Flaviviridae
Summary
Flaviviridae is a family of enveloped, positive-sense single-stranded RNA viruses transmitted primarily by arthropod vectors (mosquitoes, ticks). Key members include Dengue, Zika, Yellow Fever, West Nile, and Hepatitis C viruses. These viruses cause a spectrum of disease from hepatitis to hemorrhagic fever and encephalitis.
Detail
Flaviviridae are small, enveloped viruses with a positive-sense, single-stranded RNA genome that is translated as a single polyprotein, later cleaved by viral and host proteases into structural (capsid, envelope) and nonstructural proteins. Most flaviviruses (except HCV) are arboviruses transmitted by mosquitoes or ticks, replicating in both the vector and vertebrate host.
Key pathogens and associations (high-yield for boards): - Dengue virus: causes dengue fever, and severe dengue/dengue hemorrhagic fever/shock syndrome upon secondary infection with a different serotype (antibody-dependent enhancement). Transmitted by Aedes aegypti mosquitoes. Presents with fever, retro-orbital pain, rash, thrombocytopenia, and hemoconcentration. - Zika virus: transmitted by Aedes mosquitoes and sexual contact; associated with congenital microcephaly and Guillain-Barré syndrome. Often mild or asymptomatic in adults. - Yellow fever virus: transmitted by Aedes mosquitoes in Africa/South America; causes fever, jaundice (hepatitis), and hemorrhagic manifestations. Classic finding: Councilman bodies (apoptotic hepatocytes) on liver biopsy. Vaccine-preventable (live attenuated). - West Nile virus: transmitted by Culex mosquitoes, birds as reservoir; causes meningoencephalitis, especially in elderly/immunocompromised, sometimes with flaccid paralysis. - St. Louis encephalitis virus, Japanese encephalitis virus: cause encephalitis, JEV vaccine-preventable. - Hepatitis C virus (HCV): unique in that it is NOT arthropod-borne; transmitted via blood/blood products, IV drug use, and less commonly sexually. Causes chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Treated with direct-acting antivirals (e.g., NS5A inhibitors, protease inhibitors, polymerase inhibitors).
Diagnosis: RT-PCR (acute), IgM/IgG serology (later), viral culture in select cases. Cross-reactivity among flaviviruses can complicate serologic testing (e.g., dengue vs Zika).
Clinical relevance: Important to recognize overlapping clinical presentations (fever, rash, arthralgia) among arboviral flaviviruses and distinguish based on travel history, vector exposure, and specific complications (e.g., microcephaly with Zika, hemorrhagic fever with dengue/yellow fever, chronic liver disease with HCV).
Sources
- First Aid for the USMLE Step 1
- Sherris Medical Microbiology
- CDC Yellow Book
- Harrison's Principles of Internal Medicine
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.