Detection of Zika virus RNA or IgM antibody in serum samples are the mainstay of diagnosis.
Blood, serum, urine, semen, amniotic fluid and tissue specimens are the main samples for Zika virus diagnosis.
Detection of Zika virus RNA: Zika virus RNA can be detected within the first week of illness by molecular tests such as reverse transcriptase PCR or real-time PCR. Virus RNA becomes negative towards the end of first week as the antibody starts appearing. Commercially available Zika virus PCR system is available.
Detection of IgM antibody: Diagnosis from single serum sample can be done by detection of specific IgM antibody during the second week of illness by using capture ELISA (MAC ELISA). Zika virus IgM MAC ELISA is commercially available.
Antigen detection: Virus antigen detection by immunohistochemistry using monoclonal antibody can be done in tissues.
Isolation of virus: Zika virus isolation can be done by mice inoculation or by cell culture using monkey kidney cell lines (Vero, LLCMK2) or mosquito cell lines (C6/36). However, the method is not often used for patient diagnosis.
Approach to diagnosis: Zika virus testing should be done in the following clinical settings:
• Occurrence of cluster of cases with dengue like illness.
• Individuals returning from countries where Zika virus transmission is going on.
Zika virus RNA detection by reverse transcriptase polymerase chain reaction (RT PCR) is preferred during the first week of illness and IgM detection by MAC ELISA during the second week of illness or when RT-PCR is negative. In case of IgM positivity, the sample should ideally be subjected for plaque reduction neutralization test (PRNT) in order to rule out the cross-reactivity with other flaviviruses.
