WASHINGTON (Reuters) - Two U.S. soldiers serving in South America contracted Zika but have fully recovered and returned to duty, while a third, pregnant service member left the region early for fear of contracting the virus, a top U.S. commander said on Thursday.

Zika infections have been linked to thousands of birth defects as the mosquito-borne virus spreads rapidly in Brazil and other countries in Latin America and the Caribbean.

Two U.S. servicemembers stationed in Brazil and Colombia, both men, were confirmed to have contracted Zika, said Navy Admiral Kurt Tidd, commander of U.S. Southern Command.

"Both cases were confirmed. The cases have (been) resolved," Tidd said in a news briefing. "They both returned to duty."

A third, pregnant service member in the region sped up her scheduled return to the United States as a result of the Zika scare, Tidd said.

The U.S. military has discussed mosquito eradication with partner militaries in the region and has provided small amounts of supplies, including mosquito netting, Tidd said.

Much remains unknown about Zika, including whether the virus actually causes microcephaly in babies, a condition defined by unusually small heads that can result in developmental problems.

On March 9, Brazil said confirmed microcephaly cases rose to 745 and considers most of them to be related to Zika infections in the mothers. Brazil is investigating an additional 4,231 suspected cases of microcephaly.

Traces of Zika virus have been found in the bodily fluids and tissue of mothers and babies affected by microcephaly.

(Reporting by Yeganeh Torbati; Editing by Bernard Orr)