St. Louis Encephalitis

Test code: S0057

Test name: Ultrasensitive qualitative detection of St. Louis Encephalitis virus by reverse transcription real time polymerase chain reaction

West Nile (WN) and St. Louis encephalitis (SLE) viruses are both arthropod-borne viruses within the Japanese encephalitis virus serocomplex (Murphy et al., 1995). They belong to the family Flaviviridae, genus Flavivirus. This group of viruses possesses a single positive strand of RNA genome of approximately 11 kb. Like West Nile virus and Japanese encephalitis virus, SLE is transmitted primarily through Culex species mosquitoes and birds. Humans, primates and other mammals are thought to be incidental hosts (Monath and Heinz, 1996).

Unlike WN, endemic SLE virus transmission in nature is silent, with no reports of avian mortality. Nevertheless, significant endemic spread of SLE in United States and in several South American countries has been reported. Over the past 70 years, SLE virus has been responsible for numerous epidemics throughout the United States; the largest occurred in 1975, with approximately 2,000 cases reported (Monath and Heinz, 1996).

Detection of this SLE virus by virus isolation followed by identification through immunofluorescence assays can take over a week to complete. Immunoglobulin M (IgM) capture and IgG enzyme-linked immunosorbent assays (ELISAs) are also used to detect this virus. However, confirmation of the infection can only be inferred by a fourfold or greater rise in virus-specific neutralizing antibody titers in either cerebrospinal fluid (CSF) or serum by performing the plaque reduction neutralization assay (PRNT) with several flaviviruses. Virus culture from CSF or serum has generally been unsuccessful due to the low level and short-lived viremia. PCR detection of this virus, thus, represents a rapid, specific and sensitive approach to detection of this virus.

Utilities:

• Confirm the disease causing agent
• Ensure that animal colonies are free of SLE virus
• Early prevention of spread of the virus among animal populations
• Minimize personnel exposure to the virus
• Safety monitoring of biological products and vaccines that derive from animals

References:
Monath, T.P. and Heinz, F.X. (1996) Flaviviruses, p. 978-984. In B.N. Fields (ed.), Fields virology, vol. 1, 3rd ed. Lippincott-Raven Publishers, Philadelphia, Pa.
Murphy, F.A., Fauquet, C.M., Bishop, D.H.L., Ghabrial, S.A., Jarvis, A.W., Martelli, G.P., Mayo, M.A. and Summers, M.D. (1995) Virus taxonomy, classification and nomenclature of viruses. Arch. Virol. 10 (Suppl): 1-586.

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