Travellers have been warned to take extra precautions against insect bites while abroad following a sharp rise in the incidence of dengue fever reported in England, Wales and Northern Ireland.
Confirmed and probable cases in the first four months of the year were nearly triple those of the same period last year, while last year's annual total was more than 50% up on 2011.
There is no specific medication or vaccination against dengue fever so public health experts say travellers should use insect repellent and wear appropriate clothing such as long-sleeved tops and trousers to deter mosquitoes, particularly at dawn and dusk.
The fever is transmitted by mosquito bites and is common in tropical and subtropical parts of the world, affecting around 100 countries, says Public Health England (PHE). Symptoms are typically a severe flu-like illness with severe headache, muscle pain and a rash. It cannot be spread from person-to-person and is rarely fatal.
In most people, symptoms can be managed by taking paracetamol, drinking plenty of fluids, and resting.
A "very small number" of people can go on to develop more serious symptoms and need to be admitted to hospital.
To the end of April 2013, 141 confirmed and probable cases of dengue fever were reported. There were 51 cases during the same period in 2012. In 2011, the annual number of cases was 223 with 343 reported last year.
In a statement, PHE said that of this year's cases 37 had reported travel to Thailand, compared with 16 for the same period in 2012. The annual totals of cases among those reporting travel to Thailand also increased year-on-year with 21 in 2011 and 58 in 2012.
Among other travel destinations reported so far in 2013, 13 had been to Sri Lanka, 11 to Barbados, nine to Brazil and six to Jamaica. Other sporadic cases had been acquired from travel to Asia, Africa and the Americas.
Jane Jones, an expert in travel-associated infections at PHE, said: "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.
"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."