Urban transmission of mosquito-borne flaviviruses – a review of the risk for humans in Vietnam

ABSTRACT

Vietnam is a tropical country where mosquito-borne diseases are common. This review explores the transmission of mosquito-borne flaviviruses in urban areas of Vietnam. It concludes that urban transmission has mainly been studied for Dengue virus, and so far, much less for Japanese encephalitis virus. Dengue is the most common flavivirus in Vietnam. Due to fast urbanization and favorable climatic conditions, the viral transmission concentrates mainly to large cities with high population density including Ha Noi, Nha Trang and Ho Chi Minh. Human cases of Japanese encephalitis have been controlled by an expanded immunization program. However, this virus is still circulating throughout the country, also in cities due to the pig rearing practices in urban and peri-urban areas. Zika virus is an additional major concern because it has long circulated in the Northern area and is now increasingly diagnosed in urban areas of the Central, Central Highlands and Southern regions using the same mosquito vectors as Dengue virus. There was alarge outbreak of Zika disease from 2016 to early 2017, with most infections observed in Ho Chi Minh city, the largest town in Vietnam. Other flaviviruses circulate in Vietnam but have not been investigated in terms of urban transmission.

KEYWORDS:

• Mosquito-borne flavivirus
• Dengue virus
• Zika virus
• Japanese encephalitis virus
• urban transmission
• Vietnam

Acknowledgments

We would like to thank Dr Vu Trong Duoc from National Institute of Hygiene and Epidemiology, Vietnam for providing us with essential data for writing.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was was funded by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas, grant number 2016-00364).

Notes on contributors

Thang Nguyen-Tien

Thang Nguyen-Tien is a PhD fellow of International Livestock Research Institute and Uppsala University, following the research track of Infection since 2018. He is focusing on one health approach to deal with vector-borne and infectious diseases in his PhD project.

Åke Lundkvist

Åke Lundkvist is a Professor in Virology. He is the co-founder and head of the Zoonosis Science Center (ZSC) at Department of Medical Biochemistry and Microbiology, Uppsala University, Sweden. His research group is focused on viral zoonoses, with a specifc interest in hanta-, favi- and avian infuenza viruses. His research has included basic virology, immunology, genetics, molecular epidemiology, animal models, virus evolution, antivirals and diagnostics.

Johanna Lindahl

Johanna Lindahl is a veterinary epidemiologist working at the International Livestock Research Institute (ILRI) in Hanoi, Vietnam, and is an associate professor at Uppsala University since 2017. Johanna graduated from the Swedish University of Agricultural Sciences after doing her PhD working on Japanese encephalitis virus in Vietnam. Since her PhD she has been focusing her research on food safety, and vector-borne, zoonotic and emerging infectious diseases in developing countries.