Warm Summer May Spread Zika to NYC, Los Angeles, Study Says

  • Virus carried by mosquito that thrives in urban areas
  • Zika being investigated for possible link to birth defects

Summer weather may be warm enough to allow the mosquito carrying the Zika virus to spread as far north as New York and across the western U.S. to Los Angeles, according to a study by the National Center for Atmospheric Research in Boulder, Colorado.

Long-range forecasts call for a 40 percent to 45 percent chance that summer temperatures will be warmer than normal, allowing populations of the Aedes aegypti mosquito, blamed for spreading the virus in Latin America and the Caribbean, to expand their range, according to models run by NCAR and NASA’s Marshall Space Flight Center.

“Even if the virus is transmitted here in the continental U.S., a quick response can reduce its impact,” Mary Hayden, co-author of the study and a medical anthropologist with NCAR, said in a statement.

The Zika virus was found in Uganda in 1947 and has moved through the world’s tropical regions during the past 10 years, the researchers said. It reached Brazil last year and more than 20 countries now face pandemics.

Zika’s Symptoms

For most people, the disease causes mild flu-like symptoms that clear up in about a week. “However, scientists are investigating whether contracting the disease during pregnancy can lead to microcephaly, a rare birth defect characterized by an abnormally small head and brain damage,” according to the statement.

In order to predict its spread, researchers used two models to simulate weather conditions and the mosquitoes’ life cycle across 50 cities in the U.S., according to the paper, published Wednesday in PLOS Currents Outbreaks.

The insects, known to thrive in urban areas, rely on warm temperatures and water-filled containers such as buckets, barrels and old tires in order to hatch their eggs. The research suggest conditions start to become favorable across the Southeastern U.S. and parts of Arizona in April. By June, all 50 cities in the study had the potential for being home to at least some mosquitoes, including St. Louis and Denver, where the insect hasn’t been detected yet, the study said.

Outside of southern Florida and southern Texas, most of the U.S. is too cold for the species in the winter, according to the researchers. A relative, the Aedes albopictus or tiger mosquito, can survive in colder climates and has spread the virus in other parts of the world, but there isn’t evidence of it doing so in the U.S., said Andrew Monaghan, an NCAR scientist and lead author of the paper.

Mosquito’s Limits

Aedes aegypti “is fairly well constrained by temperature and water availability,” he said. “Usually they can find water, so temperature becomes the factor.”

For the disease to spread in New York, the mosquito would have to be able to gain a foothold from the weather and then be able to bite hosts that had Zika, Monaghan said. The insect’s entire life-cycle lasts eight to 10 days, according to the Centers for Disease Control.

“Typically they are not born with the virus,” Monaghan said. “They have to bite someone with the virus.”

Given the number of people who travel to and from New York, there is a chance both conditions could be met, he said, though he rates the odds of a large outbreak to be low. 

The mosquito isn’t a stranger to the U.S. East Coast, Monaghan said. It’s also responsible for dengue fever, and there was a large outbreak of that disease in Philadelphia in the 18th century.

“Lower-income residents can be more exposed to mosquito bites if they live in non-air conditioned houses or have torn or missing screens,” the study said.

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