The Zika virus (ZIKV) was first isolated in 1947 from a rhesus macaque monkey from the Zika forest in Uganda. It is a single-stranded RNA virus belonging to the virus family Flaviviridae and the genus Flavivirus, and is related to the dengue, yellow fever, chikungunya, and West Nile viruses. Its vector of transmission is the female Aedes aegypti mosquito. Transmission between humans can occur through sexual intercourse; blood transfusion; and mother-to-child vertical transmission via pregnancy, delivery, or breast milk.
The first evidence of human infection was discovered in Uganda in 1952. Few cases were identified until an outbreak in Yap, Micronesia, in 2007. Subsequently, the virus was documented in the Americas via the Pacific Islands when an outbreak occurred in Brazil in 2015. Since then, over 1.5 million individuals have been infected with ZIKV in Brazil.
The symptoms of Zika virus infection in adults are mild and self-limited; many individuals infected with ZIKV are asymptomatic. Symptoms include nonspecific fever, joint and muscle pain, conjunctivitis, and rash.
In northeastern Brazil, a sharp rise in the number of infants born with microcephaly (head circumference < 32 cm) occurred 6 months after the onset of the Zika outbreak. The Zika virus is identified via PCR and serologic testing, which was not readily available in parts of Brazil. Therefore, the association between ZIKV and microcephaly was presumptive. In 2015, 29 infants with microcephaly and a presumed diagnosis of congenital ZIKV infection underwent ophthalmologic examination. The most common vision-threatening ocular abnormalities identified were focal pigment mottling of the retina, chorioretinal atrophy, optic nerve abnormalities, bilateral iris coloboma, and lens subluxation.
Since the 2015 Brazil outbreak, vector-borne transmission of ZIKV infection has been reported in 84 countries, territories, or subnational areas. Recently, the term congenital Zika syndrome (CZS) was coined to describe the devastating ophthalmological, neurological, skeletal, and audiological effects the virus exacts on the developing fetus. The most common ocular findings in infants with CZS are chorioretinal atrophy and pigment mottling in the macula similar to that seen in eyes with toxoplasmosis. Zika virus vaccines are currently in development; it remains unknown whether an approved vaccine will protect against CZS. Therefore, when examining microcephalic infants in affected areas, ophthalmologists should be aware of the ocular manifestations of suspected congenital ZIKV infection.
de Paula Freitas, B, de Oliveira Dias JR, Prazeras J, et al. Ocular findings in infants with microcephaly associated with presumed Zika virus congenital infection in Salvador, Brazil. JAMA Ophthalmol. 2016;134(5):529–535.
Marquezan MC, Ventura CV, Sheffield JS, et al. Ocular effects of Zika virus—a review. Surv Ophthalmol. 2018;63(2):166–173.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.