Imagine a virus so serious the government recommends that women stop getting pregnant.

It exists, and it is now in Brazil, which is a big concern as the Olympics approaches. The Zika virus, native to parts of Africa and Asia, has been spreading locally among people who have not traveled abroad. There is no vaccine against the virus or antiviral treatment.

Zika is generally a mild illness, spread by a day-biting mosquito. However, there is a worrisome, but as of yet unproven, association of infected mothers in Brazil giving birth to babies with small heads and underdeveloped brains, Dr. Khan said. There has been a 20-fold increase in the number of babies born with this condition, known as microcephaly, since Zika first appeared in Brazil in May 2015.

The virus has since spread across more than a dozen countries in South and Central America and up into Mexico. A case was confirmed in Puerto Rico in December in an individual who had not recently traveled, meaning he or she was bitten by a local infected mosquito. The Centers for Disease Control say some travelers returning to the United States from Zika-affected areas have also been infected with the virus, which has the potential of allowing the virus to then spread locally. 


Dr. Kamran Khan. Credit: Courtesy of St. Michael's Hospital

To predict where Zika might spread,  Dr. Kamran Khan of St. Michael's Hospital mapped the final destinations of international travelers leaving airports in Brazil from September 2014 to August 2015.

Of those 9.9 million travelers, 65 percent were going to the Americas, 27 percent to Europe and 5 percent to Asia. Traveler volumes were greatest to the United States, followed by Argentina, Chile, Italy, Portugal, and France. China and Angola received the highest volume of travelers in Asia and Africa, respectively.

Members of the team from Oxford University mapped the global geography of (Aedes species) mosquitoes capable of transmitting Zika virus and then modeled the worldwide climate conditions necessary for the virus to spread between Aedes mosquitoes and humans. They estimated that more than 60 percent of the populations of the United States, Argentina and Italy live in areas conducive to seasonal transmission of Zika virus. By comparison, Mexico, Colombia and the United States have an estimated 30.5 million, 23.2 million and 22.7 million people respectively living in areas conducive to year-round Zika virus transmission.

Since there is no vaccine or antiviral therapy available, possible interventions include personal protection (i.e., repellent use), daytime avoidance of mosquito bites (especially by pregnant women until more is known about the association between Zika virus infection and microcephaly) and community-level mosquito surveillance and control measures.

"The world we live in is very interconnected now said Dr. Isaac Bogoch, a tropical infectious disease specialist at the Toronto General Hospital who contributed to the study. "Things don't happen in isolation anymore. Infections from the farthest corners of the world can quickly arrive on our doorstep."

source: St. Michael's Hospital