Reverse transcriptase-polymerase chain reaction (RT-PCR) for Zika virus diagnostic test

- Background

Zika, chikungunya, and dengue virus are from the same family, Flavivieidae, and genus, Flavivirus. Regarding to the Zika virus outbreak in South American countries since 2015 and increasing confirmed cases in south-east Asia countries, patients with acute fever, rash, myalgia, or arthralgia and have traveled within the previous 2 weeks to above areas which with ongoing Zika virus transmission should all be considered a Zika virus infection1.

Laboratory evidence of Zika virus infection is generally accomplished by testing serum to detect viral nucleic acid or virus specific immunoglobulin (Ig) M and neutralizing antibodies. However, serological cross reactivity may occur between Zika and other flaviviruses (e.g., dengue, yellow fever, St. Louis encephalitis, Japanese encephalitis, West Nile), so emphasis should be placed on molecular testing with reverse transcriptase-polymerase chain reaction (RT-PCR) in acute specimens received from individuals with clinically compatible illness1
.


- High specificity RT-RCR test

Due to serological cross-reactivity between Zika virus and other flaviviruses, current IgM antibody assays cannot reliably distinguish between Zika and dengue virus infections, which is also popular in Hong Kong. The RT-PCR assay kit in our laboratory detects the presence of Zika virus specific RNA molecules in clinical specimens, which offers 100% specificity and does not cross react with non-Zika flaviviruses and more than 50 frequently seen pathogens. Meanwhile, it is validated with CE-IVD mark and the detection limit is as low as 10 copies per micro-liter. (validation report provided by the assay kit manufacturer)


-Test Characteristics

Zika virus was detected in whole blood (both serum and plasma), urine, cerebrospinal fluid, amniotic fluid, semen and saliva2. Recent study showed that Zika virus could be detected in urine sample by RT-PCR up to 15 days after symptom onset; whereas it was detected for 7 days in serum samples3. Taken together, WHO suggested that nucleic acid detection by RT-PCR targeting Zika virus specific genomic region is the primary means of diagnosis4. Preferred clinical specimens are serum or plasma collected within first 3 days of symptoms onset or urine samples after that.


References

1. Revised diagnostic testing for Zika, chikungunya, and dengue viruses in US Public Health Laboratories. Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, the U.S. Department of Health and Human Services. (https://stacks.cdc.gov/view/cdc/38149)

2. Laboratory testing for Zika virus infection. The World Health Organization. (http://www.who.int/csr/resources/publications/zika/laboratory-testing/en/)

3. Gourinat AC, O'Connor O, Calvez E, Goarant C, Dupont-Rouzeyrol M. Emerg Infect Dis. 2015 Jan;21(1):84-6. doi: 10.3201/eid2101.140894.

4. Zika Virus fact sheet. The World Health Organization. (http://www.wpro.who.int/mediacentre/factsheets/fs_05182015_zika/en/)