The Zika outbreak in South America may have been fuelled by change in weather patterns, brought on by the 'Godzilla' El Nino last year, a new study has found.
El Nino is a climate phenomenon that sees above-normal temperatures in the Pacific Ocean and causes extreme weather around the world.
It occurs every three to seven years in varying intensity, with the 2015 El Nino, nicknamed the 'Godzilla', one of the strongest on record.
Researchers from the University of Liverpool in the UK used a new epidemiological model that looked at how climate affects the spread of Zika virus by both of its major vectors, the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus).
The model can also be used to predict the risk of future outbreaks, and help public health officials tailor mosquito control measures and travel advice.
It used the worldwide distribution of both vectors as well as temperature-dependent factors, such as mosquito biting rates, mortality rates and viral development rates within mosquitoes, to predict the effect of climate on virus transmission.
The model found that in 2015, when the Zika outbreak occurred, the risk of transmission was greatest in South America.
Researchers believe that this was due to a combination of El Nino and climate change, creating conducive conditions for the mosquito vectors.
"It's thought that the Zika virus probably arrived in Brazil from Southeast Asia or the Pacific islands in 2013," said Cyril Caminade, who led the research.
"However, our model suggests that it was temperature conditions related to the 2015 El Nino that played a key role in igniting the outbreak - almost two years after the virus was believed to be introduced on the continent," said Caminade.
"In addition to El Nino, other critical factors might have played a role in the amplification of the outbreak, such as the non-exposed South American population, the risk posed by travel and trade, the virulence of the Zika virus strain and co-infections with other viruses such as dengue," she said.
The World Health Organisation recently declared that Zika, which has been linked to birth defects and neurological complications, will no longer be treated as an international emergency, but as a "significant enduring public health challenge."
"Zika is not going away, and so the development of tools that could help predict potential future outbreaks and spread are extremely important," said Matthew Baylis, from the University's Institute of Infection and Global Health.
"Our model predicts a potential seasonal transmission risk for Zika virus, in the south eastern United States, southern China, and to a lesser extent over southern Europe during summer," said Baylis.
The research was published in the jornal PNAS.
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