Climate change futures: health, ecological and economic dimensions

44 | INFECTIOUS AND RESPIRATORY DISEASES
CASE STUDIES
THE FUTURE
CCF-I: ESCALATING IMPACTS
Warming and the intensification of the hydrologic
cycle may expose new areas and new populations to
WNV. More frequent drought and higher temperatures
might elevate baseline WNV infection rates in avian
and mammal hosts and lead to even higher levels of
viral amplification and larger epidemics. Increased
flooding might lead to wider dispersal of infected vectors
and avian hosts, putting more humans at risk. The
human health risk will also depend on the interventions,
as well as the population impacts and immunity
built up among mammalian and avian hosts. Beyond
the immediate morbidity and mortality of WNV, this
disease can lead to long-term neurological disability,
increasing the per capita loss in DALYs.
CCF-II: SURPRISE IMPACTS
The most significant non-linear threat posed by WNV
is the potential impact on wildlife, especially bird populations.
Introduction of WNV into naïve populations
in new areas, plus possible mutations to greater virulence,
could lead to the extinction of vulnerable
species. The impacts of extinction of keystone species
(that provide essential functions, such as predation and
scavenging) could ripple through ecological systems,
releasing rodents from checks on their populations. For
example, the rapid decline in vultures in India from
poisoning with toxic medications picked up from
garbage dumps (Kretsch 2003; Oaks 2003) has left
“un-recycled” carcasses along roadsides. The dog
populations filling in the niche are spreading rabies.
More flaviviruses, like Usutu, which recently appeared
in Europe, could emerge in the coming years. A rash
of illnesses of wildlife, especially mammals and birds,
could have devastating impacts on predator/prey relationships
and natural food webs.
The impact measured in DALYs would be quite substantial
if West Nile virus spreads. Naïve populations
of humans and wildlife in Latin America are particularly
vulnerable. While the resources to control this disease
exist in developed nations, large-scale outbreaks
would tax public health infrastructures in developed
and developing nations.
SPECIFIC
RECOMMENDATIONS
Surveillance and response plans are the first steps in
the control of infectious diseases. Early warning systems,
with climate forecasting and detection of virus in
birds and mosquitoes, can help municipalities develop
timely, environmentally friendly interventions.
Such measures include larvaciding of urban drains,
particularly with the bacterial agent Bacillus sphaericus
that is toxic for the culex larvae but innocuous for large
animals and humans. The alternative is methaprine, a
hormone-mimicking chemical that can enter water supplies
and possibly cause harm to marine organisms.
“Source reduction” of breeding sites is key, including
turning over discarded tires and cleaning drains, vases
and backyard swimming pools. There are numerous
means of individual protection against mosquito bites
and vaccination can be protective for horses and perhaps
some zoo animals.
Early interventions can limit the measures of last resort:
the spraying of pesticides that may harm humans and
wildlife. Street-by-street spraying is not very effective
and aerial spraying is not innocuous, although
pyrethrin agents (derivatives of chrysanthemum extracts)
are much less toxic to humans than is malathion (which
was previously used and is known to be harmful to
birds and pollinating bees).
Above all, cities need plans, monitoring systems and
communication methods to collect and disseminate
information in a timely, well-organized fashion.