The key finding of an ECDC-initiated assessment on the importance and magnitude of vector-borne diseases for Europe is that climate and environmental changes may increase the risk of vector-borne disease outbreaks in the future. Vector-borne diseases are those spread by mosquitoes, sand-flies, ticks and rodents. They include diseases such as dengue, West Nile and chikungunya fever, nephropathia epidemica and tick-borne encephalitis (TBE), which all have the potential to cause outbreaks in parts of Europe. The outbreak of chikungunya fever in the area of Ravenna, Italy, last summer is an illustration of this risk. The initial findings of the risk assessment were presented today at ECDC in Stockholm, at the end of two day meeting of experts from across Europe. The final report on the assessment will be published in the coming months.

The Director of the European Centre for Disease Prevention and Control (ECDC), Zsuzsanna Jakab, said:

“The climate and environmental changes being predicted by experts will alter the risk to Europe from vector borne diseases. We are likely to see the spread of diseases such as tick-borne encephalitis, or even chikungunya fever, to places where they have not been seen before. It’s not just environmental changes that give rise to this risk. Globalisation, and the increased travel and trade that it brings, is also quickening the pace at which diseases can spread to new areas. We need to better understand how these changes will alter the risk of vector-borne diseases, to better target surveillance and control, and improve preparedness in European countries.”

An example of how globalisation can drive the spread of vector-borne diseases is the international spread of the Aedes albopictus mosquito (also know as the Asian Tiger Mosquito), which has been linked to outbreaks of the disease chikungunya fever. This species of mosquito has spread across large parts of Asia, Africa and the Americas in recent decades. It has also spread to some parts of Europe, including most of Italy. In the summer of 2007, a traveller from India introduced chikungunya fever to the mosquitoes in the area of Ravenna, Italy, and there was an outbreak affecting nearly 250 people.

Key factors contributing to a heightened risk of vector-borne diseases

Disease vectors are extremely sensitive to environmental and climate change, in particular changes in temperature and humidity. Authoritative climate scenarios for the future predict that many parts of Europe will become hotter and wetter. These changes are likely to impact on disease vectors, such as mosquitoes transmitting West Nile fever, chikungunya fever and possibly even dengue or Rift Valley fever.

Globalisation and increasing international travel are also contributing to the spread of disease vectors as well as the diseases they transmit. It is documented that the Aedes albopictus mosquito was introduced to Europe by the used tyre industry, as the tyres provide excellent breeding sites for mosquitoes. In the summer of 2007, it took only one man infected with the chikungunya virus to trigger an outbreak after he was bitten by an Aedes albopictus mosquito on his return from Kerala, India, to a village close to Ravenna, Italy.

Human factors are also identified as important in heightening the risk of vector-borne diseases. For example, the more time that people spend in forested areas, the more they increase their chances of being exposed to diseases transmitted by ticks, such as TBE, or by rodents, such as nephropatica epidemica.

What is the public health importance of vector-borne diseases?

Every year millions of people around the world, including in Europe, are affected by vector-borne diseases, the symptoms and severity of which are variable. For example, chikungunya virus is transmitted from human to human by Aedes mosquitoes, such as the Aedes albopictus (Asian Tiger Mosquito). The virus causes sudden onset of high fever, severe joint pain, muscle pain and headache. While chikungunya fever is usually non-fatal, a small number of patients may develop serious complications or chronic conditions. A huge epidemic has been striking Africa, the Indian Ocean and India over the last 3 years, with millions of cases. The 2007 outbreak of chikungunya fever in Ravenna district, Italy was the first documented transmission of the virus on the European continent.

Similarly, humans are infected with dengue virus through the bites of Aedes mosquitoes. Dengue is endemic in most tropical countries. After an incubation of 8-10 days, many people infected with the virus develop a mild flu-like illness. A small number of these cases may develop into dengue hemorrhagic fever, which has become a leading cause of morbidity and mortality in some Asian and South American countries. The last documented dengue outbreak in Europe took place in Greece during 1927-8 (1 million cases, 1,000 deaths).

Tick-borne encephalitis (TBE) is one of the most dangerous infections of the central nervous system in Europe. TBE has become a growing public health challenge as a result of an increasing incidence in some areas of Europe where the disease is endemic, as well as an increase in its geographical distribution. The number of human cases in all endemic regions of Europe has increased by almost 400% in the last 30 years. TBE has become an international public health problem also because of increased travel to risk areas.

Further information

Link to articles published in
Eurosurveillance.

Link to Mission Report:
Chikungunya in Italy

Link to ECDC webpage on vector-borne diseases

European Centre for Disease Prevention and Control