Streams

Degrees of Concern - Part IV

Thursday, October 09, 2003

A few years ago, a group of leading researchers published a report on climate change and its human heath impacts. They concluded that changes in rainfall, temperature and other weather variables may affect the rate of vector-borne illnesses spread by ticks, mosquitoes and other carriers - illnesses such as West Nile Virus, Hunta Virus, Lyme Disease and Malaria. They also wrote that non-weather factors such as human behavior and the ability of public health infrastructures to cope with outbreaks would also play a big role. New York City was the first place in North America to experience an outbreak of West Nile virus. By last year, it had spread to 44 states, causing more than 4000 illnesses. More than 280 people in the US have died from West Nile, most of them elderly.Our series "Degrees of Concern" continues now as John Rudolph explains how West Nile came to the city and how it has changed the way New Yorkers live.

[Sound of engine revving, spraying, footsteps and birds]
Late on a hot summer afternoon, James Gibson stands in Staten Island's Willowbrook Park. He's thumbing through maps of the area and swatting at the occasional mosquito. Gibson is the Assistant Commissioner for Veterinary and Pest Control Services at New York City's Department of Health. On this day he's overseeing a fleet of spray trucks, the latest weapons in the city's war against mosquitoes that carry West Nile Virus.

GIBSON: We're using an applicator called an ultra-low-volume applicator, which is as it describes. It uses very low amounts of pesticide. It's in very tiny droplets and basically what happens is the droplets hit the mosquitoes in flight and actually kills them in flight.

[sound of ATV coming off its blocks]
Gibson's convoy heads into the park. In addition to the spray trucks, the entourage also includes a three-wheeled all-terrain vehicle. Its driver wears a hooded body suit and a gas mask. A portable loudspeaker warns people along the spray route to take cover.

GUILIANI-LIKE VOICE: The city is applying pesticide to reduce the threat of West Nile virus. To minimize exposure to the pesticide please go indoors immediately, until the trucks have passed

Mosquitoes have turned out to be tenacious opponents as they buzz around backyards, parks and abandoned lots. The spraying targets them with a lethal, and controversial, pesticide.

GIBSON: What we use is a pesticide called anvil 10 + 10 it's a synthetic pyrethroid and it's been shown to be very effective at killing mosquitoes.

After lengthy review, the city's Department of Health concluded that spraying the chemical to control West Nile Virus does not present a significant risk to public health. But its impact on humans is in dispute. Andrew Darrel is the New York regional director for the group, Environmental Defense.

DARREL: It can irritate the breathing, in some studies there has been shown an estrogen-like link to breast cancer over the long term, but generally, anvil is recognized by the EPA as one of the safer pesticides to use in a situation like this. But like any pesticide or larvicide, this is a chemical that is designed to kill things, so it - common sense would suggest that if spraying is going on in your neighborhood, in your community, it's probably best to stay away from the stuff.

Darrell argues that any kind of spraying should be considered an absolute last resort. This year's mosquito eradication campaign began in April, with an effort to kill mosquitoes where they breed, in pools of standing water.

FRIEDEN: We apply larvacide quite widely.

New York City Health Commissioner Thomas Frieden:

FRIEDEN: We also track the virus in a way that we're told by CDC really is unique in the country. We have a very extensive set of light and gravid traps, basically fancy ways to track mosquitoes and on a periodic basis, weekly or daily if we need to, to see which kinds of mosquitoes and we speciate them. Last year, we tested more than 100,000 mosquitoes for WNV to figure out what kinds of mosquitoes are where, how many of them are where, and whether they're infected with the WNV.

In addition to these advanced bug-killing techniques, Commissioner Frieden says the most effective defense against West Nile Virus may be something more basic, and perhaps more difficult to achieve: changing human behavior.

DARREL: People can protect themselves by wearing long-sleeved shirts and wearing DEET when they're out between dusk and dawn. And they can protect their neighborhoods by getting rid of standing water and calling 311 if they see a dead bird because that helps us to track the spread of the virus.

To force New Yorkers to change their habits the Health Department now issues fines to people who don't get rid of standing water on their property. They also distribute cans of bug spray to those who are most vulnerable to West Nile Virus - elderly people.

For some, the battle against West Nile and the mosquitoes that carry the virus ends here. But others go back to the original outbreak of West Nile Virus and see an ominous connection between the sudden appearance of this new disease and unusual weather patterns that may be linked to climate change.

