Laboratory Diagnosis of Zika Virus: What You Need to Know

The Zika virus is transmitted by mosquito and the first US case has just been confirmed in Texas, USMicrocephaly Microcephaly is a term that encompasses a number of different disorders, in which a baby is born with a head smaller than usual. This also often means that a baby’s brain is also smaller and has not developed properly. The World Health Organisation (WHO) says a causal link between Zika virus and brain defects is strongly suspected.

The Zika virus is a mosquito borne virus that was first isolated in the Zika Forest of Uganda in 1947. The virus is currently spreading through more than 20 countries in the Americas including Brazil, Bolivia, Venezuela and Mexico.

Symptoms of Zika virus infection

The Zika virus causes a relatively mild infectious disease, symptoms include fever, headache, joint pain, rash and conjunctivitis. Although the Zika virus is capable of causing serious complications and deaths in adults, the greatest concern regarding this infection is that it appears to cause congenital abnormalities, Guillain-Barré syndrome and other neurological defects in unborn babies. In particular, Zika virus infection causes microcephaly, in which children are born with unusually small heads. In a small number of cases, children born with microcephaly may be able to lead an almost normal life, however the severity of this disorder can range significantly and many children are severely disabled and unable to lead a normal life.

Lab testing is essential for the accurate diagnosis of Zika virus. There are no clinically approved, commercially available tests for the diagnosis of Zika virus infection. Testing is performed in highly specialized laboratories using laboratory developed tests. Zika virus antigens, such as those produced by Aalto Bio Reagents, are being developed in the hope that a commercially viable diagnostic platform will soon be available.

Although evidence of infection can be determined in serum via the detection of viral nucleic acid or virus-specific IgM and related antibodies, there is strong serological cross-reactivity between Zika and dengue viruses. For this reason, the molecular testing of acute specimens is necessary¹. During the initial acute phase of infection (the first week), Zika virus can be diagnosed using reverse transcriptase-polymerase chain reaction (RT-PCR) in serum.

Zika virus can be diagnosed using reverse transcriptase-polymerase chain reaction (RT-PCR) in serum

Once the acute phase testing window has closed, it is possible to detect Zika IgM in an ELISA test for several months after the onset of infection. However, due to the cross-reactivity between Zika and the dengue viruses, a positive result can only be indicative of a recent flavirus infection.

Laboratory testing in the UK

For suspected Zika cases in the UK, the Governmental advice is to ‘send the appropriate samples (with a full clinical and travel history) to Public Health England’s Rare and Imported Pathogens Laboratory (RIPL)'². You can find further information in the Rare and Imported Pathogens Laboratory Specimen: Referral Guidelines and Service User Manual.

Laboratory testing n the US

For suspected Zika cases in the US, samples can be sent to the Centre for Disease Control (CDC). The CDC provides instructions for sending diagnostics specimens to CDC which include detailed instructions for completing the CDC specimen submission form 50.34.

References:

1. http://www.cdc.gov/zika/pdfs/denvchikvzikv-testing-algorithm.pdf

2. https://www.gov.uk/guidance/zika-virus#epidemiology