Climate change futures: health, ecological and economic dimensions

262 deaths in 2003; 7,470 cases and 88 deaths in
2004. The falling death rate suggests that the virulence
of this emerging disease in North Americas is
diminishing over time.
Figure 2.8 Red-Tailed Hawk
In the summers of 2003 and 2004, cases of WNV
in the US were concentrated in Colorado and then
California, Texas and Arizona — areas that experienced
prolonged spring drought. The eastern US, with
wet springs, had relatively calm seasons. In 2005,
very variable conditions in the US were associated
with an August surge of cases scattered across
the nation, predominantly in the Southwest and
California.
Most WNV infections are without symptoms.
Approximately 20% of those infected develop a mild
illness (West Nile fever), with symptoms including
fatigue, appetite loss, nausea and vomiting, eye, head
and muscle aches. Of those with severe disease,
about two out of three can suffer from persistent fatigue
and other neurological symptoms. The most severe
type of disease affects the nervous system.
WNV has also spread to 230 species of animals,
including 138 species of birds and is carried by 37
species of mosquitoes. Not all animals fall ill from
WNV, but the list of hosts and reservoirs includes
dogs, cats, squirrels, bats, chipmunks, skunks, rabbits
and reptiles. Spread of WNV in North America follows
the flyways of migratory birds (Rappole et al.
2000). In 2002, several zoo animals died and over
15,000 horses became ill; one in three died or had
to be euthanized due to neurological illness.
Some birds of prey have died from West Nile virus.
Image: Matt Antonio/Dreamstime
The population impacts on wildlife and biodiversity
have not been adequately evaluated. The impacts of
declines in birds of prey could ripple through ecological
systems and food chains and could, in itself, contribute
to the emergence of disease. Declines in raptors,
such as owls, hawks, eagles, kestrels and marlins
could have dramatic consequences for human health.
(Some raptors have died from WNV, but the population-level
impacts are as yet unknown.) These birds
prey upon rodents and keep their numbers in check.
When rodent populations “explode” — as when
floods follow droughts, forests are clear-cut, or diseases
attack predators — their legions can become
prolific transporters of pests and pathogens. The list of
rodent-borne ills includes Lyme disease, leptospirosis
and plague, and hantaviruses and arenaviruses (Lassa
fever, Guaranito, Junin, Machupo and Sabiá), which
cause hemorrhagic fevers.
43 | INFECTIOUS AND RESPIRATORY DISEASES
The increasing domination of urban landscapes by
“generalist” birds, like crows, starlings and Canada
Geese, may have contributed to the spread of West
Nile, along with the numerous mosquito breeding
sites, like old tires and stagnant waterways.
Fortunately, vaccines for horses and some birds are
available, and newly released condors are being inoculated
to stave off their “second” extinction in the wild.
WNV has spread to the Caribbean, it is a suspect in
the decline in several bird species in Central America,
and WNV killed horses in El Salvador in 2002 and in
Mexico in 2003, the latter in clear association with
drought. Monitoring birds in northern Brazil (along
songbird flyways) and elsewhere would be warranted
in Latin America.
ECONOMIC DIMENSIONS
The costs for treatment and containment of WNV disease
in 1999 were estimated to be US $500 million
(Newcomb 2003). Subsequent health costs, screening
of blood, community surveillance, monitoring and interventions
have continued to affect life and health insurance
figures, and the costs for cities and states to maintain
surveillance and mosquito control for this urban-based
mosquito-borne disease have been substantial.
The economic consequences of large epizootics (epidemics
in animals) involving horses, birds and 300
other animals could involve direct losses in terms of
tourism and indirect losses via changes in the balances
of functional groups that help to keep pests and
pathogens in check.
CASE STUDIES