MIAMI • United States health officials have reported the first known case of a man who acquired the Zika virus while travelling, showed no symptoms and infected a female partner during unprotected sex.
The case suggests that the risk of Zika's spread may be far greater than previously understood, and may lead to more stringent recommendations about who should practise protected sex and for how long after travelling to Zika-affected areas, said the US Centres for Disease Control and Prevention (CDC).
The man, who lives in Maryland, travelled to the Dominican Republic earlier this year and returned without reporting any symptoms of Zika, which can include rash, joint pain, fever and red eyes.
He had condomless sex with a female partner on two occasions, 10 and 14 days after his return. On the 16th day after his return, the woman developed a fever and rash.
In June, Maryland health authorities were notified of the case, and the woman tested positive for Zika.
She reported no other sex partners in the two weeks before her infection arose, and no blood transfusions or organ transplants.
The man was tested 29 days after his return, and the results confirmed "a recent, unspecified flavivirus infection", said the CDC, referring to a family of viruses which includes Zika, dengue and West Nile. "Semen collected on day 31 had no detectable Zika virus."
However, the man said that his only symptom had been feeling a bit tired, which he attributed to having recently travelled.
Zika is primarily a mosquito- borne virus that causes no symptoms in four out of five of those affected.
But if pregnant women are infected, they face a higher risk of having a baby with head and brain defects, a condition known as microcephaly.
In this case, the female partner was not pregnant, the CDC said.
Currently, the CDC urges couples who want to become pregnant to wait at least eight weeks if one of the partners has travelled to an area with active Zika virus transmission but did not develop symptoms.
But now, the "findings in this report indicate that it might be appropriate to consider" anyone who has unprotected sex with a person returning from an area with ongoing Zika virus transmission "as exposed to Zika virus, regardless of whether the returning traveller reports symptoms of Zika virus infection", it said.
The US Food and Drug Administration (FDA) has recommended that all blood donated in the US and its territories be tested for Zika.
Given the frequency of travel of individuals within the US, Mr Peter Marks, director of the FDA's Centre for Biologics Evaluation and Research, said there was a risk that people without symptoms of Zika could donate blood and transmit the virus.
In Hong Kong, a woman who was believed to be the city's first Zika patient tested negative for the virus on Friday and was discharged from hospital, the government said in a statement.
On Thursday, the 38-year-old woman, who had returned to Hong Kong after spending two weeks in in the Caribbean, had tested positive. She was admitted to hospital suffering from joint pain and red eyes.
The statement issued late on Friday said laboratory testing of the patient's blood and urine showed negative results for the virus. It did not explain the discrepancy with the earlier test.
AGENCE FRANCE-PRESSE, REUTERS