Human Anti-Zika Virus IgG ELISA Kit

Principle of the Assay

This assay is an antigen-down enzyme immunoassay where a recombinant Zika Virus NS1 antigen is pre-coated onto a 96-well microplate and used to bind antibodies found in the sample. When the sample is added (such as human serum), antibodies found in the sample that recognize Zika Virus NS1 antigen bind the antigen coated plate and are retained in the well. After washing away unbound substances, an enzyme linked polyclonal antibody specific for human IgG is added to the wells. Following a wash to remove any unbound enzyme linked antibody, a substrate is added to the wells and color develops in proportion to the amount of IgG antibodies in the sample bound to the Zika Virus NS1 antigen. The color development is stopped and the intensity of the color is measured.

The potential for false positives due to Zika Virus NS1 antigen cross-reactive antibodies to related flaviviruses, such as Dengue Virus, is minimized by treatment of the samples. Samples are treated with a propriety treatment reagent prior to being added to the Zika Virus NS1 antigen coated plate. Sample specific background is determined by adding identically treated samples to an uncoated background plate and measuring the amount of IgG antibodies non-specifically bound to the well. To interpret results, net sample readings are calculated by subtracting each sample background plate reading from the Zika Virus NS1 antigen plate reading.

Precision

Intra-Assay Precision (Precision within an assay)

Three Zika Virus IgG antibody positive samples with high, middle, and low net O.D. were tested twenty four times on one plate to assess intra-assay precision.

Inter-assay Precision (Precision between assays)

Three Zika Virus IgG antibody positive samples with high, middle, and low net O.D. were tested in twenty separate assays to assess inter-assay precision. Assays were performed by at least three technicians.

Specificity

This assay recognizes Zika Virus specific human IgG antibodies with minimal cross-reactivity of human Dengue IgG antibodies.

^aZika patient samples were collected from Colombia between 2015 and 2016 and determined to be positive based on EIA testing, according to the sample supplier.

^bWhen tested without Treatment Reagent, these samples test positive for Zika Virus IgG, but are negative following Treatment Reagent treatment, indicating competitors A & E positive result from these samples are false positive.

^cDengue patient samples were collected from Puerto Rico between 2012 and 2013 before Zika was introduced into Puerto Rico. On December 31, 2015, the United States reported the first PCR-confirmed case of locally acquired Zika infection in Puerto Rico.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5034643/

Competitor A, E, and M kits have either high cross-reactivity with Dengue Virus IgG antibody or low sensitivity to Zika Virus IgG antibody. R&D Systems^® Zika Virus IgG ELISA kit has high sensitivity and specificity to Zika Virus IgG antibody.

Background: Zika virus

Zika virus (ZIKV) is a mosquito-borne flavivirus found throughout tropical and subtropical regions, including East Africa, Southeast Asia, and the Pacific Islands, that is now causing large-scale outbreaks in the Americas (1, 2). This continuous geographic expansion of ZIKV poses a serious and increasing public health threat around the globe (1-4). Initially, ZIKV infection was thought to cause only mild illness, however it has now been linked to a rising number of severe neurological abnormalities and diseases including microcephaly, congenital abnormalities, and nonfetal illnesses such as Guillain-Barré syndrome, which emphasizes the importance of accurate ZIKV diagnostics (2, 4-6). Serological diagnosis is complicated by cross-reactivity among members of the Flavivirus genus (6). Because ZIKV, Dengue virus (DENV), and related flaviviruses, co-circulate in endemic regions and share high sequence similarity, there is a high possibility of IgM and IgG cross-reactivity in immunoassays (7). Current or past infections will often cause false positives requiring the need for follow-up testing and confirmation by a plaque-reduction neutralization (PRNT) assay. PRNT is a complicated method that takes considerable time and has limited availability (7, 8). In addition, antibodies present from past infection by Zika or other flaviviruses may enhance the risk of future ZIKV infections through antibody-dependent enhancement (ADE), which may lead to increased disease severity (9). There is a need for a simple serological test that displays high Zika specificity with minimal cross-reactivity with other flaviviruses.

References:

1. Waggoner, J.J. et al. (2016) J.Clin. Microbiol. 54:860.
2. Song, B.H. et al. (2017) J. Neuroimmunol. 308:50.
3. Fellner, C. (2016) PT. 41:778.
4. Althouse, B.M. et al. (2016) PLoS Negl. Trop. Dis. 10:e0005055.
5. Krauer, F. et al. (2017) PLoS Med. 14:e1002203
6. Musso, D. et al. (2016) Clin. Microbiol. Rev. 29:487.
7. Cabral-Castro, M.J. et al. (2016) J. Clin. Virol. 82:108.
8. Sharma, A et al. (2017) Front. Microbiol. 8:110.
9. Paul, L.M. et al. (2016) Clin. Transl. Immunol. 5:e117.