The World Health Organization says it is changing its Zika virus advice, telling travelers that anyone who has visited a place experiencing an outbreak should practice safe sex or abstinence for six months. The United Nations health agency released the new guideline Tuesday, revising guidance from June that advised men to practice safe sex or abstain for eight weeks after a trip to a Zika-infected location. The revision comes as more emerging evidence shows how Zika, a mosquito-borne virus, can be transmitted from person to person. A strain found in Latin American countries has been linked to birth defects in babies born to Zika-infected pregnant women. Also a paper written by scholars at Washington University St. Louis says they have found genetic fragments of Zika in the tears of infected mice, increasing concerns that there are still undiscovered ways for humans to contract the virus. The researchers say their findings raise the possibility that human tears could carry the virus, but caution that they have not yet undertaken research to figure out whether their findings on mice are also applicable to humans. The paper is published in the journal Cell Reports.