Study: Zika could reach 2.6 billion people

Beijing crowded street
Beijing crowded street

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Two new studies published today present an alarming picture of the potential reach of Zika virus and its complex clinical presentation, while researchers reporting in the latest issue of Eurosurveillance said that Culex mosquitos aren't likely to transmit the virus.

Global at-risk populations

In a study published in the Lancet Infectious Diseases, researchers from the University of Toronto used modeling to identify the areas around the world most at risk for Zika virus. After considering mosquito activity, air travel data and climate information, the researchers said potentially 2.6 billion people living in low-resource parts of Africa and the Asia-Pacific region could be sickened by Zika virus.

"It's a sobering number that highlights the potential magnitude of Zika virus," said Kamran Khan, MD, MPH from St. Michael's Hospital's Li Ka Shing Knowledge Institute in Toronto. "It's not meant to be alarmist, and it may be the worst-case scenario. But Zika is a global epidemic."

Khan said that according the models used, 1.2 billion people in India, 242 million in China, and 197 million in Indonesia are most threatened by Zika. Khan explained that those countries have four factors that put them at risk: high-frequency travel by people from Zika-endemic areas, Aedes mosquito vectors, a climate that sustains mosquito-borne disease, and low public health resources. Using flight data, weather maps and modeling, and population-density maps, Khan and his colleagues were able to assign risk to these countries.

"There's been a lot of attention paid to the risk of Zika in the Americas, the United States, and even Europe," said Khan. "But we see now [in Florida] that even countries with good public health infrastructure suffer a strain of available health and human resources with Zika."

Khan said the major caveat of the study was the unaddressed question of whether or not populations in Africa and parts of Asia have immunity to certain strains of Zika virus.

"Even though we believe the disease originated in Africa," said Khan, "We don't make any assumptions in the study about immunity."

Zika may be clinically confused for dengue

In a related study slated for publication today in the Journal of Clinical Virology, Brazilian researchers suggest that Zika infections may be underestimated and mistakenly reported as infections with other flaviviruses, including dengue.

The researchers based their conclusions on observations made at a Brazilian hospital. Between January and August of this year, the Zika Research Network (Rede Zika) conducted molecular blood tests on 800 people with suspected dengue virus at the Hospital de Base, Sao Jose do Rio Preto's reference hospital.

Only half of those cases (400) were dengue, and 100 were Zika virus. The remaining 300 cases were not related to any arboviruses and were most likely influenza. Currently, the World Health Organization suggests that all suspected cases of dengue be treated as such, because the disease can be much more severe than related flaviviruses.

Mauricio Lacerda Nogueira, MD, PhD, a member of the Zika Research Network, explained the findings in a press release from Sao Jose do Rio Preto Medical School (FAMERP).

"These results suggest the classic division usually made between symptoms—associating conjunctivitis with Zika and joint pain with chikungunya, for example—is only for classroom use. In practice, the symptoms can't be separated like that," Nogueira said. "It's also practically impossible to distinguish between the three arboviruses with the serological tests currently used on a routine basis by laboratories and emergency services."

As of press time the study was not posted on the journal's Web site.

Culex mosquitoes don't transmit Zika

Finally today's issue of Eurosurveillance published a study showing that Culex mosquitoes do not transmit Zika virus. The study appears to disprove a hypothesis that Culex mosquitoes, which are widespread in the Americas, were harboring and spreading Zika virus alongside Aedes vectors.

Two laboratory colonies of Culex species, Cx quinquefasciatus and Cx pipiens, were successfully fed blood containing Zika virus. While some mosquitoes were infected, neither species could transmit the virus at 21 days post-infection.

"On the basis of our results, we consider that vector control should continue to focus on larval and adult habitats specific to Aedes mosquitoes," the authors concluded.

See also:

Sep 1 Lancet Infect Dis abstract

Sep 1 FAMERP press release

Sep 1 Eurosurveill study

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