What is the geographical distribution of the Zika virus?

Geographical Distribution of Zika Virus

Zika virus has expanded from its origins in Uganda to become widespread throughout Africa, Asia, the Pacific Islands, and the Americas, with current active circulation in Latin America, parts of the Pacific Islands, and Southeast Asia. 1

Historical Spread and Origins

• Zika virus was first isolated in Uganda in 1947, with only sporadic cases identified in Africa and Asia for approximately 60 years 2
• The virus belongs to the flavivirus family and is closely related to dengue, yellow fever, Japanese encephalitis, and West Nile viruses 1
• The first major outbreak was recognized in Micronesia in 2007, marking the beginning of its geographical expansion beyond Africa and Asia 2
• During 2013-2015, approximately 30,000 suspected Zika virus cases were reported from French Polynesia and other Pacific islands 2
• A large-scale outbreak occurred throughout much of the Americas during 2015-2016, representing significant geographical expansion 2

Current Geographic Distribution

• Zika virus is actively circulating in:
  • Much of Latin America and the Caribbean 1
  • Parts of the Pacific Islands 1
  • Southeast Asia 1
• The virus has been isolated in Africa in mosquitoes of the genera Aedes, Anopheles, and Mansonia 3
• In Southeast Asia and the Pacific area, the virus has primarily been isolated in mosquitoes of the genus Aedes 3

Transmission Vectors and Their Distribution

• Zika virus is transmitted primarily by Aedes species mosquitoes, particularly Aedes aegypti, which are present throughout the tropics and subtropics 2
• Aedes albopictus (Asian tiger mosquito) has invaded several countries in Central Africa, all Mediterranean countries, and continues to spread throughout Central and Northern Europe 3
• The primary vector, Aedes aegypti, is a day-biting mosquito that is widely distributed in tropical and subtropical regions 4

Genetic Lineages and Geographic Variants

• Phylogenetic analyses have revealed the existence of two main virus lineages: African and Asian 5
• The strain responsible for the Yap epidemic and later Cambodian cases most likely originated in Southeast Asia 5
• The basal position of the ZIKV strain isolated in Malaysia in 1966 suggests that the outbreak in Micronesia was initiated by a strain from Southeast Asia 5

Population at Risk

• An estimated 2.6 billion people live in areas of Africa and the Asia-Pacific region where competent mosquito vectors and suitable climatic conditions could support local transmission of Zika virus 6
• Countries with large populations at risk and significant travel connections to affected areas include:
  • India (1.2 billion residents in potential transmission areas)
  • China (242 million residents)
  • Indonesia (197 million residents)
  • Philippines (70 million residents)
  • Thailand (59 million residents) 6

Transmission Modes Beyond Mosquitoes

• Beyond vector-borne transmission, Zika virus can spread through:
  • Congenital transmission (mother to fetus) 2
  • Perinatal transmission 2
  • Sexual transmission 2
• These additional transmission routes contribute to the virus's ability to spread beyond areas where the vector is present 2

Clinical Significance of Geographical Distribution

• The geographical spread of Zika virus has been associated with:
  • Increased incidence of Guillain-Barré syndrome in affected regions 2
  • Outbreaks of microcephaly and other congenital abnormalities in newborns 2
  • Various neurological disorders including encephalitis, encephalopathy, and myelitis 2

Monitoring and Surveillance

• Up-to-date information on areas where there is risk for Zika virus infection and ongoing outbreaks is available through online resources maintained by health authorities 2
• International disease surveillance initiatives help identify new outbreaks and monitor the geographical spread of the virus 2
• The widespread distribution of the virus in animal hosts and vectors increases the risk of recombination events and potential emergence of new variants 3

Risk Factors for Further Geographical Expansion

• The omnipresence of Aedes vectors in many regions creates potential for further spread 7
• Climate suitability plays a significant role in determining areas at risk for Zika transmission 6
• International air travel from affected areas contributes significantly to the risk of importation and local spread 6