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CDC Recommends Zika Testing for Some Pregnant Women; Labs Developing New MDx Assays

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NEW YORK (GenomeWeb) – Pregnant women who have traveled to any of about 25 countries with ongoing Zika virus transmission and who report two or more symptoms — including acute-onset fever, rash, joint pain, and conjunctivitis — should be evaluated for infection, the US Centers for Disease Control said this week.

Its interim guidelines came in response to an ongoing outbreak and correlations between prior infection with the arbovirus and birth defects. The CDC also issued guidelines for testing newborns who may have been infected in utero.

Today, Altona Diagnostics launched a CE-IVD marked real-time PCR test for Zika, making it the first commercially available molecular test. Meanwhile, others are developing assays, and the CDC test is being adopted by state and local health labs.

The CDC recommends acute testing for Zika be performed using molecular assays, and convalescent samples be evaluated with immunoassays. However, due to "extensive cross-reactivity in flavivirus serological assays," molecular detection should be performed first for samples collected less than seven days after illness onset. For infants with exposed mothers, or ones who are born with microcephaly, RT-PCR testing should be performed on serum specimens collected from the umbilical cord or directly from the infant within two days of birth, the CDC said.

Although the virus was first isolated from an infected monkey in the Zika forest of Uganda in 1947, transmission among humans was rare until a 2007 outbreak on the Yap Islands in Micronesia. The PCR assay used by the CDC was developed to assess the Yap outbreak, and was published in 2008 in Emerging Infectious Diseases. It works on serum, but was also described to work on urine in a recent study.

"It's a very standard qRT-PCR assay following very standard methods and approaches," Ann Powers, chief of the Alphavirus Laboratory at the Division of Vector-Borne Diseases in the National Center for Emerging and Zoonotic Infectious Diseases, told GenomeWeb in an interview. 

According to a memorandum published earlier this month, the test follows essentially the same protocol as the CDC's West Nile virus RT-PCR assay. "Basically you just swap out different primers and probes, the positive control is different, but the method itself is actually virtually identical," Powers said.

State health department labs that run the West Nile assay, or that have passed a proficiency panel in the past, would be qualified to perform the Zika test on whatever PCR platform they use, Powers said.

Test volumes

During the EV-D68 outbreak in 2014, the CDC's polio and picornavirus laboratory ultimately accommodated a spike in test volume by updating the PCR-based assay for that virus.

However, so far the Arbovirus Diagnostic Laboratory is not getting a huge volume of samples, Powers said.

"We're probably getting fewer than 100 per week for testing — that's our total sample volume and could include requests for different testing as well," she said, estimating that probably somewhere around 80 percent of those requests right now relate to Zika.

This volume is about 25 percent of the capacity for the lab, Powers said, so it could scale up significantly if needed. State labs will also soon be able to absorb additional test requests, and Powers said, "A number of our partners and some of the CDC facilities have high-throughput testing capacity, they can do 300 samples at a time, basically, so I think the capacity is in very good shape for the molecular assay."

Other tests

Besides the CDC RT-qPCR, there is at least one additional published assay. A group based in Senegal purports that its test can detect a wider genetic diversity, and used it to detect Zika in field-caught mosquitoes.

At Stanford University, Jesse Waggoner and Benjamin Pinsky have developed a single-reaction, multiplex, real-time RT-PCR assay for Zika, chikungunya, and dengue viruses. The test is currently being implemented by collaborating institutions in several countries in Central and South America, Pinsky said in an email.

"Given the co-circulation of these mosquito-borne pathogens and their similar clinical presentations, tests such as this one should be useful for clinical decision-making and ongoing epidemiologic surveillance," he added.

The Stanford group is interested in collaborations to develop the assay further. "Our goal is to make this test as widely available as possible," Pinsky said, adding that could be "through industry partners or not-for-profit funding opportunities that will allow us to distribute our test free of charge to requesting laboratories." Pinsky's lab has also developed a test for differential diagnosis of dengue, leptospirosis, and malaria, as previously reported.

Meanwhile, at least one commercial firm has pursued regulatory approval for a Zika test. Hamburg, Germany-based Altona Diagnostics officially launched a CE-IVD real-time PCR test for Zika today. The RealStar Zika Virus RT-PCR kit adds to a growing number of CE-IVD marked, ready-to-use kits from the firm for detection of tropical pathogens. In suspected Zika infections, chikungunya and dengue infection must also be ruled out, and Altona also offers kits for those viruses, the firm noted in a statement.

Ruling out dengue serologically using immunoassays can be tricky. Zika virus is "very closely related to other related flaviviruses antigenically", and "the assay tends to be somewhat cross-reactive," Powers noted. On the other hand, patients are only viremic for about one week, so Powers suggested that ultimately immunoassays that are more specific for Zika would be very useful to the field.

One other firm, Quest Diagnostics' Focus Diagnostics business, may be developing a Zika test, but whether it will be PCR- or immunoassay-based is unknown.

Focus "has a record of being the first commercial provider to offer patients and physicians clinical tests for emerging infectious diseases, such as chikungunya and the H1N1 flu virus," Wendy Bost, Quest's director of corporate communications told GenomeWeb in an email.

"We are following the current Zika outbreak closely, which is not currently impacting the US, and exploring a development pathway for a test with potential to enhance patient management," Bost said.

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