One little bite from a tiger mosquito or a tick can have fatal consequences: malaria, dengue and yellow fevers, chikungunya and Lyme disease can all be contracted this way. Experts speak of so-called vector-borne disease - every year, they infect more than a billion people.

Although vector-borne diseases are found mainly in the tropics and subtropics, they are being observed more often in temperate climates. The WHO currently estimates 77,000 cases occur annually in Europe.

The majority of vector-borne diseases in Europe are brought in by those who were abroad. "The free movement of people and goods has also allowed the free movement of vectors," said Raman Velayudham of the WHO's neglected tropical diseases department. "People are the main carriers of the virus - we carry it from place to place, making it available to mosquitos," Velayudham told DW.

Poor most affected

But Velayudham reminds that developments in Europe shouldn't distract from the fact that countries of the Global South are shouldering the greatest burden from vector-borne diseases. "The world's poorer populations are most affected," he warned.

More than a million people die every year from diseases such as malaria, dengue fever, Chagas disease or Japanese encephalitis - often small children, who aren't as resistant to such infectious agents.

Vaccines are available or being developed for some of the diseases, for instance Lyme disease, which is transmitted via ticks. Medicines also exist to treat many of these illnesses, but this only alleviates the symptoms, which include fever, chills, pain, sores, and inflammation of brain and nerve membranes. The majority of those afflicted, however, go without any treatment at all.

Dengue coming

Among vector-borne diseases, dengue fever appears to be spreading around the globe faster than others. The WHO and the International Federation of Red Cross and Red Crescent Societies (IFRC) have warned of the effects from this viral infection, which they describe as a "silent danger."

Around 50 years ago, dengue only occurred in nine countries. Now, the mosquito-borne illness is present in more than 100 countries, making 40 percent of the world population at risk of catching it. Each year, 50 to 100 million people are newly infected with the sickness, which can cause fever, severe muscle and joint pain, and headache. A small percentage of infections can develop into the severe and fatal dengue hemorrhagic fever.

"It's not necessarily the number of deaths we're highlighting, it's more the costs of dengue," said Amanda McClelland of the IFRC. "Families living at the edge of poverty can't afford to get this illness," she added.

And dengue is srpeading quickly. According to WHO estimates, between 100 and 380 million people are infected worldwide. After malaria, dengue has become the second-most-common fever illness brought back by Europeans traveling abroad. In Germany alone, there are 500 cases per year.

The Aedes mosquito, which transmits dengue as well as yellow fever and chikungunya, could also spread in Europe as the climate warms. Since 2010, local cases have been recorded in Portugal, southern France and Croatia.

It's really quite simple

On World Health Day, the WHO is calling for better protection against vector-borne disease. Velayudham points out that simple personal protective measures can go a long way. "Insecticide-permeated bed nets help against malaria, while dengue can be kept at bay with mosquito repellent and screens over windows," he said.

But individual measures won't release governments from their responsibility to control the outbreak of vector-borne diseases. Health organizations need to observe and fight invasive organisms, and monitor the epidemiology of vulnerable populations to prevent and properly respond to outbreaks.

The WHO's message on World Health Day is clear: Vector-borne diseases are preventable. "No one should die from a mosquito, sandfly or tick bite in the 21st century."