You may have heard about the spreading Zika virus, a mosquito borne pathogen that can severely affect pregnant women and their children.

The head of the World Health Organization has called an emergency meeting for Monday to discuss what she is calling a "pandemic" with the virus "spreading explosively" throughout the Americas.

CNN:

"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."

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.

There is also a potential problem with the virus entering the blood supply.

Canadian Blood Services, which manages most of Canada's supply of blood and blood products, is asking all potential donors who have traveled anywhere other than Canada, the United States or Europe to delay donating blood until one month after their return.

The agency said it is working with Health Canada and Héma-Québec to establish the length of time for delaying donations, but for now the recommendation is one month.

"The risk of Zika virus transmission from a Canadian donor to a blood recipient is very low. This deferral period is being introduced as a precaution, since to date, there has been no evidence of Zika virus transmission by transfusion causing illness in a recipient," the agency said in a statement.

The American Red Cross, the largest blood collection organization in the United States, said it is closely monitoring the virus but isn't taking a similar precaution, at least not yet.

"We are evaluating, as part of the AABB Transfusion Transmissible Disease committee, whether to ask donors to self-defer for 28 days following their return to the U.S. if they traveled to areas with ongoing Zika outbreaks," said Dr. Susan Stramer, vice president of scientific affairs at the American Red Cross.

That's likely to change if the spread of the virus becomes as bad as the WHO believes.

There is no cure for the virus and no vaccine, although there may be an experimental vaccine by the end of the year. For most of us, the threat of becoming gravely ill is mild. But we can still be carriers who can spread the disease if a mosquito bites an infected human. 

Controlling the mosquito population will be key. But the particular bug that carries the virus isn't going to make it easy:

Studies show local control is only marginally effective, since it's so hard to get to all possible breeding areas. And since Aedes aegypti has evolved to live near humans and "can replicate in flower vases and other tiny sources of water," said microbiologist Brian Foy, the mosquitoes are particularly difficult to find and eradicate.

Another prevention effort is OX513A, a genetically modified male Aedes aegypti, dubbed by critics as the "mutant mosquito" or "Robo-Frankenstein mosquito." The creation of British company Oxitec, OX513A is designed to stop the spread of Zika by passing along a gene that makes his offspring die. Since females only mate once, in theory this slows the growth of the population. Each OX513A carries a fluorescent marker, so he can be tracked by scientists.

Brazil appears to be the epicenter of the outbreak, which is very bad news. Hundreds of thousands of people from all over the world will descend on Rio de Janeiro for the Olympics later this summer. Health officials believe that this will give the virus a chance to spread worldwide by the end of the year, threatening the health of newborns and wreaking havoc with the blood supply.