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Zika virus disease is caused by the Zika virus, which primarily spreads to humans through the bite of an infected mosquito. It can also be spread from mother to child, though sexual contact, or through blood transfusions. On February 1, 2016, the World Health Organization (WHO) declared the Zika outbreak in South America a public health emergency.
Zika virus causes mild symptoms such as fever, rash, joint pain, conjunctivitis (red eye), muscle pain, and headache, and can last from several days up to a week. The incubation period is currently unknown, but likely to be a few days. Many people who contract Zika virus do not know that they have it, since the symptoms are similar to many other diseases, such as dengue or chikungunya. Some people do not experience any symptoms. This makes it challenging to account for all of the people who contract the disease during an outbreak. While the mortality rate from Zika virus is very low, there is a serious risk for complications – especially in the fetus of a pregnant woman who has or had Zika virus.
Zika virus can often be detected in the week after the onset of symptoms through the detection of viral RNA in serum. Reverse transcription-polymerase chain reaction (RT-PCR) is the preferred test for Zika virus. RT-PCR can detect the presence of RNA from Zika virus and differentiate it from the RNA of a similar virus, like dengue or chikungunya. A false or negative RT-PCR result can be confirmed with an IgM ELISA to test for the presence of antibodies against Zika virus. Virus-specific IgM antibodies may be detectable ≥4 days after the onset of illness – however, it can be difficult to distinguish antibodies against Zika virus from those for dengue viruses and other flaviviruses, which can result in false positives.
Zika virus may also be detected in people who no longer have symptoms. IgM antibodies against Zika can persist for two to twelve weeks after infection – although distinguishing Zika from other flaviviruses remains an issue.
There are currently no commercially available Food and Drug Administration (FDA)-cleared diagnostic assays or kits for Zika virus infection in the United States. The FDA has issued an Emergency Use Authorization for two diagnostic tools for Zika – the Zika MAC-ELISA and Trioplex Real-Time RT-PCR Assay.