Diagnosis of nipah virus encephalitis by electron microscopy of cerebrospinal fluid.

Background: between 1998 and 1999, an outbreak of potentially fatal viral encephalitis erupted among pig farm workers in West Malaysia, and later spread to Singapore where abattoir workers were afflicted. Although Japanese encephalitis virus was initially suspected, the predominant aetiologic agent was subsequently confirmed to be Nipah virus, a novel paramyxovirus related to but distinct from Hendra virus. Objective: to describe a case of Nipah virus encephalitis in a pig farm worker from Malaysia. Study design: the clinical, laboratory and radiological findings of this patient were scrutinized. Special emphasis was placed on the electron microscopic analysis of the cerebrospinal fluid (CSF) specimen from this patient. Results: the neurological deficits indicative of cerebellar involvement were supported by the magnetic resonance imaging that showed prominent cerebellar and brainstem lesions. CSF examination provided further evidence of viral encephalitis. Complement fixation and/or RT-PCR assays were negative for Japanese encephalitis, herpes simplex, measles and mumps viruses. ELISA for detecting IgM and IgG antibodies against Hendra viral antigens were equivocal for the CSF specimen, and tested initially negative for the first serum sample but subsequently positive for the repeat serum sample. Transmission electron microscopy of negatively-stained preparations of CSF revealed enveloped virus-like structures fringed with surface projections as well as nucleocapsids with distinctive helical and herringbone patterns, features consistent with those of other paramyxoviruses, including Hendra virus. Conclusion: this case report reiterates the relevant and feasible role of diagnostic electron microscopy for identifying and/or classifying novel or emerging viral pathogens for which sufficiently specific and sensitive tests are lacking.