Select Committee on Innovation, Universities, Science and Skills Written Evidence

Memorandum 39

Supplementary submission from the Institute for Animal Health



  The Intergovernmental Panel on climate-change (IPCC) has predicted that in the early part of the 21st Century temperatures will increase, by up to 6.2oC and that maximum warming will occur at higher latitudes and during the winter, and that night time temperatures will increase more than day time. It is also predicted that precipitation (rainfall) patterns will change and that there will be an increase in extreme weather events. Current climatic changes seem to be in line with these predictions.

  Some vector-borne (ie insect-borne) diseases are likely to be among those most strongly affected by such changes because insect vectors:

    —  Are poikilothermic (cold-blooded) and therefore respond directly and quickly to changes in temperature.

    —  Are small and easily desiccated, therefore dying rapidly if humidity decreases, but survive for longer periods if the humidity increases.

    —  Breed in aquatic environments so will have more breeding sites if rainfall increases and less if it decreases.

    —  Are highly mobile and so can move quickly on the wind, over large distances. If climate-change brings more extreme weather events eg increased windiness, this is likely to increase the dispersion of such vectors.

    —  Are most active at night rather than during the day

  Consequently, climate-change is likely to have profound effects upon many insect-borne diseases. Temperature increases are probably the most important change and may have the following effects:—

For the insect vector an increase in temperature may cause:

    —  An increase in metabolic rate leading to more frequent blood-feeding and hence an increase in the opportunity to transmit. Also, as blood-feeding fuels egg production, this will also cause increases in vector population size.

    —  An extension in the geographical range of some insect vectors, as most prefer warm climates, leading to an extension in the range of the pathogen.

    —  An extension in the period of vector activity over a greater proportion of the year, as winters decrease in duration and severity, thus facilitating extended pathogen transmission and easier over-wintering of the pathogen.

For the pathogen an increase in temperature may cause:

    —  An increase in the replication rate of the pathogen in the vector, leading to earlier transmission.

    —  More efficient transmission by an increased proportion of a vector population leading to an overall increase in transmission rate.

    —  Additional insect species to become vectors, leading to transmission by a wider spectrum of vectors.

  Virtually all of these changes impacting on both the vector and the pathogen have already been documented for bluetongue virus (BTV) and have led to 12 BTV incursions into Europe since 1998 when there were only 2 in the previous 40 years. Furthermore, these recent and on-going incursions have included many areas across northern Europe when previously this virus only, sporadically affected, SW Iberia and a few Greek islands. Other diseases are likely to follow where BTV has led.

May 2008

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