London School of Hygiene & Tropical Medicine

New information on how and when the Zika virus might have entered the Americas has been revealed, in a genomic study published in the journal Science.

The research, led by the University of Oxford with international partners, analysed Zika virus genome sequence data to show that the first human infection with Zika was detected in November 2015, while introduction to Brazil probably occurred between May-December 2013. The study also looked at patterns of air travel in the region, and investigated the correlation in time and space between Zika and the congenital birth defect microcephaly.

Commenting on the study, Martin Hibberd, Professor of Emerging Infectious Diseases at the London School of Hygiene & Tropical Medicine, said:

"This paper is the first to publish whole genome data from Zika virus in Brazil. It gives good new insights into the outbreak such as the predicted introduction time, although the number of genomes reported is very small. Many more are needed to get a more comprehensive picture of how the virus is spreading through Brazil and South America. Although not conclusive, it is an important step towards future work that will allow us to understand this outbreak in greater detail - work that will hopefully lead to more accurate intervention strategies.

"The introduction of one Zika virus leading to a widespread outbreak may seem surprising. However the modelling of other Zika outbreaks, and also the highly related dengue outbreaks, suggest that this is not unusual. In the right conditions, with sufficient mosquitoes and closely packed humans, the virus can spread rapidly.

"Given the amount of human travel between countries, any region with dengue could suffer from Zika. That means 3.6 billion people from the tropical regions are at potential risk. However the UK is not one of them. Our colder climate means the mosquitoes which transmit Zika and dengue are not found here. So, although it seems that in rare cases there can be sexual transmission of Zika, the UK is highly unlikely to experience a Zika epidemic. The cases seen in the UK will be from travellers returning from countries affected by Zika."

Dr Adam Kucharski, Research Fellow in Infectious Disease Epidemiology at the School, said:

"If Zika was introduced to Brazil in mid-2013 it suggests the virus has been circulating undetected for a long period of time: the first case reports in the country were in 2015. Similar infections like dengue fever also circulate in the region, so Zika infection can often be misdiagnosed.

"This could make it harder to understand the potential relationship between Zika, microcephaly and other neurological complications in South America and other regions. The analysis demonstrates the importance of collecting and analysing genome sequence data in real time."

Related links:

• Zika virus outbreak and related research
• Media highlights: latest opinion from our experts in the news