Venezuelan Equine Encephalitis, Eastern Equine Encephalitis and Western Equine Encephalitis

Test codes:
S0054 - Ultrasensitive qualitative detection of Venezuelan Equine Encephalitis virus by reverse transcription real time polymerase chain reaction
S0055 - Ultrasensitive qualitative detection of Eastern Equine Encephalitis virus by reverse transcription real time polymerase chain reaction
S0056 - Ultrasensitive qualitative detection of Western Equine Encephalitis virus by reverse transcription real time polymerase chain reaction
P0014 - Equine neurological panel (includes EEE, WEE and other pathogens)

Venezuelan equine encephalitis (VEE), eastern equine encephalitis (EEE) and western equine encephalitis (WEE) viruses are arthropod borne viruses (arboviruses). They are members of the family Togaviridae, genus Alphavirus. Members of the genus Alphavirus have a spherical, enveloped virion 60 to 65 nm in diameter and possess a single-stranded, positive-sense RNA genome over 11 kb in length. The natural transmission cycles of these three viruses involve a variety of mosquito and avian species. Under unique ecological conditions, VEE, EEE and WEE viruses are transmitted from avian hosts to dead-end hosts such as equines, non-human primates and humans. They are associated with both human and equine encephalitis throughout the Americas. Geographically, there is a difference in the distribution of these three antigenically and ecologically distinct viruses. The majority of EEE virus activity has occurred in the eastern United States within the geographic range of Culiseta melanura, the primary insect vector of North American EEE virus. The majority of WEE virus activity has occurred in the western United States, where Culex tarsalis is the primary mosquito vector of WEE virus . In contrast to both EEE and WEE, the distribution of VEE is primarily restricted to Central and South America.

It is also important to note that there are two major antigenic groups of EEE virus; the North American group includes isolates of EEE virus from the United States, Canada, and the Caribbean, while the South American group includes isolates of EEE virus from Central and South America. North American strains of EEE virus are considered to be more virulent than South American strains of EEE virus, which are rarely associated with human illness.

VEE consists of related, but distinctive viruses that are grouped as a complex consisting of six antigenic subtypes (I to VI). Viruses of subtypes I and III are further differentiated into five (IAB to IF) and three (IIIA to IIIC) antigenic varieties. Although VEE is mostly found in Central and South American, there are two exceptions: The Everglades virus (EVE) found in Florida (Chamberlain et al., 1964) which is antigenically classified as VEE subtype II though it is genetically more closely related to IAB and IC viruses; and the Bijou Bridge virus detected in Colorado (Monath et al., 1980), which is genetically and antigenically classified as subtype IIIB virus. VEE epizootics are mainly caused by subtype IAB and IC viruses, and they occur frequently in South America, including a 1969 to 1972 pandemic which spread from Central American to Texas. VEE has been a major health concern. In 1995, there was a large epizootic in Venezuela and Colombia that involved about 75,000 humans and 50,000 equids (Rivas et al., 1997; Weaver et al., 1996).

The clinical presentations of EEE-, WEE-, or VEE-infected humans, primates and horses are non-specific, and a panel of non-viral and non-infectious etiologies has to be considered. Although there is no treatment for infection by these viruses, a fast and specific diagnosis is needed to prevent further spread of the disease by quarantine, trade restriction, vaccination and vector control.

Virus isolation by intracerebral inoculation of baby mice or cell cultures has been the gold standard for virus detection. However, this method is time consuming. PCR detection of these viruses is now considered as the most rapid, specific and sensitive detection method.

Utilities:

• Confirm the disease causing agent
• Ensure that animal populations are free of VEE, EEE and WEE virus
• Early prevention of spread of the virus among an animal population
• Minimize personnel exposure to the virus
• Safety monitoring of biological products and vaccines that derive from horses and primates

References:
Chamberlain, R.W., Sudia, W.D., Coleman, P.H. and Work, T.H. (1964) Venezuelan equine encephalitis virus from south Florida. Science 145: 272-274.
Monath, T.P., Lazuick, J.S., Cropp, C.B., Rush, W.A., Calisher, C.H., Kinney, R.M., Trent, D.W., Kemp, G.E., Bowen, G.S. and France, D.B. (1980) Recovery of Tonate virus (“Bijou Bridge” strain), a member of the Venezuelan equine encephalomyelitis virus complex, from Cliff Swallow nest bugs (Oeciacus vicarium) and nestling birds in North America. Am. J. Trop. Med. Hyg. 29: 969-983.
Rivas, F., Diaz, L.A., Cardenas, V.M., Daza, E., Bruzon, L., Alcala, A., de la Hoz, O., Caceras, F.M., Aristizabal, G., Martinez, J.W., Revelo, D., de la Hoz, F., Boshell, J., Camacho, T., Calderon, L., Olano, V.A., Villarreal, D., Roselli, D., Alvarez, G., Ludwig, G. and Tsai, T. (1997) Epidemic Venezuelan equine encephalitis in La Guarjira, Colombia, 1995. J. Infect. Dis. 174: 828-832.
Weaver, S.C., Salas, R., Rico-Hesse, R., Ludwig, G.V., Oberste, M.S., Boshell, J. and Tesh, R.B. for the VEE Study Group (1996) Re-emergence of epidemic Venezuelan equine encephalomyelitis in South America. Lancet 348:436-440.

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