As if the decay and crime of West Baltimore aren’t bad enough, this neighborhood faces another menace as the weather begins to warm — mosquitoes, including types that can transmit diseases such as dengue, the chikungunya virus and Zika. The number of mature, biting Asian tiger mosquitoes that can be found in Baltimore’s poorer Harlem Park and Franklin Square neighborhoods in peak mosquito season (late summer) is roughly three times the number in wealthier areas of town, according to scientists who are studying the phenomenon.
And research has found that another mosquito species, Culex pipiens — which can carry West Nile virus — is more common in hard-hit urban areas and particularly has seemed to thrive in discarded-tire “habitats” in Baltimore.
“We find way more mosquitoes in the lower-income neighborhoods,” said Shannon LaDeau of the Cary Institute for Ecosystem Studies.
Since 2012, LaDeau and other scientists have been carrying out urban ecology studies of mosquitoes in the Baltimore and Washington areas. And they’ve reached some pretty dismaying preliminary conclusions.
“We see cases where there’s persistent trash and abandoned buildings, and it just creates this surface where there are lots of small bodies of water, which are just great for this mosquito,” said Dawn Biehler, a University of Maryland Baltimore County geographer involved in the work.
At a time when the water crisis in Flint, Mich., has raised awareness of the vulnerabilities of low-income or minority communities, the scientists say the recent Zika virus scare is exposing another looming form of environmental injustice. The Sandtown-Winchester/ Harlem Park neighborhood is 96 percent African-American, and nearly half of children here live below the poverty line.
“We have rampant economic, rampant health disparities,” said Baltimore City Health Commissioner Leana Wen. “And for us, the preparation for Zika brings to light even more acutely the disparities that are faced by our neighborhoods.”
Wen is heading a Zika preparedness group, convened by Baltimore Mayor Stephanie Rawlings-Blake, that is working across city agencies to prepare for the summer mosquito season.
Other urban areas are wrestling with the same combination of poverty and mosquito-borne disease risks. Research in New Jersey, conducted by Dina Fonseca and colleagues at the Rutgers Center for Vector Biology, similarly found that economic disparities were a good predictor of the abundance of the Asian tiger mosquito.
Comparing the wealthier and more suburban Monmouth County with the poorer and more urban Mercer County, which includes the city of Trenton, the study found that “poverty was positively correlated with number of [Asian tiger mosquitoes] captured and accounted for over half the variation.”
Fortunately, the climate in Baltimore and points north is not as hospitable for Aedes aegypti, the mosquito that poses the biggest threat for spreading Zika and other such diseases. But its fierce relative Aedes albopictus, or the Asian tiger mosquito, is here in force, at least in summertime.
The species got its U.S. foothold in Texas in 1985 and has since colonized much of the southeastern United States — with its range expected to further increase because of climate change. And it is also capable of spreading Zika and many others.
A number of U.S. health authorities have said that an outbreak at the scale of the current Zika scourge in Brazil or other nations in South or Central America is unlikely in this country, though there will certainly be isolated cases. One reason is a much greater prevalence of window screens and air conditioning; another is simply that in places such as Baltimore, winter comes around and stops mosquito activity every year. And unlike Aedes aegypti, the Asian tiger mosquito doesn’t exclusively bite humans — it’s more “opportunistic” and thus not quite as good a spreader of human disease, LaDeau said.
However, in low income communities, with less access in general to health care, symptoms may also be more likely to go unnoticed. “You’re probably less likely to get tested for any of these viruses,” LaDeau said.
In warmer and more southern cities such as New Orleans or Miami, there’s potentially a greater danger because of the more hospitable climate for Aedes aegypti and, again, relatively high poverty rates.
That’s what makes studying the urban ecology of disease-transmitting mosquitoes — and in this case, mosquitoes that breed in containers discarded by humans — so important.
“The way they breed, they like small containers. They need just a small amount of water,” Heather Goodman, a research specialist at the Cary Institute, said of Aedes albopictus. “Even a water cap, like on a water bottle — just a little bit of water, we can get larvae out of that.”
In an alleyway in Baltimore, Goodman tipped over a jar and a discarded tub of butter substitute that had both filled with rainwater — just two potential collectors out of so many littering the landscape.
The problem posed by waste situations such as this is that key mosquito species have adopted survival and reproductive strategies that depend upon the artificial urban environments created by humans. “You get a handful of species that can breed in that type of habitat, and when they do so they of course have no competitors and no predators, and you get huge population abundances,” LaDeau said.
When it comes to waste problems in Baltimore, in particular, residents regularly complain about the city picking up trash only once a week, Biehler said.
But then again, Baltimore is also a city that has seen its population shrink for decades, which lessens the tax base and, in turn, can erode city services. “It’s not just the city’s fault,” Biehler said. “There are bigger issues here.”
Wen, the city’s health commissioner, said the new Zika task force will be considering anything from sanitation to public education to counter mosquito threats. “The most important thing that we can do for stopping the propagation of mosquitoes is reduce the amount of standing water — in old tires, in containers, in swimming pools that aren’t being used — in every way across the city,” Wen said.
Wealthier areas are not exempt from concern about mosquitoes. In Midtown Baltimore’s Bolton Hill area, just over 3 percent of homes are vacant and abandoned, as opposed to over 30 percent in Sandtown-Winchester/Harlem Park, according to the Baltimore Neighborhood Indicators Alliance.
People are richer here, but that doesn’t prevent them from inadvertently creating mosquito-friendly environments with birdbaths, planters and other backyard and outdoor articles. It’s just nothing like landscapes of abandoned homes and piles of uncollected trash.
However, even though the wealthier neighborhoods have fewer mosquitoes, it may be that a higher percentage of the insects bite humans. One reason is that there are fewer opportunities for mosquitoes to bite other warm-blooded animals, such as the rats that also live amid urban decay.
“In the lower-income neighborhoods of West Baltimore, 60 percent of the blood meals are coming from rats and 30 percent humans,” LaDeau said, cautioning that the data is preliminary. “And the higher-income neighborhoods, where you do have fewer mosquitoes, the proportion of the bites are closer to 60 percent human.”
The research has also suggested another complicating factor — that when there’s little rainfall, mosquitoes may not actually thrive in poorer, rundown areas, because water does not collect in trash and debris. Rather, if folks in richer areas fill birdbaths and water plants during dry periods, they may actually be creating the greater mosquito draw.
That’s consistent with findings from New Jersey, said Fonseca, of Rutgers. “If you have more containers, you’re going to get more of these mosquitoes,” she said. “But if it’s a very dry year, areas that have nice lawns, and people are watering their lawns and keeping the containers full of water, ends up generating more mosquitoes.”
Further research will help illuminate the complex relationship between socioeconomic status, the state of the urban landscape and mosquito risk.
Rose Marie Brown, 72, has lived in Balitmore’s Sandtown-Winchester/Harlem Park neighborhood for decades and recently participated as a citizen scientist in National Science Foundation-supported research involving mosquitoes. After the project, Brown said she is ready to move away — but mosquitoes are just one factor driving her out. There’s also crime and rats.
“You had homeowners, and once they started dying off, you had renters come in and everything changed,” Brown said. “The dispositions changed. The thoughtfulness of cleaning and the attention to your home changed. They didn’t care, because they were renters.”