Flaviviruses

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Electron micrograph of a flavivirus
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Flavivirus is a genus of viruses in the family Flaviviridae. This genus includes several important human pathogens, such as the Dengue virus, Zika virus, West Nile virus, Yellow fever virus, and Japanese encephalitis virus. Flaviviruses are primarily transmitted through arthropod vectors, such as mosquitoes and ticks, and are responsible for a range of diseases in humans and animals.

Structure

Flaviviruses are small, enveloped viruses with a single-stranded, positive-sense RNA genome. The genome is approximately 10,000 to 11,000 nucleotides in length and encodes a single polyprotein, which is cleaved into three structural proteins (C, prM, and E) and seven non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). The envelope protein (E) is responsible for virus attachment and entry into host cells and is a major target for neutralizing antibodies.

Transmission

Flaviviruses are primarily transmitted to humans through the bite of infected mosquitoes or ticks. The most common mosquito vectors are species of the genera Aedes and Culex. For example, the Dengue virus and Zika virus are primarily transmitted by Aedes aegypti and Aedes albopictus mosquitoes, while the West Nile virus is transmitted by Culex mosquitoes. Tick-borne flaviviruses, such as the Tick-borne encephalitis virus, are transmitted by Ixodid ticks.

Pathogenesis

Upon transmission to a human host, flaviviruses initially replicate at the site of entry and in regional lymph nodes. They can then spread to other tissues, including the liver, spleen, and central nervous system, depending on the virus. The clinical manifestations of flavivirus infections can range from mild febrile illness to severe disease, including hemorrhagic fever and encephalitis. For example, Dengue fever can progress to Dengue hemorrhagic fever, while West Nile virus infection can lead to West Nile encephalitis.

Diagnosis

Diagnosis of flavivirus infections is typically based on clinical presentation, epidemiological factors, and laboratory testing. Laboratory tests include serological assays to detect virus-specific antibodies (such as IgM and IgG) and molecular techniques like reverse transcription-polymerase chain reaction (RT-PCR) to detect viral RNA.

Prevention and Control

Prevention of flavivirus infections primarily involves vector control measures, such as reducing mosquito breeding sites, using insect repellent, and wearing protective clothing. Vaccines are available for some flaviviruses, such as the Yellow fever vaccine and the Japanese encephalitis vaccine. Research is ongoing to develop vaccines for other flaviviruses, including Dengue and Zika.

Also see

• Flaviviridae
• Dengue virus
• Zika virus
• West Nile virus
• Yellow fever virus
• Japanese encephalitis virus
• Tick-borne encephalitis virus