Dengue

Test code: S0060 - Ultrasensitive qualitative detection of Dengue virus by reverse transcription real time polymerase chain reaction

Dengue viruses belong to the family Flaviviridae which contains close to 70 different viruses. These include viruses causing yellow fever and several encephalitides, such as Japanese encephalitis and tick-borne encephalitis. There are four distinct serotypes of Dengue virus that are all mosquito-borne (Gubler, 1998; Halstead, 1997). Each of the four Dengue virus serotypes can produce a wide spectrum of disease severity. The Dengue fever (DF) is the most common, and occurs more frequently among older children and adults. DF is self-limiting and is characterized by a sudden onset of nonspecific indicators such as headache, myalgia, arthralgia and rashes. DF can range in severity from a minor infirmity to a temporarily incapacitating syndrome with residual fatigue and depression.

At the extreme of Dengue virus infection is the Dengue hemorrhagic fever (DHF), which primarily affects children under the age of 10 years. The clinical symptoms of DHF include plasma leakage, a bleeding tendency, and liver involvement, which may lead to potentially life-threatening syndromes including disseminated intravascular coagulation and Dengue shock syndrome. There are no vaccines for Dengue, and treatment is limited to supportive therapies. It is estimated that 50-100 million people suffer from Dengue fever annually and hundreds of thousands of cases of Dengue hemorrhagic fever occur in the tropics every year (Gubler, 1998; Halstead, 1997).

Primates such as chimpanzees can be experimentally infected by Dengue viruses followed by viremia but they do not show clinical symptoms (Scherer et al., 1978). They become carriers and facilitate transmission of the virus. Serological studies have shown widespread exposure of wild monkeys to this virus (Furumizo and Rudnick, 1979; Wolfe et al., 2001). Thus, laboratory personnel involved in handling monkeys are highly susceptible to infection by this virus.

The virus contains a positive RNA genomic strand approximately 11 kb in length. Studies of evolutionary relationships between the four serologically distinct Dengue viruses have shown that each serotype can further be subdivided into several major genotypes or monophyletic groups. For example, five genotypes or monophyletic groups have been described for Dengue 1 virus.

Dengue virus infections can be confirmed by serological testing or virus isolation by culture in insect cells or mosquito inoculation, but these methods are time consuming, labor intensive and have limited sensitivity for detecting low levels of the virus. For serological determination of Dengue viral infection, a definitive diagnosis requires testing of acute- and convalescent-phase samples, usually collected at least 7 days apart, to demonstrate a fourfold or greater increase in antibody titer. This time lapse delays the assignment of the correct treatment regimen. PCR detection of Dengue virus is not only quick (usually less than 2 days) but is also sensitive and specific.

Utilities:

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

References:
Furumizo, R.T. and Rudnick, A. (1979) Laboratory observations on the life history of two species of the Aedes (Finlaya) niveus subgroup (Diptera: Culicidae) in Malaysia. J Med Entomol 15: 573-575.
Gubler, D.J. (1998) Dengue and dengue hemorrhagic fever. Clin. Microbiol. Rev. 11: 480-496.
Halstead, S.B. (1997) Epidemiology of dengue and dengue hemorrhagic fever, p. 23-44. In D. J. Gubler and G. Kuno (ed.) Dengue and dengue hemorrhagic fever. CAB International, Wallingford, United Kingdom.
Scherer, W.F., Russell, P.K., Rosen, L., Casals, J. and Dickerman RW (1978)Experimental infection of chimpanzees with dengue viruses. Am J Trop Med Hyg 27: 594-599.
Wolfe, N.D., Kilbourn, A.M., Karesh, W.B., Rahman, H.A., Bosi, E.J., Cropp, B.C., Andau, M., Spielman, A. and Gubler, D.J. (2001) Sylvatic transmission of arboviruses among Bornean orangutans. Am. J. Trop. Med. Hyg. 64:310-6.

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