Laboratory techniques for human viral encephalitis diagnosis

Encephalitis is an inflammatory process involving the parenchyma of the brain. It typically presents as a clinical syndrome characterised by fever, headache and altered conscious level, often with focal neurological deficits and fits. The clinical presentation overlaps with other diseases of the central nervous system including viral and bacterial meningitis, and brain abscess. The causes of encephalitis are legion, and include principally viral but also bacterial, parasitic and fungal pathogens. Noninfectious aetiologies, especially autoimmune conditions such as potassium channel voltage gated antibodies and anti-NDMA receptor antibodies, are increasingly recognised. Diagnosis comes from clinical examination, neuroimaging and laboratory testing. With such a wide range of potential pathogens a syndromic approach to diagnosis is preferred, testing for a range of organisms. Traditional techniques such as cell culture and direct virus antigen detection have little or no role nowadays. Laboratory diagnosis of viral encephalitis is ideally based on examination of cerebrospi-nal fluid (CSF) for cells, protein and glucose, followed by nucleic acid amplification tests (NAAT) such as polymerase chain reaction (PCR) for a range of viral targets. Samples other than CSF sometimes give a definitive or probable aeti-ological diagnosis; examples include skin biopsy in rabies, and serum NAAT and antibody tests for some arboviruses and enteroviruses. Newer approaches to amplification and to multitarget detection are becoming increasingly important. Detection of intrathecal antibody production against specific viruses retains a place in diagnosis where NAAT is negative. Some of the laboratory techniques available will be discussed in this article.