U.S:- Feb. 16, 2017 - In one year, 2015, the Zika
virus leapt out of relative isolation in small groups of islands in the Pacific
and tore through the Americas, infecting an estimated 500,000 people in 40
countries. Most had only mild symptoms. But for many pregnant women, the virus
was devastating, inflicting grievous damage on the brain and nervous system of
their developing babies.
Among the many unanswered questions about the
Zika virus is this one: How did it suddenly spread so far, so fast? New studies
suggest that climate change may have been at least partly responsible for
Zika’s rapid spread.
“The climate conditions were very high risk
for having Zika transmission,” said Jonathan Patz, MD, director of the Global
Health Institute at the University of Wisconsin-Madison. Patz is studying how climate may have
impacted Zika’s sudden spread.
Zika was one of the case studies addressed at
the Climate and Health Meeting at the Carter Center in Atlanta. The meeting
became a political football last month after the CDC postponed it in January
ahead of President Donald Trump’s inauguration. Former Vice President Al Gore
salvaged the event and agreed to host it.
“We’ve had a few obstacles,” Gore said in a
statement opening the event. “The experts who were looking forward to this felt
it was valuable to go forward anyway.” Speakers at the conference talked about
the wide range of effects global warming and climate change are having on
public health: making plants like poison ivy more poisonous, making allergy
seasons longer and more intense, and increasing killer heat waves and smoggy
air.
Organizers didn’t shy away from jabs at the
Trump administration, which has been hostile to climate protections.
“As the climate changes, so will the
infectious diseases that we confront. More outbreaks like Ebola and Zika. More
pandemics like the bird flu. And here’s the catch: Walls will not keep these
pathogens out,” said Ashish Jha, MD, director of the Harvard Global Health
Institute, to appreciative murmurs and applause from the audience. “No borders
are going to protect us. That’s what awaits us unless we act.”
His quote was an apparent reference to
Trump’s pledge to build a wall along the U.S. border with Mexico.“There is a
clear warming trend, and it threatens our health,” said Kim Knowlton, DrPH, a
senior staff scientist at the Natural Resources Defense Council in New York.
***Zika's
Connections to Climate***
When Zika made its big move, 2015 was the
warmest year on record, according to NASA, and not by a small amount. It broke
the record by the largest margin ever recorded, boosted by a particularly
strong "super" El Nino weather pattern. In an El Nino year, the Pacific Ocean warms
near the equator, causing big shifts in weather around the globe. Some areas get far more rain than usual,
while others have droughts.
El Ninos don’t just bring changes to the
weather. Studies show they also bring spikes in disease.
For example, researchers studying nearly 2
decades of monthly reports of dengue fever in eight countries in Southeast Asia
found that the disease, which is closely related to Zika, became far worse
during El Nino years. During these warmer years, dengue fever spread farther,
faster and infected more people than years when the average temperatures were
cooler.
Patz said that makes sense, given what we
know about the biology of the type of mosquitoes that spread not only dengue,
but Zika and other kinds of infections, too.
“With any viruses carried by mosquitoes,
warmer temperatures give you a faster development. Oftentimes mosquitoes are
smaller when they hatch in warmer conditions, and they have more frequent
feeding behavior to get enough blood for their blood meal to develop their
eggs,” he said.
That means mosquitoes bite more often in
warmer years, making them more likely to transmit disease. Warmer temperatures
also speed up the rate at which viruses move through the mosquito and become
able to infect people.
“It was pretty striking, as far as how hot
the temperatures were in Brazil 2 years ago,” Patz said. “I wouldn’t be
surprised if there was as strong a parallel between temperature and Zika as
there is with dengue.”
Since 2016 has since surpassed 2015 as the
hottest, researchers say we should expect to see more outbreaks like Zika, and
not just from diseases passed to humans from animals. Waterborne diseases like
cholera and vibriosis, which people get from eating oysters contaminated with
vibrio bacteria, are becoming more common as the world’s waters get warmer.
Blooms of toxic algae, which poison both sea life and people, have become more
of a threat. In his keynote address, Gore showed a slide depicting a massive
algal bloom in the Pacific Ocean in 2015, which he noted closed fisheries from
Alaska to Mexico.
“We’re seeing more emergence of new
pathogens,” said Christine Johnson, PhD, DVM, head of global surveillance for
the PREDICT center at the University of California at Davis. PREDICT is a government-funded program that
keeps tabs on how new diseases pass from animals to people.
She pointed to re-emerging viruses like Rift
Valley fever, which humans catch from herd animals like sheep and cattle and
has caused recent outbreaks in Africa, and yellow fever, a disease carried by
mosquitoes that’s recently had a resurgence in Africa and South America.
Another example is Middle East respiratory
syndrome, or MERS, which was first reported in 2012. It's caused by a virus
that passes from camels to people. Johnson said there are several reasons
behind the increase. For one thing, we’re better at finding new diseases. And
humans keep encroaching on once-wild places, putting us in closer contact with
the animals that host viruses and bacteria that are new to humans.
But those changes don’t explain the increase
entirely, and climate change, she said, is certainly playing a role. “There’s
no question that the pace is increasing,” she said.
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