As Zika cases continue to pop up in Florida, a lot of the anxiety around the virus has understandably been focused on the disease’s future in the United States. Will Zika spread to other states? Will congressional lawmakers finally allocate funds for Zika research, detection, and prevention when they return from summer break?
But the narrow US focus misses where the real Zika threat lies. The worst Zika outbreaks right now are happening outside of the continental United States, in places like Puerto Rico. And the countries at risk of serious outbreaks in the future are even further afield, in Africa and Asia.
A new study published in The Lancet Infectious Diseases seeks to figure out where the virus circulating in the Americas is most likely to land next.
Robust travel to and from Zika-affected countries, high numbers of the Zika-carrying Aedes aegypti mosquitos, and impoverished health systems are the ingredients of a Zika outbreak. The study took these factors into account and plotted African and Asian countries on the following graph, which shows their relative Zika risk:
Among the places most likely to see outbreaks in the coming months are India, China, the Philippines, Indonesia, Nigeria, Vietnam, Pakistan, and Bangladesh.
"Many of [these] areas have a rather limited health [care] capacity," said Isaac Bogoch, study author and infectious diseases specialist at the Toronto General Hospital. "These countries might be slow to detect the virus — and they might not have the capabilities to do mosquito surveillance, mosquito-control efforts, or perhaps provide appropriate maternal screening and management for pregnant women affected with the virus."
The researchers estimate that up to 5,000 passengers per month will be arriving from Zika-endemic regions in the Americas to India, Indonesia, and Nigeria. Singapore is already dealing with an outbreak involving more than 100 cases, including pregnant women, while nearby Indonesia braces for an outbreak.
"This virus could have been imported [to Singapore] sometime in July or August," Bogoch said. And if health officials have found Zika in a high-income country like Singapore, he added, it may already be circulating, undetected, in other Asian countries.
"Should Zika be imported into these areas, the impact on their health systems could be very severe," said study author Oliver Brady, a research fellow at the London School of Hygiene & Tropical Medicine, in a statement.
That said, there’s a lot that’s still unknown about this virus.
One of the assumptions in the model is that people in these countries have no preexisting immunity to Zika. But if that’s wrong, it would mean populations might not be as susceptible to outbreaks, since researchers believe a previous infection with the virus confers lifelong immunity.
"We don’t know how widespread Zika was in these countries," Bogoch said.
They also don’t know whether an infection with the circulating Asian strain (currently going around the Americas) will protect people from Zika’s African strain.
If these models are correct, however, we might find out very soon — which will mean Zika will be with us for a while.