Globalisation has a bigger part to play than climate change in the emergence of infectious diseases transmitted by insects in Europe, according to a set of reports published this month in Eurosurveillance.

 

In the last decade, almost a third of all incidences of emerging infectious disease were caused by vector-borne pathogens, explain¹ Guy Hendrikx and Renaud Lancelot in an editorial that accompanies the reports. Concerns over emerging infectious diseases prompted European health authorities in 2009 to establish VBORNET, a Europe-wide network for arthropod surveillance for public health. The infectious diseases designated a priority for Europe by this group are transmitted by arthropods including mosquitoes, ticks and sandflies. This month’s reports highlight findings of reviews and risk assessments carried out by members of the group.

 

The reviews look at the risk of diseases transmitted by mosquitoes, including dengue fever, yellow fever, West Nile fever, as well as diseases spread by sandflies, such as leishmaniasis. The authors looked at evidence for the current distribution of each disease worldwide, and for factors that could prompt the arrival of these diseases to new areas. Finally, they examined whether outbreaks could be sustained in European countries.

 

For the diseases transmitted by mosquitoes, globalisation is likely to play a bigger role in their emergence in Europe compared with climate change, says Paul Reiter from the Pasteur Institute in Paris, France. He looked at three viruses transmitted by mosquitoes in two separate reviews.

 

One of these, West Nile virus, is already present in some parts of Europe, he explains². If this virus, or others that are not already widespread, became established across Europe it would pose a “serious danger” to public health.

 

West Nile fever is one to watch, he explains, as the arrival of the virus in New York in 1999 led to “spectacular and unprecedented” spread of the disease on the continent. Over the 10 years that followed the virus established itself across the Americas, and can now be found anywhere from Canada to Venezuela. It has caused almost 30,000 cases of illness and more than 1400 deaths so far.

 

But Reiter points out that less than 200 people have died of West Nile fever in Europe over the past decade. An increasing number of small outbreaks of West Nile fever have been occurring in Europe, mainly among horses, he explains. Although mammals prove to be a ‘dead end’ for transmission of the virus, similar numbers of horses and people have been affected over the past decade in the Americas. But this may be down to increased awareness of the virus as well as better surveillance and diagnostic facilities.

Given that West Nile fever is relatively rare in Europe, it is difficult to assess what part climate plays in the transmission of the pathogen, according to Reiter.

 

For the flaviviruses that cause dengue and yellow fever, history suggests that conditions needed for their transmission are present in the temperate regions of Europe, Reiter says³ in the second review. This means that these diseases could take hold on the continent. One of the two mosquito species capable of carrying the viruses, Aedes albopictus, was introduced into Europe in the 1970s and is now established in 12 countries in the southern part of the continent. Scientists predict that the mosquito is likely to spread northwards in the future.

 

Reiter says the movement of Ae. Albopictus to new areas is down to globalisation, as research suggests the mosquitoes likely arrived in the USA through the tyre trade.

 

Although Ae. albopictus is believed to be the least important vector of dengue and yellow fever viruses, epidemics of dengue fever have occurred in areas where this is the only mosquito capable of spreading the disease, according to Reiter. This species can also transmit the chikungunya virus, and an outbreak of this disease in Italy three years ago proves that the mosquito can spark epidemics in Europe. The virus was imported into the area by a traveller returning from the Indian subcontinent, resulting in more than 200 people becoming infected. This adds strength to the idea that human movements can drive disease emergence, says Reiter.

 

Dengue fever is already the second most common cause of hospitalisations for European travellers when they return from travel to the tropics. Travellers infected with the virus on returning to parts of Europe that harbour Ae. albopictus could spark an outbreak of the disease. Rieter adds that epidemics of dengue fever in areas that have not seen the virus before are often “explosive”.

 

“In short, globalisation is potentially a far greater challenge to public health in Europe than any future changes in climate,” he writes in the West Nile virus review.

 

Dog travel could also contribute to the emergence of infectious diseases in Europe, writes⁴ Paul Ready in a review of the risk of leishmaniasis spreading on the continent. Some countries in the Mediterranean belt are endemic for Leishmania infantum, one species of the parasite that causes the disease, which is spread by sandflies. Domestic dogs are the reservoir for the parasite in these areas.

 

“Increasing dog travel poses a significant risk of introduction of L. infantum into northern Europe from the Mediterranean region,” writes Ready. He adds that previously unaffected northern areas of Italy have become endemic for the disease in recent years.