ST. LOUIS ENCEPHALITIS IGG ANTIBODY BY IFA, SERUM

Code
000.0000
Name
ST. LOUIS ENCEPHALITIS IGG ANTIBODY BY IFA, SERUM
Category
None
Department
Send-Out
Start Date
Expiration Date
Synonyms
SLE Ab
CPT Codes
86653
Site
IDPH
Reference Test
ATLAS Test Code

Specimen Information

Type

Gold, SST or CSF

Volume

Serum: 3.0 ml
CSF: 1.0 ml

Transport Info

2 weeks refrigerated

Fasting Required?
False
Patient Instructions

Reference Range

Less than 1:16 = No IgG antibody detected
Equal to or greater than 1:16 = IgG antibody detected, which may suggest current or past infection.

Methodology

Indirect Fluorescent Antibody

Clinical Significance

St. Louis encephalitis (SLE), western equine encephalitis (WEE), and California encephalitis (CE) group viruses are the major mosquito-borne viruses causing human disease in the U.S. Eastern equine encephalitis (EEE) is seen less frequently, but is also similar in its seasonal occurrence and overlaps in regional distribution. Since viral isolation attempts from these cases are seldom productive, the majority of human cases are diagnosed by serologic means. SLE is a member of the genus Flavivirus and is closely related antigenically to other members of this genus that are known to cross-react by IFA methods. SLE is the only Flavivirus of clinical significance in the continental U.S., although human infection occurs both as urban epidemics and sporadic rural cases throughout the U.S. Principle vectors are thought to be Culex nigripalpus in Florida, C. pipiens-quinquefasciatus in the eastern U.S., and C. p. quinquefasciatus and C. peus as urban vectors of SLE. The urban SLE cycle involves not only the wild, primarily passerine birds for amplification (rural cycle), but also ducks, chickens, and other domestic or urban bird species. Asymptomatic infections by these viruses are the most common. Inapparent infections by SLE outnumber clinically apparent ones by 800:1 in patients under ten years of age and 80:1 in those over 60 years. The second most common manifestation is a mild, nonspecific febrile illness, usually with headache. Central nervous system involvement by these viruses is very similar, with the exception of a more abrupt onset and shorter, more severe course found with EEE. Children generally are more often susceptible to severe disease, although SLE affects older adults more often and more severely. Initially symptoms include headache, fever, malaise, and vomiting. Convulsions are less common in SLE than in CE, WEE, and EEE. Supportive therapy and intensive nursing are required in all these cases. Fatality rates are approximately ten percent for SLE. Single positive antibody titers may indicate past or current infection. Serum specimens drawn within the first two weeks after onset are variably negative for IgG antibody and should not be used to exclude the diagnosis of arboviral disease. Seroconversion between acute and convalescent sera is considered strong evidence of recent infection. The best evidence for infection is a significant change (fourfold difference in titer) on two appropriately timed specimens, where both tests are done in the same laboratory at the same time. Antibody to any of the Flavivirus group (Group B viruses) will react quite strongly with the SLE viral antigen and, therefore, cannot be differentiated further. The specific virus responsible for such a titer must be deduced by the travel history of the patient, along with available medical and epidemiological data, unless the virus can be isolated.

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