Zika virus
Summary
Zika virus is a flavivirus transmitted primarily by Aedes mosquitoes, also spread via sexual contact and vertically from mother to fetus. Infection is often asymptomatic or causes mild febrile illness with rash, conjunctivitis, and arthralgia, but is notably associated with congenital microcephaly and Guillain-Barré syndrome. It is a high-yield board topic due to its teratogenic potential.
Detail
Zika virus is a single-stranded, positive-sense RNA virus in the Flaviviridae family, related to dengue, West Nile, and yellow fever viruses. It is transmitted mainly by Aedes aegypti and Aedes albopictus mosquitoes, but unique among flaviviruses for its documented sexual transmission (can persist in semen for months) and vertical transmission across the placenta.
Clinical presentation: Most infections (~80%) are asymptomatic. Symptomatic cases present with low-grade fever, maculopapular rash, conjunctivitis (non-purulent), arthralgia, and myalgia—self-limited, lasting less than a week. This tetrad (fever, rash, conjunctivitis, arthralgia) is a classic USMLE association.
Key complications: 1. Congenital Zika syndrome: Maternal infection, especially in the first trimester, can cause severe fetal microcephaly, intracranial calcifications, ventriculomegaly, and other brain anomalies due to viral tropism for neural progenitor cells. This is the most tested association on boards. 2. Guillain-Barré syndrome: Zika infection is a recognized trigger for this post-infectious autoimmune polyneuropathy, presenting with ascending flaccid paralysis due to molecular mimicry and immune-mediated demyelination of peripheral nerves.
Diagnosis: RT-PCR detects viral RNA in serum/urine during acute infection (first 1-2 weeks). Serology (IgM ELISA) can be used later but cross-reacts with other flaviviruses (dengue, especially in previously vaccinated or infected individuals), often requiring confirmatory plaque reduction neutralization test (PRNT).
Management: Supportive care only; no specific antiviral treatment or vaccine is currently approved. Prevention focuses on mosquito control, barrier contraception, and travel advisories for pregnant women to endemic areas (parts of Latin America, Caribbean, Southeast Asia, Africa).
Differential diagnosis on boards often includes distinguishing Zika from dengue and chikungunya, which share vector and geographic overlap but differ in presentation (dengue: severe myalgia/hemorrhagic risk; chikungunya: severe polyarthralgia).
Sources
- First Aid for the USMLE Step 1
- CDC Zika Virus Clinical Guidance
- Harrison's Principles of Internal Medicine
- Sherris Medical Microbiology
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.