The Zika virus is coming to the United States and health officials should prepare for its arrival.

That was the advice delivered today by the Pan American Health Organization.

Officials at the organization said the virus is expected to spread to the U.S. relatively soon as well as every country in the Western Hemisphere where the Aedes mosquitoes that carry the disease live, according to a story posted by USA Today.

The virus has been confirmed in 21 countries now. Its spread has prompted the U.S. Centers for Disease Control and Prevention (CDC) to issue a level 2 travel alert, warning pregnant women to avoid those 21 countries.

The Zika virus has been linked to microcephaly, a condition in which babies are born with small heads and incomplete brain development. Brazil has reported 3,500 cases of this ailment since last fall. It normally sees 100 to 200 cases a year, according to USA Today.

For most adults, the Zika virus causes relatively mild symptoms such as fever, rash, and joint pain. The symptoms usually last several days to a week, according to the CDC.

Testing for Zika is difficult because there are no commercially available diagnostic tests. Blood samples must be sent to the CDC offices in Atlanta, according to USA Today.

At the moment, there is no vaccine or other treatment for Zika.

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World Health Organization Urged to Act

U.S. officials have called on the World Health Organization (WHO) to take action against the Zika virus, according to a story on the Reuters news service.

Georgetown University researchers urged WHO Director-General Margaret Chan to call an emergency meeting of health and infectious disease experts as early as next week, according to Reuters.

The meeting would focus attention on funding and research, according to their viewpoint posted today on the Journal of the American Medical Association (JAMA).

On Thursday, Chan announced she would convene a meeting on Monday of an International Health Regulations Emergency Committee.

In their editorial, the researchers called on WHO officials to heed the lessons learned from the 2015 Ebola crisis in Africa that killed more than 10,000 people.

WHO officials were harshly criticized for what critics said was a slow response to the outbreak of that deadly disease.

“A key lesson learned from that searing experience was the need for an intermediate-level response to emerging crises, thus avoiding overreaction while still galvanizing global action,” the researchers wrote.

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Why the Virus Is Spreading Rapidly

The Zika virus isn’t usually spread from person to person. It’s transmitted by bites from infected mosquitoes.

Although it isn’t certain why this particular outbreak is happening so quickly, researchers have some theories.

One is that climate change and the current El Nino weather patterns are providing more fertile breeding grounds for the mosquitoes, experts told USA Today.

The United States could be vulnerable to those mosquitoes, the experts added, because of the country’s pockets of poverty.

In poor areas, mosquito-borne diseases spread more quickly because trash such as discarded tires can create breeding grounds. In addition, poor residents may not be able to afford window screens or mosquito spraying.

The experts added that international air travel may be helping to spread the disease. There is one theory that the disease solidified itself in Brazil during the 2014 World Cup soccer championships in that country.

That has brought up new concerns for the Zika virus and this summer’s Olympic Games in Brazil.

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