[Marxism] In Zika Epidemic, a Warning on Climate Change

Louis Proyect 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 
coincidence?

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 
single variable.

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 
largest state.

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 
suitable.”

Simon Romero contributed reporting.



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