The number of holidaymakers from England, Wales and Northern Ireland who have been struck down with dengue fever has almost tripled, health officials said.
Between January and April there have been 141 "confirmed and probable cases" of the viral infection compared with just 51 during the same period last year, Public Health England (PHE) said.
Travellers have been infected while on holiday in Thailand, Sri Lanka, Brazil, Jamaica, Barbados and some other parts of Asia, Africa and the Americas.
The number of cases of the infection recorded annually is also on the increase, with a total of 223 cases reported in 2011 and 343 reported in 2012, officials said.
Dengue fever is spread by mosquito bites. Those infected suffer from severe flu-like symptoms including fever, headache and bone, muscle and joint pain.
There is no specific treatment and for most people symptoms can be managed by taking paracetamol, drinking fluids and resting. But some of those infected can develop more serious complications and need to be treated in hospital.
Experts warned travellers to take extra care around mosquitoes by applying insect repellent and wearing long-sleeved clothing at dusk and dawn when the insects are most active.
"The increase in the numbers of people returning with dengue fever is concerning so we want to remind people of the need to practise strict mosquito bite avoidance at all times to reduce their risk of becoming unwell," said Dr Jane Jones, a travel-associated infection expert at PHE.
"Of those who became unwell the majority had been to south-east Asia and the Far East, with the next highest proportions visiting the Indian subcontinent followed by the Caribbean. Anyone who develops a fever or flu-like symptoms within two weeks of returning from these areas should seek medical advice from NHS 111 or their GP."
Dr Dipti Patel, joint director of the PHE's National Travel Health Network and Centre, added: "There is no specific preventive medicine or vaccination against dengue fever and prevention relies on avoiding mosquito bites, particularly around dusk and dawn when the day biting mosquitoes are most active. To minimise the risk of being bitten, use appropriate insect repellents and wear appropriate clothing - such as long-sleeve tops and trousers to reduce the amount of skin being exposed."