Combined detection of anti-Zika virus IgAM in acute infections
A new ELISA provides parallel detection of anti-Zika virus antibodies of classes IgA and IgM against the highly specific viral non-structural protein (NS-1). Anti-Zika virus NS-1 antibodies of class IgA are a novel alternative indicator of acute infection, and their detection is particularly useful in cases where IgM is not detectable. This can occur, for example, in patients who have had previous contact with a flavivirus through infection or vaccination (e.g. dengue, yellow fever, tick-borne encephalitis, Japanese encephalitis or West Nile viruses). When these individuals become infected with another virus of the genus Flavivirus, in this case Zika virus, the specific IgM response may be absent (secondary immune response). In these cases, determination of specific IgA can facilitate diagnosis of the acute Zika virus infection.
Studies have shown that although not all patients with an acute Zika virus infection exhibit specific IgM and specific IgA antibodies, all tested samples were reactive for at least one of the two parameters. Therefore, combined testing for IgM and IgA is beneficial for reliable diagnosis of acute infections.
In the study, serum samples of 31 patients with confirmed acute Zika virus infections from the Dominican Republic, where Zika and dengue viruses are endemic, and 40 patients from Vietnam with acute dengue virus infection were tested with the new ELISA. The Anti-Zika Virus IgAM yielded a sensitivity of 100% (31/31) and a specificity of 95% (38/40). In comparison, the Anti-Zika Virus IgM demonstrated a sensitivity of 29% (9/31) and a specificity of 100% (40/40). Thus, combined detection of both antibody classes instead of just IgM leads to a threefold increase in the sensitivity for acute Zika virus infections without a significant loss of specificity.
Early diagnosis of acute infections with Zika viruses is particularly important for pregnant women since the virus may interfere with the neurological development of the fetus and can cause microcephaly. However, also in adults the viral infection may have long-term neurological consequences. Therefore, timely recognition of this infectious disease is required.