Specimen Required

Blood

Container/Tube: Serum separator (SST) or Plain Red-top tube(s)

Specimen Volume: 5 mL of whole blood

Specimen Minimum Volume: 2 mL serum

Cerebrospinal Fluid (CSF)

Container/Tube: Sterile screw cap container

Specimen Volume: 2 mL

Specimen Minimum Volume: 2 mL CSF

Transport Temperature

*The samples should be stored for not more than 2 days at 2-8^°C.

**For longer delay, freeze at -20^°C or below and transport on dry ice.

Reject Due To

Useful For

Aiding the diagnosis of arboviral (California [LaCrosse], St. Louis, Eastern equine, and Western equine virus) encephalitis

Clinical Information

Arboviruses, or arthropod-borne viruses, affecting humans are RNA viruses that are biologically transmitted to vertebrate hosts by the bite of arthropod vectors. There are more than 500 arboviruses which are grouped in at least seven families; Togaviridae, Flaviviridae, Bunyaviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, and Asfarviridae.

About 100 arboviruses cause illness in humans and through investigation of travel history and exposures laboratory and clinical diagnosis can be simplified. The majority of arboviruses result in simple febrile illness that is not uncommon to symptoms of common viral or bacterial infections. Typically clinical features of “acute arboviral fevers usually include a sudden onset of debilitating symptoms, such as malaise, extreme headache, myalgia, lumbar pain, and sometimes nausea, vomiting, and dizziness” (Lanciotti & Tsai, 2007, p. 1486). Given the large number of arboviruses there is a broad range of symptoms that may also occur including aseptic meningitis, encephalitis, flaccid paralysis, rashes, coma, and hepatitis, to name a few. Arboviruses, after penetrating the blood-brain barrier, can result in central nervous system and neuron infection and death.

Supportive care is available but there is currently no specific care for arbovirus infections. A prompt laboratory diagnosis is important in order to confirm any other potentially treatable conditions, to avoid any unnecessary treatment, and to assist public health officials in surveillance and control efforts.

Reference Values

CALIFORNIA VIRUS (La CROSSE) ENCEPHALITIS ANTIBODY

IgG:  <1:10

IgM:  <1:10

Reference values apply to all ages.

EASTERN EQUINE ENCEPHALITIS ANTIBODY

IgG:  <1:10

IgM:  <1:10

Reference values apply to all ages.

ST. LOUIS ENCEPHALITIS ANTIBODY

IgG:  <1:10

IgM:  <1:10

Reference values apply to all ages.

WESTERN EQUINE ENCEPHALITIS

IgG:  <1:10

IgM:  <1:10

Reference values apply to all ages.

Interpretation

Antibodies directed towards members of the JE serocomplex viruses (Dengue, Saint Louis Encephalitis, West Nile Virus, etc.) can cross react significantly in some serological assays. The PRNT is a more specific assay and is employed on initially reactive screening and is used to document the presence of serum antibodies specific for a particular flavivirus. Detection of organism-specific antibodies in the cerebrospinal fluid (CSF) may suggest central nervous system infection. However, these results are unable to distinguish between intrathecal antibodies and serum antibodies introduced into the CSF at the time of lumbar puncture or from a breakdown in the blood-brain barrier. The results should be interpreted with other laboratory and clinical data prior to a diagnosis of central nervous system infection.

Cautions

All results must be correlated with clinical history and other data available to the attending physician.

False-positive results may be caused by breakdown of the blood-brain barrier, or by the introduction of blood into the cerebrospinal fluid at collection.

Since cross-reactivity with dengue fever virus does occur with St. Louis encephalitis antigens, and, therefore, cannot be differentiated further, the specific virus responsible for positive results may be deduced by the travel history of the patient, along with available medical and epidemiological data, unless the
virus can be isolated.

Eastern equine encephalitis and Western equine encephalitis viruses show some cross-reactivity; however, antibody response to the infecting virus is typically at least 8-fold higher.

Clinical Reference

Beckham, J. D., and Tyler, K. L. 2010. Encephalitis, p. 1243-1263. In Mandell, D., Bennett, J. E., and Dolin, R. 2010. Principles and practice of infectious diseases, 7^th ed., vol. 1. Churchill Livingstone, Elsevier, Philadelphia, PA.

Lanciotti, R.S. and Tsai, T.F. 2007. Arboviruses, p. 1486-1500. In Murray, P. R., Baron, E. J., Jorgensen, J. H., Landry, M. L., and Pfaller, M. A. Manual of Clinical Microbiology, 9^th ed., vol. 2. ASM Press, American Society for Microbiology, Washington, DC.

Method Description

Initial screening is performed employing an enzyme-linked immunosorbent assay (ELISA). Reactive specimens are subsequently confirmed using plaque reduction neutraliation test (PRNT): Serum samples are incubated with virus and if viral neutralizing antibodies are present, they will bind to the SLE virus and prevent viral infection of cultural cells, and hence a reduction in the number of plaques detected. The neutralizing titre of a sample is expressed as the reciprocal of the serum dilution at which there is a 90% reduction in the number of plaques detected. If the patient has experienced more than one flavivirus infection, cross reactive results may yield uninterpretable results with this assay.

Performing Laboratory Location

National Microbiology Laboratory, Winnipeg, MB.