Emphasizing the 2016 Rio Summer Olympics set to open August 5 isn't too big to fail, 150 prominent doctors and professors are urging the games be postponed or moved to prevent the current Zika virus epidemic from spreading even further worldwide.

The concerned experts made the urgent appeal in a letter to World Health Organization (WHO) Director General Margaret Chan in which they argued the Zika virus has "more serious medical consequences than previously known." Despite well publicized efforts to contain it, the Zika virus epidemic has worsened in Rio de Janeiro, site of the Olympic Games.

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"It is unethical to run the risk," the authors said in their letter. "It is therefore imperative that WHO conduct a fresh, evidence-based assessment of Zika and the Games, and its recommendations for travelers."

The authors pointed out that despite increased efforts to wipe out the mosquitoes that spread Zika, infections in Rio have increased rather than decreased.

"Our greater concern is for global health. The Brazilian strain of Zika virus harms health in ways that science has not observed before."

"We make this call despite the widespread fatalism that the Rio 2016 Games are inevitable or 'too big to fail,' " the writers said.

Health experts worldwide have warned that having some 500,000 people travel to Brazil for the Olympics will inevitably lead to the births of more brain-damaged babies and hasten the virus' global spread.

WHO made no immediate comment on the letter. The International Olympic Committee that runs the Olympics said it doesn't intend to cancel or postpone the Games. Some 500,000 people are expected to travel to Brazil from around the world for the Olympics.

Last February, WHO declared the Zika virus outbreak a Public Health Emergency of International Concern as evidence grew the mosquito-borne Zika virus can cause birth defects and neurological problems.

The Zika virus causes "microcephaly," a rare birth defect in which babies develop abnormally small heads and brains and other neurological problems.  The virus can be transmitted from an infected pregnant woman to her fetus, where it causes microcephaly and other severe brain anomalies in the unborn child.

Pregnant women with Zika have a 13 percent risk of having baby with microcephaly. Zika also seems to be causing eye problems in babies.

The primary way pregnant women get the Zika virus is through the bite of an infected Aedes Aegypti mosquito, the same mosquito that carries dengue fever. Zika virus can be spread by a man to his sex partners. In adults, Zika can result in Guillain-Barré syndrome.

The current Zika virus epidemic began in early 2015 in Brazil then spread to other parts of South and North America.

The U.S Centers for Disease Control and Prevention (CDC) last January 15 issued a travel warning advising pregnant women to consider postponing travel to Brazil. CDC cited the "growing evidence of a link between Zika and microcephaly."

Other countries covered by the warning are Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela and the Commonwealth of Puerto Rico.

CDC director Dr. Tom Frieden is, however, against canceling or postponing the games.

"There is no public health reason to cancel or delay the Olympics," said Dr. Frieden.

Tags2016 Rio Summer Olympics, Zika virus epidemic, Rio de Janeiro, World Health Organization, microcephaly, Aedes Aegypti mosquito