The Flavivirus Life Cycle

Flaviviruses are a genus of RNA viruses in a class of viruses called Arboviruses, which are transmitted by the bite of arthropod vectors. The genus includes over 70 species, many causing disease in humans. Flaviviruses are known for causing St. Louis encephalitis, yellow fever, dengue fever and West Nile fever. They can cause mild disease or rapidly fatal disease with encephalitis and hemorrhage.

Vertebrate Host and Arthropod Vector

• For a successful life cycle, flaviviruses must be able to live and replicate in both the vertebrate host and the blood-sucking arthropod vector, specifically mosquitoes and ticks. Only female mosquitoes transmit flaviviruses because only female mosquitoes need blood meals to produce progeny.

Transmission to Arthropod Vector

• An arthropod vector becomes infected with the virus after biting an infected vertebrate host, if the virus titer in the host's blood is high enough to transmit the virus.

Replication

• The virus infects the arthropod vector, replicating in the arthropod's gut. The virus then spreads to other organs and particularly the salivary glands.

Transmission to Vertebrate Host

• Once the virus is the salivary glands, the infected arthropod vector is able to transmit the virus to a vertebrate host. Humans are usually dead-end hosts because the virus is unable to replicate to create a high enough titer to re-infect the vector; the most successful hosts are monkeys, bats, birds and some domestic animals.

Treatment

• Successful treatment would require interfering with the viral life cycle. For flaviviruses, however, there are no specific antiviral treatments available, which is why West Nile virus is a public health concern.