Researchers develop a detailed map of the suitability for Zika virus occurrence worldwide, and identify the most important factors for the spread of the disease

Study published in the journal Memórias do Instituto Oswaldo Cruz maps the global potential for spread of Zika virus, and points out factors that impact risk of transmission in a global grid of approximately 5 x 5 km. The map notes several countries as being at risk, including Singapore, where nearly 400 cases have been recorded in an outbreak of the virus. Other countries identified as at risk in Asia include Thailand, southern China, India, and Bangladesh. This map summarizes not only the potential of these areas for Zika transmission, but also identifies major drivers of transmission around the world.

"If the virus is introduced in Singapore, all factors are in place for autochthonous transmission of Zika virus. We could expect the virus to spread across Singapore and neighboring countries in the region very quickly, unless local and international health authorities implement effective control programs in the area" says the lead researcher, Dr. Abdallah Samy, researcher at the Faculty of Science at Ain Shams University, in Egypt, and recent doctoral graduate of the Biodiversity Institute at the University of Kansas, in the USA.

To map the potential for Zika virus spread, the researchers took into account the main factors that may affect the transmission of the disease, including not only the presence of vectors, appropriate climate conditions, and environmental characteristics, but also socioeconomic conditions and accessibility. Observing the regions where the disease initially spread in the Americas and data such as population density, daytime and nighttime temperature, land cover and accessibility via transportation, the researchers constructed a mathematical model that allowed them to identify areas with highest risk of transmission and also the factors associated with outbreaks of the disease. The work also included collaboration of researchers from the Universities of Bayreuth and Georg-August, in Germany, and the Mayo Clinic, in the United States.

Considering the regions where the Zika virus has not yet spread, the research points out that parts of Australia, Melanesia, and New Zealand present most or all risk factors for Zika virus spread. In the United States, Florida, Texas, and Louisiana are also at high risk, with all risk factors for outbreak in place. However, elsewhere in the United States, other scattered and narrow areas are at risk across other states, particularly as a function of socioeconomic and travel-based factors.

“Zika outbreaks tend to be less explosive in the United States than in other regions of the Americas. There are better programs for mosquito control in parts of the country and many houses in high-risk areas have screened windows and air conditioning,” says Dr. Townsend Peterson, researcher at the Biodiversity Institute at the University of Kansas, in the United States. He emphasizes the importance of vector control and educational programs, as well as monitoring travel-mediated importation of the virus, in these risk areas, as an important element in reducing risk.

A large region with high potential for the disease is also noted in sub-Saharan Africa. However, the researchers emphasize that the African continent presents a different situation, making predictions more difficult. Discovered in Zika forest in Uganda in 1947, the Zika virus has two strains: one African and one Asian, the latter of which is behind the current outbreaks in the Americas and Asia. "Africa has a previous history of exposure to Zika, and population immunity can be integral in shaping where and how the virus could spread across Africa. Such questions can be integrated into future, more complex models, for a better understanding of the future of the outbreak in these regions,” explains Samy.

The study also showed that, in Europe, despite high connectivity to regions with Zika transmission, which facilitates arrival of infected travelers, few places present favorable environmental conditions for the spread of the disease, considering the presence of insect vectors and climate. The study authors point out that their maps can aid authorities in tackling the virus. "The results allow us to identify priority areas for surveillance of vectors and viruses and the locations where the risk may come from other factors, especially considering that Zika can be transmitted by alternative routes, including by sexual transmission," says Samy.

Maíra Menezes
14/10/2016
Reproduction for noncommercial use is allowed. Credit must be given to Oswaldo Cruz Institute.