The human ecology of climate change - Climate Change: Biological and Human Aspects - page 408

was severely hit, with its population declining by 47% since the arrival of West Nile
virus and by 2005 only two of the seven species had recovered to pre-West Nile
outbreak levels: blue jay and house wren.
That West Nile virus hit the headlines in North America and Europe at the beginning
of the 21st century suggests that flavivirus zoonoses (virus diseases of animals that
affect humans) have only recently presented a serious health impact on humans.
However, Japanese encephalitis (found in Asia) is a virtually identical bird-borne
disease caused by a related virus. It affects more than 50 000 people a year in Asia,
and kills 15 000 of them. It currently has a far greater health impact, but is not of
such concern in North America or Europe because it has not touched the western
hemisphere (yet). But there are occasional incidents. For example, one such illness
has already appeared in Britain, louping-ill fever. It affects a variety of animals and in
sheep is known as ovine encephalomyelitis or infectious encephalomyelitis of sheep,
for which the main vector is the sheep tick Ixodes ricinus . Other tick vectors include
Rhipicephalus appendiculatus , Ixodes persulcatus and Haemaphysalis anatolicum .
Infection has been demonstrated in other domestic species and wildlife; namely,
cattle, horses, pigs, dogs and deer, as well as in a range of species of small mammals
such as shrews, wood mice, voles and hares, the latter being considered an important
reservoir species for the virus. It can decimate grouse populations but humans are only
a tangential host and there have only been occasional isolated outbreaks of non-fatal
meningo-encephalitis. Louping-ill is endemic in rough upland areas in Scotland,
northern England, Wales and Ireland. A disease of sheep very closely related to
louping-ill has been reported in Bulgaria, Turkey, the Basque region in Spain and
Norway.
The aforementioned are just some of the diseases with an incidence in part related
to climate change. Of course, these diseases would still be with us without climate
change and in one sense virtually all diseases are in some way or other influenced by
climate and/or weather. Even common influenza viruses tend to have an annual cycle.
As a very broad generality within the range of environments commonly colonised by
humans, microbial organisms prefer warm, moist conditions as opposed to dry, cold
conditions. Consequently, as global warming will result in an increase in precipitation
globally, and as (again a generality) temperate-zone winters will become less cold, the
balance is such that a warmer world is likely to see more, rather than less, microbially
caused disease. This increased likelihood is synergistically increased by non-climate
factors such as the increasing global population and international mobility. Indeed,
this last is causing a noticeable increase in tropical infections among travellers from
temperate, developed nations returning home.
Leaving aside the above spatially leptokurtic 3 outbreaks, the early signs that global
warming is causing a change in a disease's range will be found at nations on the
edge of their range. Italy, mentioned earlier in this section, is one such critical area.

3

A probability distribution with a tail that has a kink in it at the end is known as leptokurtic. The relevance
here is that normally tropical disease cases will be found in the tropics with low to zero probability
outside of the tropics. Yet air travellers may take a disease (or their vectors) outside the tropics, causing
a small outbreak of the disease outside of the (tropical) zone of main probability. This results in a
leptokurtic distribution.