RUMS Review Vol. VIII Issue I - January 2023

“Climate change will
principally increase
the incidence of
zoonotic epidemics"
Zoonotic viruses are viral
pathogens that jump from animal
hosts to the human population.
They often result in recurrent
outbreaks that leave morbidity
and mortality in their wake. One
such virus is the Zaire ebolavirus.
The widely publicised Zaire
ebolavirus outbreak of 2014
began in remote villages in
Central Africa and went on to
infect 11 countries in Africa,
Europe and North America and kill
over 11 thousand people. We now
know that the virus entered the
human population via a single
crossover event with a fruit bat.
Knowing that the innocuity of one
fruit bat crossover event could
deteriorate into an epidemic
illustrates the havoc these
pervasive pathogens could
potentially wreak if given the
opportunity. Regrettably, climate
change appears to be that exact
opportunity. Climate change will
principally increase the incidence
of zoonotic epidemics by altering
weather patterns and the
behaviours of zoonotic animal
reservoirs.
Provided that shifts in animal
behaviour keep pace with
changes in the climate, the
majority of mammals will be
exposed to previously unfamilar
species, representing a doubling
of potential species contact.
This phenomenon, most
prominent in tropical Africa and
Southeast Asia, will increase the
probability of zoonotic spillover
across populations. Through
climate data, this has already
been observed.
As a nation with a high northward
latitude, climate changes have
been more pronounced and thus
more easily discerned in Sweden.
In 2021, the Swedish University
of Agricultural Sciences
investigated the seroprevalence
of endemic Puumala
Orthohantavirus (PUUV) and the
population density of their animal
reservoir - bank voles - between
1980-89 and 2000-2003. While
the population density of bank
voles was the same in both
periods, the seroprevalence of
PUUV was significantly higher
during the 2000-2003 period.
The main independent variables
were the significantly higher
November temperatures in 2000,
and the wetter, earlier winters
engendered by climate change. It
is worth noting that the increase
in seroprevalence of PUUV likely
translated to an increased risk of
human infection.
This perfectly illustrates the
tangible mechanism in which
climate change modifies our
ecosystems and also combats the
misconception that zoonoses are
exclusive to the southern
hemisphere.
Whilst climate change will
increase the frequency of
endemic zoonotic outbreaks,
novel, zoonotic epidemics could
become more prevalent due to a
dangerous reservoir host— bats.
Bats have been disproportionately
responsible for novel viral
sharing events due to their lack
of dispersal constraints. Most
reservoir hosts have constraints -
namely an inability to migrate to
newly-suitable locations - that
prevent them from spreading
zoonoses to new countries and
continents. However, bats
overcome this constraint through
flight, unfettered migration and
their relatively long life spans.
This allows them access to
previously uninhabitable domains
rendered habitable by increasing
temperatures.
This raises concern as bats are
known reservoirs of several
viruses, including the Ebola virus,
Nipah virus, and Lyssavirus
amongst others. Therefore, if
rising temperatures continue to
expand their habitats, we risk
making millions more people
susceptible to novel viral
infections, for which health
infrastructures may be
unprepared.
It is clear that if we continue
down this path of high carbon
emissions and inaction, we
needlessly endanger ourselves to
these often debilitating and fatal
pathogens. Moreover, we risk
diverting billions of pounds worth
of funds and resources from
worthwhile endeavours to
overcome this self-erected
hurdle. Whilst I appreciate that
the conclusions drawn might
appear exaggerated, even
hyperbolic; an increased
frequency, novelty and severity
of viral zoonoses is a future that
we may genuinely have to face in
our lifetimes.
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