HEALTH

Canadian study maps countries where Zika virus could hit hardest

Josh Dehaas CTVNews.ca Writer

Published Thursday, September 1, 2016 5:44PM EDT Last Updated Thursday, September 1, 2016 7:04PM EDT

A worker fumigates drains and the gardens at a local housing estate where the latest case of Zika infections were reported from in Singapore on Thursday, Sept. 1, 2016. (AP Photo/Wong Maye-E)

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A new Canadian-led study has mapped the countries in Africa, Asia and the Pacific that face the biggest risk from the strain of Zika virus currently affecting most countries in the Americas, particularly Brazil.

So far, local transmission of the virus in those regions has been noted only in Cape Verde in Africa, Singapore in Asia and some islands in the Pacific, but the scientists estimate 2.6 billion people are at risk.

The researchers, including Dr. Kamran Khan, an infectious disease physician at St. Michael’s Hospital in Toronto, considered a number of factors, including:

the numbers of passengers travelling by airplane in 700 cities
the number of days per year when the countries’ climates would allow Zika-spreading species of mosquito to transmit the virus
the ability of the nations’ public health systems to respond
the numbers of people living in zones suitable to Zika transmission
past outbreaks of Dengue, which appears to spread in a similar fashion

They ran three scenarios. In the most conservative scenario, they found that the 10 countries with the greatest risks of exposure are:

India (1.2 billion at risk in peak month)
China (240 million at risk in peak month)
Indonesia (197 million at risk in peak month)
Nigeria (179 million at risk in peak month)
Pakistan (168 million at risk in peak month)
Bangladesh (163 million at risk in peak month)
Vietnam (83 million at risk in peak month)
Philippines (70 million at risk in peak month)
Thailand (59 million at risk in peak month
Burma (51 million at risk in peak month)

Their least conservative scenario is much the same, but with more than 1.1 billion people affected in China.

Dr. Khan told CTVNews.ca that his team chose to focus on Asia, Africa and the Pacific because they are the least technologically and financially prepared to deal with the virus.

He said India is particularly worrying because of its huge population living with climates favourable to the spread of the virus, not to mention the fact that there is plenty of standing water in which mosquitos can breed.

“Hopefully we will not see the same kind of situation as occurred in Brazil,” Dr. Khan said of India.

Dr. Khan said the results have implications for the international community, the countries involved and Canadian travellers.

In terms of the countries studies, he points out that their month-by-month analysis will let officials know when to spend their finite resources.

Click the arrows in the slideshow to advance to the next map.

Source: St. Michael's Hospital in Toronto / Dr. Kamran Khan

For example, the researchers found September is when the climate in Vietnam is most favourable to the spread of Zika, and it also happens to be the peak period of travel flows from Zika-affected cities, so public health officials should be on high alert this month.

Dr. Khan said organizations like the World Health Organization can also use the data, in order to show that this may be “a global epidemic.”

Canadians need to know that they may be at risk if they travel to these countries, particularly if they are pregnant or planning to become pregnant. Zika virus has been linked to the birth defect microcephaly.

Dr. Khan notes there are some big caveats to the work, the most important of which is that people in Asia and Africa may have some genetic immunity to the virus, developed from past outbreaks. He said there is no research yet that can answer that question, adding “I think the approach should be prepare for the worst and hope for the best.”

The findings are published in the September issue of The Lancet Infections Diseases.