Zika Virus IgM Persists 25 Months After Symptom Onset

Zika virus disease is caused by a virus transmitted primarily by Aedes mosquitoes, which bite during the day. Symptoms are generally mild and include fever, rash, conjunctivitis, muscle and joint pain, malaise or headache. Symptoms typically last for 2–7 days.

Zika virus infection during pregnancy is a cause of microcephaly and other congenital abnormalities in the developing fetus and newborn. Zika infection in pregnancy also results in pregnancy complications such as fetal loss, stillbirth, and preterm birth.


Scientists working with the Florida Department of Health (Tallahassee, FL, USA) assessed immunoglobulin M (IgM) detection in Zika patients from the 2016 outbreak in Miami-Dade County, Florida, USA. Demographics and clinical characteristics of the 30/62 participants in an original study who provided an additional follow-up specimen, the median age at symptom onset was 45 (range 22–70) years; all were adults >18 years of age. Fifteen (50%) were female, and 14 (47%) were Hispanic. The team found that 13 (43%) of these participants reported no international travel (outside of the continental United States) during the two years before collection of the last specimen.

The scientists tested all serum specimens at the Centers for Disease Control and Prevention (Fort Collins, CO, USA) by the IgM capture enzyme-linked immunosorbent assay (ELISA) for Zika virus. Diagnosis of Zika virus infection is accomplished by testing for viral RNA or IgM and neutralizing antibodies. Of the 30 participants who provided a follow-up specimen, 19 (63%) were positive for Zika virus IgM, 7 (23%) had an equivocal result, and four (13%) were IgM seronegative. Compared with results from the specimen collection six months earlier, 20 (67%) remained positive for Zika virus IgM, two (7%) remained Zika virus IgM equivocal, four (13%) transitioned from Zika virus IgM positive to equivocal, and four (13%) transitioned from Zika virus IgM equivocal to negative; no participants switched from Zika virus IgM positive to negative.

The authors concluded that their findings suggest that approximately three quarters of persons with polymerase chain reaction (PCR)-confirmed symptomatic Zika disease still have detectable IgM at 25 months after initial illness onset. The prolonged detection of IgM after Zika virus infection is consistent with previous findings for related flaviviruses. IgM persistence needs to be assessed with other serologic assays for both symptomatic and asymptomatic Zika virus cases to determine the full duration of Zika virus IgM after infection. The study was published on November 18, in the journal Emerging Infectious Diseases.

Related Links:
Florida Department of Health
Centers for Disease Control and Prevention