Zika virus ‘spreading explosively,’ WHO leader says

Updated 5:43 PM EST, Sat February 20, 2016
View of Aedes aegypti mosquitoes infected with the Wolbachia bacterium --which reduces mosquito transmitted diseases such as dengue and chikungunya by shortening adult lifespan, affect mosquito reproduction and interfere with pathogen replication-- at the Oswaldo Cruz foundation in Rio de Janeiro, Brazil, on October 2, 2014. The mosquitoes, when released, are expected to quickly infiltrate the insect population and stop the spread of the disease. Small-scale trials have already been conducted in communities in northern Australia.
Christophe Simon/AFP/Getty Images
View of Aedes aegypti mosquitoes infected with the Wolbachia bacterium --which reduces mosquito transmitted diseases such as dengue and chikungunya by shortening adult lifespan, affect mosquito reproduction and interfere with pathogen replication-- at the Oswaldo Cruz foundation in Rio de Janeiro, Brazil, on October 2, 2014. The mosquitoes, when released, are expected to quickly infiltrate the insect population and stop the spread of the disease. Small-scale trials have already been conducted in communities in northern Australia.
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MCALLEN, TX - APRIL 14:  A city environmental health worker displays literature to be distrubuted to the public on April 14, 2016 in McAllen, Texas. Health departments, especially in areas along the Texas-Mexico border, are preparing for the expected arrival of the Zika Virus, carried by the aegypti mosquito, which is endemic to the region. The U.S. Centers for Disease Control (CDC), announced this week that Zika is the definitive cause of birth defects seen in Brazil and other countries affected by the outbreak.  (Photo by John Moore/Getty Images)
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MCALLEN, TX - APRIL 14: A city environmental health worker displays literature to be distrubuted to the public on April 14, 2016 in McAllen, Texas. Health departments, especially in areas along the Texas-Mexico border, are preparing for the expected arrival of the Zika Virus, carried by the aegypti mosquito, which is endemic to the region. The U.S. Centers for Disease Control (CDC), announced this week that Zika is the definitive cause of birth defects seen in Brazil and other countries affected by the outbreak. (Photo by John Moore/Getty Images)
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Story highlights

NEW: Canadian agency requests certain travelers wait one month before donating blood

Clinical trials on a vaccine for Zika virus could start this year, U.S. health official says

WHO estimates 3 million to 4 million cases of Zika possible in Americas in 12-month period

(CNN) —  

The Zika virus “is now spreading explosively” in the Americas, the head of the World Health Organization said Thursday, with another official estimating between 3 million to 4 million infections in the region over a 12-month period.

“The level of concern is high, as is the level of uncertainty,” Dr. Margaret Chan, WHO’s director-general, told her organization’s executive board members. “We need to get some answers quickly.”

Five things you need to know about Zika

The lack of any immunity to Zika and the fact that mosquitoes spreading the virus can be found most “everywhere in the Americas” – from Argentina to the southern United States – explains the speed of its transmission, said Dr. Sylvain Aldighieri, an official with the WHO and Pan American Health Organization.

Aldighieri gave the estimate for Zika infections (including people who do not report clinical symptoms) based on data regarding the spread of a different mosquito-borne virus – dengue. He acknowledged the virus is circulating with “very high intensity.”

Some 80% of those infected with the Zika virus don’t even feel sick, and most who do have relatively mild symptoms such as a fever, rash, joint pain or pink eye. But there are major worries about the dangers pregnant women and their babies face.

Chan said that, where the virus has arrived, there’s been a corresponding “steep increase in the birth of babies with abnormally small heads and in cases of Guillain-Barre syndrome.” Having small heads can cause severe developmental issues and sometimes death. Guillain-Barre is a rare autoimmune disorder that can lead to life-threatening paralysis.

The WHO’s Dr. Bruce Aylward cautioned there was no definitive link between Zika and these disorders but sees a legitimate reason for concern. The Centers for Disease Control and Prevention’s Dr. Anne Schuchat said there is a “strong” suggestion they are connected.

Complete Zika virus coverage

While studies are underway to determine any links, millions of people live in areas with real fears about what this virus can do.

Pregnant women, their babies at high risk

After first being detected in 1947 in a monkey in Uganda, Zika was most often found along the equator from Africa into Asia. Nine years ago, new cases popped up in islands in the Pacific Ocean.

The children of Zika: Babies born with disorder linked to virus

Last year, the virus made its way to the Americas – with devastating results.

Since Brazil made its first discovery of Zika in May, the number of cases there and elsewhere in the Americas has grown exponentially. The virus had been thought to be relatively harmless over the long term, but that view changed late last year.

Health authorities began to suspect a connection between Zika and neurological ailments, especially in fetuses and newborns. Brazil alone has reported more than 4,000 cases of microcephaly – a neurological disorder resulting in the births of babies with small heads – in infants born to women infected with Zika while pregnant.

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“Zika is not a new virus,” the CDC’s Schuchat said. “But what we are seeing in the Americas is new.”