Emergency Zika Test Approved by FDA

Updated Sunday, March 20: The CDC said Friday it had approved the emergency use of a new test for the Zika virus. The test, called a Trioplex Real-time RT-PCR Assay, represents a diagnostic breakthrough in that it will also detect infections by chikungunya and dengue. Previously, those viruses could only be identified with separate tests.

The new test was approved at the request of the CDC. It "will potentially allow CDC to more rapidly perform testing to detect acute Zika virus infection," the CDC said.

The test, which was developed by the CDC's Dengue Branch in San Juan, Puerto Rico, will be distributed to "qualified laboratories" in the Laboratory Response Network, created in 1999 to respond to bioterrorism but which has since branched out to tackle other health emergencies. The test will not be available in U.S. hospitals or other primary care settings, the CDC said.

Dr. Michael P. Busch, director of the Blood Systems Research Institute and a professor of laboratory medicine at the University of California, San Francisco, is familiar with the new CDC test. He said the test will only detect the virus for a period of 1-2 weeks, when it's actively replicating and those infected are showing symptoms.

"If you're a pregnant woman and coming back from Brazil," he said, the virus may be long gone from your body. It could have affected your fetus, but [your] blood is no longer positive for the virus."

He said more-sensitive tests are now in development, and that these would be able to detect the virus in those who are asymptomatic -- the majority of cases.

The FDA had previously given emergency approval to a different test, called Zika MAC-ELISA, on Feb. 26. That test has been seen as the best available till now, according to NPR. The test has one noteworthy drawback, however: It finds false positives.

Busch said PCR assays like the one from the CDC are much less prone to false positives.

Meanwhile, Dr. Charles Chiu, also from UCSF, says he plans to deploy a portable test, using a technology called nanopore sequencing. at laboratories in areas most affected by the virus. Chiu says his test can detect any viral, bacterial, fungal, or parasitic agent. He told KQED's Lesley McClurg a couple of weeks ago that a clinical microbiologist from Barbados was being trained in the technique.

Current State of the Outbreak

The Zika virus has been linked to a neurological condition called microcephaly, in which the head of an infant is significantly smaller than normal. Brazil has been especially hard hit. Its health ministry said today the number of microcephaly cases now stands at 5,131.

The Associated Press reported today that a lack of insecticide in the country, to kill the mosquitoes that transmit the virus, is just one of the factors contributing to its spread there.

The virus has been detected mostly in South America, Central America, Mexico and the Caribbean. In the U.S., 258 cases have been reported, all associated with travel outside the country. Thirty-five of those infected are pregnant. There has yet to be a case in the U.S. of local transmission through mosquitoes. But transmission through sexual contact has occurred.

The CDC today issued interim recommendations for "Zika vector control" --  the eradication of the two mosquito types that carry the virus.

Despite what many Americans think, the disease that results from the virus is not fatal. It has, however, been known to trigger Guillain-Barré syndrome, an autoimmune disease.