UK men urged to wear condoms after travel to Zika-hit countries
Men in the UK are being urged to wear condoms for a month after returning from any of the 23 countries affected by Zika.
In guidance to health professionals, Public Health England (PHE) said the risk of transmission of the virus through sex was very low but condoms should be used as a precaution.
It said: " Sexual transmission of Zika virus has been recorded in a limited number of cases, and the risk of sexual transmission of Zika virus is thought to be very low.
"However, if a female partner is at risk of getting pregnant, or is already pregnant, condom use is advised for a male traveller."
It said men should wear condoms for 28 days after "return from a Zika transmission area" if they experience no symptoms of unexplained fever and rash.
But condoms should be used for six months "following recovery if a clinical illness compatible with Zika virus infection or laboratory confirmed Zika virus infection" has been reported.
PHE added: "This is a precaution and may be revised as more information becomes available."
The body also stressed that the type of mosquito thought to be carrying Zika - Aedes aegypti - was not present in the UK and was unlikely to establish itself due to the UK's low temperatures.
US officials have ruled out a vaccine to protect against Zika in the next few years as concerns continue to mount about the spread of the virus.
The World Health Organisation (WHO) announced on Thursday that Zika was "spreading explosively" throughout the Americas and "the level of alarm is extremely high".
The WHO has set up an International Health Regulations Emergency Committee to examine Zika and will meet on Monday to decide whether it constitutes a global emergency. The last time a global emergency was declared was for the Ebola virus.
Zika has been linked to thousands of babies being born with underdeveloped brains in Brazil.
Colombia has also seen a rise in the number of patients diagnosed with a rare neurological disorder which can cause paralysis.
The US has said it has two potential candidates for a vaccine for the Zika virus. While clinical trials may be able to begin before the end of this year, there will not be a widely available vaccine for several years.
In Colombia, health minister Alejandro Gaviria has reported a " substantial increase" in the number of people with Zika reported to have Guillain-Barre syndrome, which is rare in the UK.
It is a serious condition of the peripheral nervous system and m ost people (around 60%) develop it after having a viral or bacterial infection.
Experts believe the infection may trigger the immune system to attack nerve roots and peripheral nerves.
The WHO predicts three to four million people will be infected with Zika in the Americas this year.
In a briefing to the WHO's executive board on Thursday, WHO director-general Margaret Chan said the organisation was "deeply concerned".
She said : "Arrival of the virus in some places has been associated with a steep increase in the birth of babies with abnormally small heads and in cases of Guillain-Barre syndrome.
"A causal relationship between Zika virus infection and birth malformations and neurological syndromes has not yet been established, but is strongly suspected.
"The possible links, only recently suspected, have rapidly changed the risk profile of Zika, from a mild threat to one of alarming proportions."
In the UK, PHE and the National Travel Health Network and Centre (NaTHNaC) issued updated advice for pregnant women on Wednesday
Dr Dipti Patel, director at NaTHNaC, said: "We strongly advise all travellers to avoid mosquito bites and urge pregnant women to consider avoiding travel to areas reporting active Zika transmission.
"If travel to these areas is unavoidable, or they live in areas where Zika virus transmission is occurring, they should take scrupulous insect bite avoidance measures both during daytime and night-time hours."
Since the start of the outbreak in 2015, five UK travellers have been diagnosed with the Zika virus.
Symptoms of infection may include fever, joint pain, itching, rash, conjunctivitis or red eyes, headache, muscle pain and eye pain.