Mayo Clinic will offer the Zika virus antibody test developed by the Centers for Disease Control and Prevention (CDC).This test has received Emergency Use Authorization (EUA) from the U.S. Food and Drug Administration (FDA) and has been licensed to select national reference laboratories, including Mayo Medical Laboratories (MML).
The CDC's test, the Zika Immunoglobulin M (IgM) Antibody Capture Enzyme-Linked Immunosorbent Assay (a.k.a., Zika MAC-ELISA), is intended to be used as a screen for Zika virus infection in individuals meeting clinical and/or epidemiological criteria established by the CDC. Mayo Clinic will follow the CDC's recommended guidelines for Zika virus testing, enabling U.S. health care providers to send testing directly to Mayo Medical Laboratories. For existing MML clients, the Zika MAC-ELISA will only be offered in the United States and U.S. territories.
Faster Turnaround Time for Zika Test Result
"An individual can now receive his or her screening result for Zika virus within 48 hours compared to having to wait a week — or longer — for that same result to come back from the CDC or a public health laboratory," says Elitza Theel, Ph.D., a clinical microbiologist and director of the Mayo Clinic Infectious Diseases Serology Laboratory. "For someone worried about potentially being infected with Zika virus, this is a significantly faster turnaround time."
Dr. Theel is quick to add that positive results from the Zika MAC-ELISA still require confirmatory testing by the CDC's plaque reduction neutralization test. She says, "Confirmation from the CDC is necessary because the Zika MAC-ELISA may produce false positive results in patients previously or concurrently infected with dengue virus."
Dengue virus is closely related to, and transmitted by, the same mosquitoes that carry Zika virus. Dr. Theel says, "Providers caring for pregnant women who test positive for antibodies to Zika virus by this screening test may begin to monitor the pregnancy more closely and sooner while they wait for confirmatory testing to return from the CDC."
Test Methodologies Available Today
Two main methodologies for detecting Zika virus exist today:
A polymerase chain reaction (PCR) assay for detecting viral RNA
Serologic tests to detect antibodies to Zika virus
The duration of a patient's symptoms, exposure history and the specimen source should determine which methodology is most appropriate.
"Currently, the CDC recommends that PCR be performed on serum and urine collected within the first two weeks after symptom onset or possible exposure to Zika virus," says Dr. Theel. "While a positive PCR result confirms Zika virus infection, PCR-negative patients require follow-up by a Zika antibody test, such as the Zika MAC-ELISA."
The Zika MAC-ELISA is also recommended as the first-line test to evaluate patients who are more than 14 days post-symptom onset and individuals whose last possible exposure to Zika virus was more than 14 days prior.
What Health Care Providers Need to Know
According to the CDC, the most common symptoms of Zika virus infection are fever, rash, joint pain and conjunctivitis (red eyes). Other common symptoms include muscle pain and headaches. However, only approximately 20 percent of infected patients develop symptoms. The time from exposure to symptom onset for Zika virus is not well-characterized but can range from two to 14 days.
"The mosquito species that transmits Zika virus also transmits both dengue and chikungunya viruses, which co‑circulate in Zika-endemic areas," says Dr. Theel. "It's therefore important for health care providers to also consider infection from these viruses, as symptoms often overlap." For this reason, Mayo Clinic is offering a Zika MAC-ELISA and dengue virus IgM panel for pregnant women and non-pregnant individuals meeting clinical criteria.
The CDC's Zika MAC-ELISA test has not been cleared or approved by the FDA. The test has been granted EUA by the FDA and has been licensed to select laboratories — such as Mayo Medical Laboratories — by the CDC for use while circumstances exist to justify the EUA. Also, the Zika test is authorized only for the detection of Zika virus infection and not any other viruses or pathogens. As required by the FDA, Mayo Clinic will report all presumptive positive, equivocal, and inconclusive results by this test to the CDC and other public health authorities, as appropriate.
More Information about Zika
Zika virus is known to circulate in Africa, the Americas, Asia, and the Pacific through Aedes species mosquitos: primarily, Aedes aegypti and Aedes albopictus. In the U.S., these mosquitoes are found mainly in the Gulf Coast and Atlantic Coast states, though, they also are expanding inland into the Midwest. As recently reported in a New York Times article, there have been 42 reported cases in Florida of Zika virus infections that were acquired locally, making this disease a growing public health threat in the U.S.
"In spite of increased environmental controls such as spraying for mosquitoes, cases of locally acquired Zika virus will likely continue to increase in Florida," says D. Jane Hata, Ph.D., director of the Clinical Microbiology and Serology Laboratories at Mayo Clinic in Florida. "The availability of a serologic assay with a more rapid turnaround time will aid clinical management in appropriately tested patients and reduce the current burden on public health laboratories performing Zika testing."
Dr. Hata adds, "We also cannot afford to forget about the possibility of dengue fever, which is another advantage to the panel approach of offering the Zika MAC-ELISA alongside a dengue IgM test."
There is currently no vaccine against Zika virus. Once diagnosed, most people recover fully, with symptoms resolving in about one week.
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