[Marxism] In Zika Epidemic, a Warning on Climate Change
lnp3 at panix.com
Sun Feb 21 10:50:50 MST 2016
NY Times, Feb. 21 2016
In Zika Epidemic, a Warning on Climate Change
By JUSTIN GILLIS
The global public health emergency involving deformed babies emerged in
2015, the hottest year in the historical record, with an outbreak in
Brazil of a disease transmitted by heat-loving mosquitoes. Can that be a
Scientists say it will take them years to figure that out, and pointed
to other factors that may have played a larger role in starting the
crisis. But these same experts added that the Zika epidemic, as well as
the related spread of a disease called dengue that is sickening as many
as 100 million people a year and killing thousands, should be
interpreted as warnings.
Over the coming decades, global warming is likely to increase the range
and speed of the life cycle of the particular mosquitoes carrying these
viruses, encouraging their spread deeper into temperate countries like
the United States.
Recent research suggests that under a worst-case scenario, involving
continued high global emissions coupled with fast population growth, the
number of people exposed to the principal mosquito could more than
double, to as many as 8 billion or 9 billion by late this century from
roughly 4 billion today.
“As we get continued warming, it’s going to become more difficult to
control mosquitoes,” said Andrew Monaghan, who is studying the
interaction of climate and health at the National Center for Atmospheric
Research in Boulder, Colo. “The warmer it is, the faster they can
develop from egg to adult, and the faster they can incubate viruses.”
Already, climate change is suspected — though not proved — to have been
a factor in a string of disease outbreaks afflicting both people and
animals. These include the spread of malaria into the highlands of
eastern Africa, the rising incidence of Lyme disease in North America,
and the spread of a serious livestock ailment called bluetongue into
parts of Europe that were once too cold for it to thrive.
In interviews, experts noted that no epidemic was ever the result of a
Instead, epidemics always involve interactions among genes, ecology,
climate and human behavior, presenting profound difficulties for
scientists trying to tease apart the contributing factors. “The
complexity is enormous,” said Walter J. Tabachnick, a professor with the
Florida Medical Entomology Laboratory, a unit of the University of
Florida in Vero Beach.
The epidemics of Zika and dengue are cases in point. The viruses are
being transmitted largely by the yellow fever mosquito, Aedes aegypti.
That creature adapted long ago to live in human settlements, and
developed a concomitant taste for human blood.
Cities in the tropics, the climate zone most favorable to the mosquito,
have undergone explosive growth: Humanity passed a milestone a few years
ago when more than half the population had moved to urban areas. But
spending on health care and on basic public health infrastructure, like
water pipes and sewers, has not kept pace. Mosquito control has also
faltered in recent decades.
The mosquito lays its eggs in containers of water, of a sort that are
especially common in the huge slums of Latin American cities. With
unreliable access to piped water, people there store water in rooftop
cisterns, buckets and the like. Old tires and other debris can also
become mosquito habitat.
Water storage near homes is commonplace in areas where Zika has spread
rapidly, like the cities of Recife and Salvador in northeastern Brazil,
and where dengue experienced a surge in 2015, like São Paulo, Brazil’s
Altogether, dengue killed at least 839 people in Brazil in 2015, a 40
percent increase from the previous year. Worldwide, dengue is killing
more than 20,000 people a year.
Several experts said in interviews that a main reason for the disease
outbreaks was most likely the expansion of the number of people at risk,
through urbanization, population growth and international travel. They
see the changing climate as just another stress on top of a situation
that was already rife with peril.
While they do not understand to what degree rising temperatures and
other weather shifts may have contributed to the outbreaks, they do
understand some of the potential mechanisms.
The mosquitoes mostly live on flower nectar, but the female of the
species needs a meal of human blood to have enough protein to lay her
eggs. If she bites a person infected with dengue, Zika or any of several
other diseases, she picks up the virus.
The virus has to reproduce in the mosquito for a certain period before
it can be transmitted to another person in a subsequent bite. The higher
the air temperature, the shorter that incubation period. Moreover, up to
a point, higher temperatures cause the mosquitoes to mature faster.
With rising temperatures, “You’re actually speeding up the whole
reproductive cycle of the mosquitoes,” said Charles B. Beard, who heads
a unit in Fort Collins, Colo., studying insect-borne diseases for the
Centers for Disease Control and Prevention in Atlanta. “You get larger
populations, with more generations of mosquitoes, in a warmer, wetter
climate. You have this kind of amplification of the risk.”
Aedes aegypti is present across the southern tier of the United States.
Brief outbreaks of dengue have occurred recently at the warmest margins
of the country, and one is underway in Hawaii. But with pervasive window
screens and air-conditioning, the risk of disease transmission is far
less for most Americans than for people in poorer countries.
The mosquito does not thrive in areas with cold winters. Some research
suggests that continued climatic warming could allow the mosquito to
colonize more of North America in coming decades, though how much of a
disease risk that would represent is anybody’s guess.
The yellow fever mosquito competes with a cousin, the Asian tiger
mosquito, that has also colonized the United States, and is more
tolerant of cold weather. Whether one would beat out the other in a
hotter climate is unclear. Likewise, it is unclear how effective the
Asian tiger mosquito might become at transmitting Zika or dengue viruses.
In principle, the risk from continued global warming applies not just to
temperate countries, but to cities at high altitude in tropical
countries. Researchers are keeping a close eye on Mexico City, for instance.
With 21 million people in the city and its suburbs, Mexico City is the
largest metropolis of the Western Hemisphere. While the lowlands of
Mexico are plagued by yellow fever mosquitoes and the viruses they
transmit, the country’s capital sits on a mountain plain that has — up
to now — been too cold for the mosquitoes.
But temperatures are rising, and the mosquitoes have recently been
detected in low numbers near Mexico City. “The mosquito is just down the
hill, literally,” Dr. Monaghan said. “I think all the potential is there
to have virus transmission if climatic conditions become a bit more
Simon Romero contributed reporting.
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