Presence of Zika Virus in Conjunctival Fluid

Zika virus (ZIKV) is a mosquito-borne flavivirus isolated from the Zika forest of Uganda in 1947.¹ The clinical symptoms of ZIKV infection are mostly a mild and self-limited rash, arthralgia, and conjunctivitis in humans. More than 80% of ZIKV infections are asymptomatic. The ZIKV outbreaks in Brazil and French Polynesia indicate that the virus is linked to microcephaly and Guillain-Barré syndrome.^2,3 Meanwhile, severe eye damage in infants with microcephaly was associated with ZIKV infection.⁴ However, it is still unclear whether the eye lesions are the result of microcephaly or directly ZIKV infection.⁵ Therefore, we wondered whether ZIKV could be detected in conjunctival fluid. In this report, we describe the detection of ZIKV from conjunctival swab samples of laboratory-confirmed ZIKV cases.

Since February 12, 2016, 11 ZIKV infection cases (Chinese travelers) were imported from Venezuela in Guangdong, China (http://www.gdwst.gov.cn/a/yiqingxx). All the cases were confirmed to be ZIKV infection by real-time reverse-transcription polymerase chain reaction (rRT-PCR) (DAAN gene, Guangzhou, China). The virus load was determined using a standard curve with serial dilutions of known plasmid concentrations. The serum and conjunctival swab samples were taken from 6 of 11 cases simultaneously. When evaluated by the institutional review board of the Guangdong province Center for Disease Control and Prevention, this activity was considered a component of the public health response to the imported Zika case in Guangdong; thus, it did not require review. However, each written epidemiology and sampling investigation report was approved by each case.

The results of rRT-PCR for ZIKV in serum of these 6 cases with estimated ZIKV RNA loads ranged from 9.9 × 10² to 2.31 × 10⁶ copies/mL (Table). The conjunctival swab samples from the 6 cases were washed with 800 μL of minimum essential medium. Two hundred–microliter washing solution was used for the rRT-PCR tests. The results demonstrated ZIKV RNA in these samples with a virus load from 1.99 × 10³ to 1.788 × 10⁶ copies/mL (Table). The ZIKV RNA was detectable in serum no more than 5 days after symptom onset, but it was detected in conjunctival swab samples until day 7 in case 5. Thereafter, the ZIKV nucleic acid–positive serum and conjunctival swab samples were subjected to virus culture using neonatal mice (BALB/c, aged 1-3 days) brain injection methods. The presence of ZIKV was detected by rRT-PCR as described earlier. Three ZIKV strains, 2 from serum samples (cases 2 and 3, GDZ16006 and GDZ16019) and 1 from conjunctival swab (case 5, GDZ16020), were successfully isolated from neonatal mice brains. A partial ZIKV NS5 gene (approximately 960 base pairs) was successfully amplified and sequenced from these isolations. Phylogenetic analysis was performed to compare with 60 available ZIKV NS5 genes on GenBank using the software Molecular Evolutionary Genetics Analysis version 6.06 (MEGA). Phylogenetic analyses showed that all the strains belong to the Asian lineage of ZIKV and are closely related to those reported from Brazil, Puerto Rico, and Suriname in 2015 (Figure).

Detection of ZIKV RNA is a gold standard of confirmation of ZIKV infection. In this study, we described the direct detection and isolation of ZIKV from conjunctival swab samples. Although isolation of ZIKV in cell culture from urine, semen, saliva, and breast milk has been described,⁶ to our knowledge, detection and isolation of ZIKV from conjunctiva has not been reported so far. These results, though, are not sufficient to recommend the use of conjunctival swabs as alternative samples for ZIKV diagnosis because of shorter persisting and shedding time of ZIKV in conjunctiva fluid (<7 days) compared with urine and saliva samples (<20 days). It may have implications for transmission of ZIKV, eg, through corneal graft donors, although this report does not provide direct evidence to support that indication. Nevertheless, epidemiological data and experimental studies are needed to assess the further significance of this finding because of increasing complications caused by ZIKV infection in neonates.

Corresponding Author: Changwen Ke, PhD, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou 510300, People’s Republic of China (kecw1965@aliyun.com).

Published Online: September 15, 2016. doi:10.1001/jamaophthalmol.2016.3417

Author Contributions: Dr Ke had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Drs Sun and Wu contributed equally to this work.

Concept and design: Sun, Wu.

Acquisition, analysis, or interpretation of data: Ke, Sun, Zhong, Guan, Zhang, Tan.

Drafting of the manuscript: Ke, Sun, Guan, Zhang, Tan.

Critical revision of the manuscript for important intellectual content: Wu, Zhong.

Statistical analysis: Sun.

Administrative, technical, or material support: All authors.

Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.

Additional Contributions: We thank all the related laboratory and administrative personnel at Guangdong Provincial Center for Disease Control and Prevention and Jiangmen Center for Disease Control and Prevention for their contribution in follow-up investigation.