Japanese encephalitis

Test code: S0062 - Ultrasensitive qualitative detection of Japanese encephalitis virus by reverse transcription real time polymerase chain reaction

One of the leading causes of acute encephalopathy in children in the tropics is Japanese encephalitis (JE). An arbovirus, the Japanese encephalitis virus is transmitted by Culex mosquitoes and is a member of genus Flavivirus of the family Flaviviridae. The RNA genome of the JE virus is positive sense, single-stranded, approximately 11 Kb in length, and contains one long open reading frame.

JE virus is related to Murray Valley encephalitis virus. The virus is neurotropic and predominately affects the thalamus, anterior horns of the spinal cord, cerebral cortex, and cerebellum. It mainly affects children <15 years of age and is mostly asymptomatic. The occasional symptomatic child typically presents with a neurological syndrome characterized by altered sensorium, seizures, and features of intracranial hypertension. Though no antiviral drug is available against JE, effective supportive management can improve the outcome. Control of JE involves efficient vector control and appropriate use of vaccines.

Horses and primates can develop similar pathological lesions to those in human when infected with JE virus; they are considered dead-end hosts for JE. Most horses infected by JE virus show mild clinical signs, including fever, anorexia and depression. However, the mortality rate is high when JE infected horses show neurological symptoms (Ihara et al., 1997). Seroepidemiological survey of Asian monkeys has also shown widespread infection of these primates with JE virus (Yuwono et al., 1984). The virus can also infect birds, pigs and donkeys. Currently, the virus is mainly detected in East Asia, southeast Russia, India, Papua New Guinea and the Torres Strait Islands.

Conventional methods of JE diagnosis, including hemagglutination-inhibition and complement fixation tests for antibody assay, have been ineffective because of low sensitivity. Although a new immunoassay was developed to detect earlier, virus-specific IgM antibodies in the serum and cerebrospinal fluid (CSF) of acute and convalescent-phase patients, this new assay also suffered from low sensitivity and non-specific reaction. Reverse transcription-polymerase chain reaction (RT-PCR) has been used to detect Flavivirus rapidly and specifically.

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of JE infection.
• Ensure that animal populations are free of JE virus
• Early prevention of spread of the virus
• Minimize personnel exposure to the virus
• Safety monitoring of biological products and vaccines that derive from horses and primates

References:
Ihara, T., Kano, R., Nakajima, Y., Sugiura, T., Imagawa, H., Izuchi, T. and Samjima, T. (1997) Detection of antibody to Japanese encephalitis virus (JEV) by enzyme-linked immunosorbent assay (ELISA). J. Equine Sci. 8: 25-28.
Yuwono, J., Suharyono, W., Koiman, I., Tsuchiya, Y. and Tagaya, I. (1984) Seroepidemiological survey on dengue and Japanese encephalitis virus infections in Asian monkeys. Southeast Asian J Trop Med Public Health. 15:194-20

Specimen requirements: 1 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or 1 ml CSF, serum, plasma or tissue, shipped overnight at room temperature; or 1 ml frozen serum, plasma, tissue or CSF, shipped frozen.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative reverse transcription real time PCR

Normal range: Nondetected