Three Britons have been infected with zika virus, which is linked to deformities in babies, after travelling to South and Central America, Public Health England said.
The three travellers picked up the disease through mosquito bites in Colombia, Suriname and Guyana, PHE confirmed.
Pregnant women have been warned not to travel to countries where the infection has been reported.
PHE said the virus “does not occur naturally” in the UK and said that the cases came to light on or before January 18.
The virus is transmitted through mosquito bites and “is not spread directly from person to person”, the PHE said.
“A small number of cases have occurred through sexual transmission or by transmission from mother to foetus via the placenta,” a spokesman added.
Three people in New York have also been found to be infected. They had all travelled outside the United States, to countries where the disease is spreading rapidly, the New York State Department of Health said, without specifying exactly where they had been.
Officials said that one of the people had completely recovered while the other two were still recuperating.
The virus has been linked to thousands of cases of a birth defect called microcephaly, when babies are born with abnormally small heads, which can cause brain damage.
Howard Zucker, New York State Health Commissioner, said: “We are urging resident, especially pregnant women, to check all health advisories before travelling and take preventative measures when travelling to affected countries.”
Women in the 22 identified areas of Latin America and the Caribbean were also advised to wear long sleeves and trousers and to apply insect repellent.
The disease was first discovered in Africa in the 1940s and there are currently confirmed cases in 18 states in Latin America and the Caribbean.
Typical symptoms are flu-like, with fever, joint pain, rash conjunctivitis, headache and muscle pain all reported. Some people display no signs of infection at all.
The virus causes a short illness in most people, lasting between two and seven days, and causes death only in rare cases.