Overview: Diagnosis and Testing (continued)

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Overview: Diagnosis and Testing (continued)

Various laboratory tests are available to identify the Zika virus. Although clinical symptoms and an individual's travel and exposure history may provide clues as to a possible Zika virus infection, the most accurate means to diagnose a possible Zika virus infection is by using laboratory tests to identify the virus in the individual. Currently, there are three types of laboratory tests for the identification of the Zika virus:
  1. Nucleic Acid Tests, termed NAT by the CDC, is a generic term referring to all molecular tests used to detect viral genomic material. The most common type of NAT used for Zika virus testing is Real-time reverse transcription-polymerase chain reaction (rRT-PCR) for measuring Zika virus RNA in serum and urine.
  2. The Zika IgM antibody capture enzyme-linked immunosorbent assay (Zika MAC-ELISA) for detecting Zika virus IgM antibodies in serum.
  3. Plaque reduction neutralization test (PRNT) to confirm the presence of Zika virus-specific antibodies.
Note: More information on the three types of Zika virus tests will be presented in other sections of this course.
During the course of the disease, Zika virus-specific IgM and neutralizing antibodies typically develop toward the end of the first week of illness. Moreover, the IgM levels can vary, but usually, IgM levels are positive beginning near day four after the presentation of symptoms and the presence of IgM antibodies will continue for about 12 weeks.
Nucleic acid testing (NAT), namely rRT-PCR, measures the Zika virus RNA and is generally employed early in the course of the infection. It should be performed on serum collected during the first two weeks after symptoms occur, In addition, rRT-PCR or NAT should be performed on urine samples matched to patient serum specimens collected less than 14 days after symptom onset. Typically, a positive rRT-PCR or NAT result on any specimen will confirm a Zika virus infection, and usually, no additional testing is required. However, a negative rRT-PCR or NAT result does not exclude the Zika virus infection; therefore, the serum should then be analyzed by a serological test for the Zika virus IgM antibody.
Note: More information on recommended testing for the Zika virus will be presented in the section dealing with the CDC guidelines on Zika testing and diagnosis.