Spanish health authorities have confirmed a case of a man spreading dengue through sex, a world first for a virus which until recently was thought to be transmitted only by mosquitos.
The case concerns a 41-year-old man from Madrid who contracted dengue after having sex with his male partner who picked up the virus from a mosquito bite during a trip to Cuba, said Susana Jimenez of the Madrid region's public health department.
His dengue infection was confirmed in September and it puzzled doctors because he had not travelled to a country where the disease, which causes severe flu-like symptoms such as high fever and body aches, is common, she added.
"His partner presented the same symptoms as him but lighter around ten days earlier, and he had previously visited Cuba and the Dominican Republic," she said.
"An analysis of their sperm was carried out and it revealed that not only did they have dengue but that it was exactly the same virus which circulates in Cuba."
A "likely' case of sexual transmission of dengue between a man and a woman was the subject of a recent scientific article in South Korea, she said.
In an e-mail sent to AFP, the Stockholm-based European Centre for Disease Prevention and Control (ECDC), which monitors health and disease in Europe, said this was "to our knowledge, the first sexual transmission of the dengue virus among men who have sex with men."
Dengue is transmitted mainly by the Aedes Aegypti mosquito, which thrives in densely-populated tropical climates and breeds in stagnant pools of water. It kills 10,000 people a year and infects over 100 million.
The disease is fatal only in extreme cases but the symptoms are extremely unpleasant, including a high fever, severe headaches and vomiting. It also exacts a heavy economic burden on countries as sufferers are unable to work, as well as overwhelming health services when there is a severe outbreak.
It is most serious - and deadly - in children, especially young girls. Scientists do not know why.
Dengue is most commonly caught by people travelling to hotter climates such as South East Asia, Africa, Australia, the Caribbean and South and Central America.
Prevention is vital, as it is the main way to control disease – there are four strains of dengue, making it difficult to develop treatment options.
There is currently no specific drug to cure dengue and Dengvaxia, the first vaccine developed, is effective only in people who have already had the disease.
Researchers announced earlier this year that they expect the disease will spread across much of the globe within the next 60 years. They say dengue, also known as "break-bone fever" because of the joint pain it causes, will threaten 60 per cent of the world's population, or six billion people, by 2080.
The greatest increase is expected to be in Africa, but much of the south eastern United States is predicted to see a rise in the disease, as is Australia, parts of southern Europe, and many larger cities in southern China and Japan.
In the 1970s the flu-like virus was endemic in just nine countries.
But now severe dengue has taken hold in more than 100 countries, with roughly half of the world’s population at risk. Incidence rates are spreading as a result of a combination of rapid, unplanned urbanisation, increasing intercontinental travel and the warming temperatures caused by climate change, experts have warned.
In July Bangladesh faced its worst dengue outbreak in history after more than 1,300 people were diagnosed in 24 hours in one hospital.
In September Nepal also announced an unprecedented outbreak.
India, to combat the threat, has agreed to trial an innovative technique which sterilises mosquitoes with radiation.
The sterile insect technique (SIT) exposes male mosquitoes to enough radiation to sterilise them. They are then released into the wild en masse to mate with females, who then do not reproduce.
Over time, it is hoped that the technique will reduce the population as fewer mosquitoes will be born.
SIT has been used successfully in parts of Africa, such as Senegal, to eradicate the tsetse fly which transmits sleeping sickness.