonly associated with extrapyramidal features while
acute flaccid paralysis may lead to respiratory paralysis.
After the acute infection, many patients experience
persistent symptoms, such as fatigue, memory impairment,
weakness, headache, and balance problems.
Encephalitis is a notifiable disease in Sri Lanka and
annually, 165–220 cases are reported to the Epidemiology
Unit of Sri Lanka. However, in 2013, a large outbreak of
encephalitis occurred with 141 cases of encephalitis
being reported in the first 2 months of the year. Although
cases of enceph (...truncated)