Reports are also describing the first two cases of Zika-linked microcephaly in Thailand.
Since the Zika outbreak began last year, thousands of babies, mostly in Brazil, have been born with the devastating brain defect after their mothers were infected with the mosquito-borne virus during pregnancy.
French scientists also reported a disturbing discovery on Thursday: The virus was found inside the sperm of a man who had just returned from French Guyana, and not just in his semen. It is not clear if infected sperm can transmit Zika, the researchers noted, but the finding has important implications for the prevention of sexual transmission of Zika.
It also raises questions about the need to include Zika screening in the testing of sperm donations in fertility centers, the researchers said. Most sexually transmitted diseases stick to the surface of sperm, and can be washed off during fertility procedures, they explained.
Meanwhile, the U.S. Centers for Disease Control and Prevention on Friday released new recommendations on how long men with either Zika infection or exposure should abstain from trying to conceive, lengthening the waiting period from eight weeks to six months.
CDC officials did offer up a bit of good news: Children and teens who are infected with Zika typically suffer only mild illness, as most adults do.
Both reports were published in the Sept. 30 issue of the CDC's Morbidity and Mortality Weekly Report.
In the French report on Zika infecting sperm, scientists from INSERM (the French equivalent of the U.S. National Institutes of Health) and Toulouse University took blood, urine and semen samples from a 32-year-old man who was showing signs of Zika infection.
The investigators found evidence of the virus in all of the samples for roughly a month after infection. But the virus persisted in the semen for a little over four months. When they examined semen samples under a microscope, they found Zika was present in 3.5 percent of the man's sperm.
Similar results were seen in two other patients, with the virus persisting in all samples for a little over two months and in semen samples for a little under four months, the study authors reported.
The findings were published online Sept. 29 in The Lancet Infectious Diseases.
In the CDC travel advisory, the 11 Southeast Asian countries involved were Brunei, Cambodia, East Timor, Indonesia, Laos, Malaysia, the Maldives, Myanmar, the Philippines, Thailand and Vietnam.
The U.S. Centers for Disease Control and Prevention provides more information on mosquito-borne diseases.
This Q & A will tell you what you need to know about Zika.
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