Flaviviruses – new human pathogens

The family Flaviviridae includes arthropod-borne viruses that are transmitted to vertebrates by infected mosquitoes and ticks. There are over a 100 species in this family, most of which are animal pathogens, although it cannot be excluded that some animal flaviviruses will also cause human disease. The family name is due to the discovery of the yellow fever virus and is derived from the Latin word flavus, meaning yellow. Several human-pathogenic flaviviruses have a significant public health impact in different parts of the world and the potential of emerging in previously non-endemic regions. The medically important flaviviruses include among others: dengue, Zika, yellow fever, tick-borne encephalitis (TBE) and West Nile viruses. Diseases that are caused by these viruses include a spectrum of illnesses ranging from asymptomatic infections to severe and fatal disease. Although the characteristics of these viruses are well defined, they are still unpredictable with increases in disease severity, unusual clinical manifestations, unexpected methods of transmission, long-term persistence, and the discovery of new species. This review compares the epidemiological and clinical features of the medically important flaviviruses and considers the effect of human activity on their evolution and dispersal. Climate change, urbanization and increasing ease of travel have created opportunities for the vector to spread and expand into new human populations. The combination of these factors makes it possible for the family Flaviviridae to change and emerge quickly as a new, potential human pathogen.