APHL rang in the New Year by responding to another emerging infectious disease: Zika.

Aedes aegypti mosquito

by Kelly Wroblewski, MPH, MT(ASCP), director, Infectious Diseases

Appearing in South America in 2015, the virus spread northward with the first case reported in Puerto Rico on December 31. As the entire public health system began to mobilize, APHL held the first Zika-focused All-Member Laboratory Alert call on January 28, 2016, and public health laboratories (PHLs) began implementing new tests to detect evidence of Zika infection.

A vector-borne flavivirus spread primarily by the Aedes aegypti mosquito, Zika presents an unusual challenge for public health professionals. While many infectious diseases have limited long-term effects once a patient recovers, women who contract Zika during pregnancy appear to face a higher risk of having infants with a wide range of birth defects, including a condition called microcephaly.

Two types of assays are available to detect evidence of Zika infection: a Reverse Transcription-Polymerase Chain Reaction (RT-PCR) test, and the IgM Enzyme Linked Immunosorbent Assay (IgM ELISA). RT-PCR is a molecular assay that detects viral RNA of Zika in serum, urine or amniotic fluid. The assay is very sensitive and specific for Zika, but only if the patient being tested is symptomatic and the specimen was collected within seven days of symptom onset. When patients are not actively sick but want to learn if they were exposed to the virus, particularly in the case of pregnant women, laboratories use IgM ELISA, a serology assay that looks for antibodies to the virus in serum. While this test provides a longer window for testing, the test is not very specific for Zika.

Because Zika is closely related to other flaviviruses, namely dengue, it is very difficult to distinguish the Zika antibodies that infected people develop from other flavivirus antibodies that may have developed following exposure to other viruses, something known as cross-reactivity. To resolve potential cross-reactivity, any positive IgM ELISA specimen needs to be resolved with a more complex serologic test called the Plaque Reduction Neutralization Test (PRNT). While PRNT will usually distinguish between the closely related viruses, it takes a minimum of seven days to perform and requires very specialized skills. Because of these factors, there is an increase in testing turnaround times and a limited number of laboratories that provide the test.

Despite these challenges, APHL and PHLs continue to do what they can to provide access to the best tests available, as well as respond to emerging questions and issues. On April 1, more than 300 public health professionals and government officials gathered in Atlanta for the Zika Action Plan Summit (ZAP). ZAP provided an opportunity for state and local jurisdictions to compare active Zika response plans, as well as refine them using direct access to subject matter experts from federal agencies.

“This is [going to] take a whole community response, with partners that we might not traditionally work with,” acknowledged Dr. Nicole Lurie, assistant secretary for preparedness and response, Department of Health and Human Services. “But [everyone] need[s] to be at the table.” Therefore, the usual public health partners of epidemiology, laboratory and preparedness staff are partnering with vector control, maternal and child health and environmental health professionals in an unprecedented exchange of data and information.

At press time, 37 public health laboratories have implemented testing for Zika virus. APHL has convened a Zika Technical Working Group, facilitated frequent member calls and released a Risk Assessment Template and Frequently Asked Questions document. As this challenging response continues to evolve, public health laboratories and APHL will continue to detect and respond.