[From NPR, September 7, 1999 Rebecca PERL]: Two elderly New York residents have died /// three more cases of Saint Louis Encephalitis have been confirmed, and dozens more are suspected. Holiday barbecues and other plans were abandoned as

The arrival of West Nile Virus in New York can be traced to the summer of 1999 when people started showing up at hospitals in northern Queens complaining of severe headaches, confusion, nausea, fevers. By Labor Day, health officials thought they knew what the problem was.

[From NPR, September 7, 1999 Rebecca PERL]: Health officials aren't completely sure why they are seeing Saint Louis Encephalitis all of a sudden in New York, but suspect the hot, dry summer weather, which is favored by the type of mosquito that is a carrier.

The deaths were shocking. But by focusing on the toll in human lives health officials missed an important clue. It took a few weeks before investigators noticed the illness was also killing birds.

Dickson Despommier is a professor of environmental health sciences at Columbia University's Mailman School of Public Health.

DESPOMMIER: The veterinarians became alerted to the fact that not only were birds dying outside the zoo, but they were also dying inside the zoo, and exotic birds at that. As it turned out, only birds that lived in the Western Hemisphere were dying. All the birds from Africa didn't seem to be affected.

Since St. Louis encephalitis doesn't kill birds in this country, health officials realized they were dealing with a different disease. But what was it?

Based on DNA matching, the pathogen killing both birds and humans was soon correctly identified as West Nile Virus. West Nile is common in Africa, West Asia and the Middle East, where many birds have developed an immunity to it. The virus had never been seen in North America.

How did it get to New York and why did it spread so quickly? Many researchers suspect West Nile Virus may have hitched a ride on an infected person or mosquito traveling from the Middle East. As to its rapid spread, Despommier believes the weather may have played a key role. The summer of 1999 was the hottest and driest the city had experienced in 100 years. These extreme conditions may have allowed the virus to get a foothold.

DESPOMMIER: There were six days in July over 100 degrees. From May 23 until August, there was no rain whatsoever. We had numbers of days that were above 100 degrees. So, the virus multiplies like crazy inside these vectors. Now every bite has the potential for injecting lots of virus particles.

Most people think of mosquitoes as wet weather pests. But dry conditions actually make them more lethal. The lack of rain creates a concentrated, polluted mix in breeding pools where mosquitoes thrive. Hot temperatures speed up the mosquitoes' life cycle. These conditions have been blamed for several West Nile outbreaks, according to Paul Epstein of the center for health and the global environment at Harvard Medical School.

EPSTEIN: West Nile's largest outbreaks in the 90s in Romania, in Russia, in Israel, and in NY in 1999, were all associated with severe droughts.

For Epstein, those droughts were abnormal occurrences associated with climate change.

EPSTEIN: Heat in the atmosphere in the oceans is changing the water cycle, affecting the intensity, duration and geographic patters of precipitation. These are fundamental to where mosquitoes breed, so in addition to warming, it's these extremes and wide oscillations from droughts, punctuated by heavy rains that are key to destabilizing the biological systems.

GUBLER: To say that climate change has been responsible for epidemics like West Nile is really stretching it.

For the past five years Duane Gubler of the Centers for Disease Control, has led that agency's response to the West Nile outbreak.

GUBLER: Climate change can influence transmission patterns, but it's a slow process, and the thing that causes epidemics is not climate change but the introduction of the right virus into the right place where there's a susceptible vertebrate population.

In the case of West Nile, there were plenty of local mosquitoes and birds to carry it, and an entire human population with no immunity against it. In much the same way that a public health campaign finally eradicated malaria in the U.S. in the 1950s, today, public health departments, Gubler says, should be able to deal with West Nile, even in a warmer world.

GUBLER: climate change, per se, should have little or no impact on public health, if public health officials and the communities do what they're supposed to do, and that is to develop good public health programs that will mitigate any maj-, any minor changes in temperature that may occur over a period of time.

But others researchers see New York's West Nile outbreak as an opportunity to begin to understand the connection between climate and the spread of disease. Kim Knowlton studies the health impacts of climate change at Columbia University's Mailman School of Public Health.

KNOWLTON: The climate models, the global climate models, are predicting that in future, not only is the trend of warming going to continue as a result of both natural and anthropogenic causes, sources of greenhouse gasses, but that the variability of weather on shorter timeframes is also going to increase. So West Nile has been a great way to sort of get our legs and get our surveillance methods improved and also start this discussion. What comes next? What do we do?

One thing scientists are doing is developing a vaccine against West Nile. Human tests at the National Institute of Allergy and Infectious Disease begin later this year. An effective vaccine could go a long way toward making people feel more secure against the virus. The question some researchers continue to ask is whether West Nile will be followed by other diseases whose spread is encouraged by the warming of the world's climate.

More on the Degrees of Concern series by John Rudolph

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