On Feb. 2, the American Red Cross asked potential blood donors to wait 28 days before donating blood after visiting Zika outbreak zones including Mexico, South or Central America and the Caribbean. But the organization said the risk of Zika virus transmission via blood donations is "extremely" low in mainland U.S.

The American Red Cross also requested previous blood donors who developed Zika-like symptoms within two weeks of the donation to alert the organization so the blood can be isolated. Cases of microcephaly, a neurological disorder that causes newborns to have abnormally small head size, have been linked to the Zika virus.

The virus was also associated to Guillian-Barre syndrome, a severe autoimmune disorder that causes paralysis. Over 30 countries and territories have also reported cases of Guillian-Barre syndrome.

The first documented case of Zika infection in mainland U.S. was reported on Feb. 2 in Dallas, Texas. The state has observed seven other cases of Zika virus all linked to international travel.

Health officials said the virus was most likely transmitted via sexual intercourse instead of a bite from the Zika virus-carrying Aedes aegypti mosquito. The U.S. Centers for Disease Control and Prevention's (CDC) principal deputy director Anne Schuchat said the Dallas case was the first Zika infection that involved a non-traveler.

"We don't believe this was spread through mosquito bites, but we do believe it was spread through a sexual contact," said Schuchat.

While there is currently no blood test for Zika virus infection, Red Cross microbiologist Susan Stramer said symptoms can resemble that of a flu - fever and aches. Approximately 80 percent of infected individuals are asymptomatic. On Feb. 1, the World Health Organization declared the Zika virus and its alleged birth defects a global public health emergency.

With the increasing cases of microcephaly in Brazil, the CDC also urged pregnant women to delay travel plans to Zika outbreak zones and to get screened if they recently traveled to the said areas.

With the Rio 2016 Summer Olympics set on Aug. 5 to 21, Brazil, which is one of the countries hardest hit by the both Zika and microcephaly cases, is stepping up their precautions and daily inspections of all Olympics and Paralympics sites. Officials said the games will coincide with Brazil's dry season, which means the mosquito population will be smaller.

Photo: Canadian Blood Services | Flickr

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