Food Protection Trends - February 2009 - 92

Possible incursion (and persistence) of exotic pathogens into new areas Exotic pathogens may be released into new locations regularly through a variety of routes. These release events may not necessarily be directly related to climate, but once in a new area, climate-related changes may promote the transmission and establishment of the pathogen. Potential routes of entry to EU for exotic pathogens Potential routes of entry for an exotic pathogen include infected wildlife, livestock, pets or persons entering from a region where the disease is endemic, import of contaminated meat and meat products, and import of germplasms. In the case of vector-borne diseases, pathogens may also be released into a new region through movement of infected vectors. Migrant birds are a common, but inadequate, explanation for the introduction of ticks infected with exotic pathogens; for example randolph and Ergonul (2008) argue against birds introducing Crimean-Congo haemorrhagic fever virus (CCHFV) into Turkey. many arboviruses are transmitted by flying insects. Examples include mosquitoes and biting midges which serve as vectors for Rift Valley fever virus (RVFV) and bluetongue virus (BTV), respectively. Thus, BTVinfected Culicoides midges could be blown from mainland Europe into GB (Gloster et al. 2007). The completion of the trans-Sahara road will heighten the risk of introduction of rVFV north of the Sahara into southern Europe (reiter 2008). rVFV was detected outside Africa for the first time in the Arabian peninsula in September 2000; it is estimated that seven million animals are exported to Saudi Arabia every year from Africa during the pilgrimage seasons (reiter 2008). Global transport and movement of goods and people have increased significantly over the last 20 years, and may have underpinned the emergence of Chikungunya virus (CHIkV) in Italy for the first time (reiter 2008). The mosquito vector for this virus, Aedes albopictus, established in Southern Europe after its eggs were introduced in consignments of car tyres imported from Asia (reiter 2008). A traveller returning to Italy from India, where he had been infected, introduced CHIkV triggering a small outbreak. Air transportation of flowers from sub-Saharan Africa could be another source of introduction of BTV-infected midges into northern Europe. Factors through which climate change may affect incursion and establishment of new pathogens Climate change may affect both the range of a vector and its interaction with the pathogen. In the case of BTV, the traditional vector Culicoides imicola has extended its range northwards from Africa into southern Europe, promoting incursions of BTV serotypes 1, 2, 4, 9 and 16 (Purse et al. 2005) and also African horse sickness virus (AHSV). In northern Europe, however, midges of the C. obsoletus complex have become new vectors for the transmission of BTV, namely serotype 8 (mehlhorn et al. 2007). The higher temperatures appear to have increased the competence of the vectors to transmit the disease. Milder winters may also allow over-wintering of latently-infected midges in the case of AHSV (Mellor and Hamblin 2004). Global warming is associated with warmer nights (Beniston and Diaz 2004) which increases midge flight activity and hence livestock exposure to infected midges. Current midge-borne diseases, although causing severe disease in livestock, are not generally zoonotic. While the evidence is strong that climate change has affected midge-borne diseases of livestock, there is more controversy over the impact of climate change on tick-borne diseases (randolph 2008). There is evidence that ticks are not only expanding their range northwards in countries such as Germany and moving to higher altitudes in the Czech Republic, but also are now active through the winter months (Suss 2008) in Germany. many tick-borne diseases are zoonotic and furthermore may be transmitted to humans through contact with body fluids during butchering of infected livestock. Examples include CCHFV and an emerging flavivirus called Alkhurma haemorrhagic fever virus (AHFV) which was only discovered in 1995 in Saudi Arabia (Charrel et al. 2007). AHFV has been found in Ornithodoros savignyi ticks which are associated with camels (Charrel et al. 2007) and are widespread in the Middle East. O. sonrai is an example of a tick which has expanded in range in response to the drought in sub-Saharan Africa (Trape et al. 1996). It serves as a vector for African swine fever virus (ASFV) in Senegal. Tick-borne transmission of ASFV in southern Iberia through the tick O. erraticus promoted persistence of the disease and prolonged its eradication. Ornithodoros ticks require dry conditions and desertification through climate change could promote expansion of their range. mosquito-borne diseases include rVFV, West Nile virus (WNV), CHIkV and alphaviruses of the equine encephalitis virus group. It is important to note that climatic factors may be less important than, or interact with, other factors such as habitat change, globalised movement, farming practice and human living conditions in the transmission of some mosquitoborne diseases, for example malaria and CHIkV (reiter 2008), although martin et al. (2008) suggest that extreme weather events might create the necessary conditions for RVFV to expand its geographical range northwards and cross the Mediterranean Sea. Outbreaks of RVFV in sub-Saharan Africa are associated with prolonged drought followed by heavy rainfall which produces mosquito breeding sites (Baylis and Githeko 2006). WNV has spread rapidly across the New World after its introduction in 1999 infecting birds and horses. During the economic downturn in 2008, an increase in WNV cases in humans has been reported in California due to stagnant swimming pools which provide a mosquito breeding site. While WNV and Eastern equine encephalitis virus cannot be transmitted to humans from body fluids of horses, butchering of RVFV-infected livestock is a route of transmission to humans. Wildlife is important both as a source of disease reservoirs and as hosts for ticks. Many arboviruses require a continual source of immunologically naïve vertebrate hosts. For example, hares may play and important role in the transmission of CCHFV and social changes in Turkey between 1995 and 2001 allowed hare abundance to increase (Randolph and Ergonul 2008). The interaction between wildlife, humans and livestock is important in the emergence of new pathogens and may be affected by climate change. An example from outside the EU, although not directly related to climate change, is the emergence of Nipah virus in malaysia through encroachment of pig farming into fruit bat habitats. Transmission to humans occurs through contact with body fluids of infected pigs and via raw date palm sap (luby et al. 2006). Climate change may affect the range, abundance, movement and behaviour of wildlife. Deer and badgers are increasing in GB, perhaps aided 92 FOOD PROTECTION TRENDS | FEBRUARY 2009

Food Protection Trends - February 2009

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