Democratic U.S. Sen. Jeanne Shaheen speaks to reporters outside the federal courthouse Wednesday March 30, 2016 in Concord, N.H., about the need to hold hearings on President Barack Obama's Supreme Court nominee Merrick Garland. (AP Photo/Jim Cole)
Democratic U.S. Sen. Jeanne Shaheen speaks to reporters outside the federal courthouse Wednesday March 30, 2016 in Concord, N.H., about the need to hold hearings on President Barack Obama's Supreme Court nominee Merrick Garland. (AP Photo/Jim Cole) Credit: Jim Cole

As 10,000 athletes and hundreds of thousands of spectators from around the world prepare to descend on Brazil for the Summer Olympics, U.S. Sen. Jeanne Shaheen is raising concerns that the games could “greatly accelerate” a global outbreak of the Zika virus.

In a letter Tuesday, Shaheen called on the World Health Organization to commission and publish an evaluation of public health risks associated with the games being held in the South American country hit hardest by the virus.

“The WHO has been a tremendous leader so far in the response to the Zika virus,” Shaheen wrote in a letter addressed to WHO Director-General Dr. Margaret Chan. “But all of the efforts underway to prevent Zika are at risk of being undone if the Olympic Games spurs a global outbreak.”

Since 2015, Shaheen said, nearly 2 million Brazilians have contracted the Zika virus, which is spread mostly through mosquito bites but can also be sexually transmitted. The Summer Olympics begin Aug. 5 in Rio De Janerio and are expected to draw an estimated 500,000 spectators. Recently, public health officials have made calls for the games to be postponed or moved.

Chan said Tuesday the WHO is increasingly concerned about the Zika virus but does not recommend canceling or postponing the Summer Olympics, according to the Associated Press. Chan is going to the Olympics herself and said the health agency recommends athletes and travelers to take precautions to avoid being bitten by mosquitoes.

The virus has been shown to cause severe birth defects in newborns, including microcephaly, which causes babies to be born with abnormally small heads and brains. More than 1,110 cases of microcephaly have been confirmed in Brazil since October, according to the country’s health ministry.

The Zika virus has spread to almost 60 countries, including the United States. The U.S. Senate on Tuesday voted to advance a $1.1 billion measure to fight the Zika virus, roughly three months after the White House called for action.

New Hampshire public health officials have started to craft a Zika response plan focused on education and prevention. As of last month, the state had confirmed three cases of Zika, and it was testing 149 more people who had traveled to affected areas.

At least one athlete going to the Summer Olympics is from New Hampshire, according to the Team USA website. Sarah True of Hanover is set to compete in the triathlon.

(Allie Morris can be reached at 369-3307 or at amorris@cmonitor.com.)