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The New Diseases on Our Doorstep

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Borderline Cases: Dengue fever is on the rise in both Mexico and the United States, separated here by the Rio Grande.
Climate change and the movement of people and goods across our borders will force us to revamp our health-care defenses

Tiny, wizened, and sinewy, Maribel stepped on the leash of her snarling pit bull to keep it from attacking a group of uniformed men and women as they poked through the nooks and crannies of her home. It took all the strength the old woman could muster to hold the furious dog at bay, but she herself showed no sign of indignation at the invasion of her privacy. If anything, she looked resigned and slightly bemused. This lifelong resident of one of the poorest districts of Matamoros, the Mexican town just across the border from Brownsville, Texas, on the Gulf of Mexico, seemed to understand that the operation was, well, for her own good. The técnicos, a vector surveillance team organized and dispatched by the Matamoros Department of Health, were on a seek-and-destroy mission. Their target: mosquito larvae.

In recent days a fresh cluster of dengue fever cases had been confirmed in Maribel's neighborhood. Dengue is endemic in Matamoros; in 2004 a blood-sampling survey found dengue antibodies in 78 percent of the city's residents, which means all who tested positive had been infected with the virus at some point in their lives, though it may have gone undiagnosed. According to José Luís Robles López, the medical services coordinator for the city, dengue's grip has only tightened in the years since. It used to surge from August through October, in the wake of the summer rains, with cases leveling off throughout the rest of the year. But more and more, Robles López says, dengue is diagnosed steadily all year round.

The reasons are many, and Matamoros is not alone. Around the world, the incidence of dengue fever has risen thirtyfold in the last 50 years, with increases across all key indicators: the number of cases, the frequency of epidemics, the severity of the disease, and the geographic range over which outbreaks occur. Each year the virus is responsible for 50 million to 100 million infections, a half-million hospitalizations, and 22,000 deaths in more than 100 countries. Many experts believe that dengue is now the most worrisome arthropod-borne virus, or arbovirus, in the world (arthropods, which include insects, spiders, and crustaceans, have segmented body parts and an exoskeleton). And now it's making its way into the United States.

For most Americans, dengue remains an under-the-radar threat. But as the virus creeps northward, we need to be much more alert. The context for the disease has changed significantly and will continue to do so. Understanding more about dengue can also arm us with perspective on the evolving face of other vector-borne and infectious diseases (a vector is an agent, usually an arthropod, that carries a pathogen from one animal, or host, to another). Dengue's proliferation can be attributed to several interconnected factors: rising temperatures and altered rainfall patterns due to climate change, population booms in impoverished urban areas with inadequate municipal services, increased international travel and trade, compromised or dismantled mosquito-reduction programs, and the glut of man-made containers (especially those made of plastic or rubber) that serve as ideal mosquito breeding sites.

Some or all of these factors affect the transmission patterns of most arboviruses as well as other vector-borne diseases, such as Rocky Mountain spotted fever and Lyme disease, both of which are transmitted by ticks. Mosquito-borne arboviruses include West Nile virus, St. Louis encephalitis, equine encephalitis, chikungunya -- the list goes on. Scientists have documented hundreds of arboviruses. None is as entrenched as dengue, but many are spreading well beyond the areas in which they were originally identified and for which they're often named. Some, such as Lyme disease and West Nile virus, have already exacted a heavy toll on human health in the United States.

Zoonoses -- infections or diseases that are transmissible from vertebrate animals to humans -- add another level of complexity. Many, though far from all, are carried by a vector. But all zoonoses and arboviruses are influenced by a uniquely modern set of ecological disruptions: climate change, deforestation, human migration, urbanization, the intrusion of humans and domestic animals into areas where arthropods flourish, industrialized farming and animal husbandry, and so on.

What's clear is that effective control measures will require coordination across multiple scientific disciplines. "We need to cast a broader net," says Howard Frumkin, director of the National Center for Environmental Health at the Centers for Disease Control and Prevention (CDC). "Some of the health problems we face are new, others are reemergent, and the causes are ever more complex." Frumkin sees the need for communication channels to open among nontraditional partners, such as climate scientists and urban planners, park rangers and health departments, eco-database modelers and sewage engineers. The Brownsville-Matamoros border area, a dengue hot spot, focuses a lens on these issues. It demonstrates how pressing and complex the needs are, while at the same time suggesting ways in which collaborative efforts can begin to meet those needs before our health-care defenses are overwhelmed.

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Kim Larsen is a Brooklyn-based freelance writer. Her work has appeared in Discover, the Village Voice, and other publications.

I absolutely enjoyed this article, there should absolutely be a team effort to protect all of the living things on our planet, we only have one earth. Mother nature takes part in doing the destruction as is...We who inhabit this beautiful earth should be ashamed of the garbage that we do...We are letting all of our priorities get lost, we also must protect our bridges, roads, our main grids that keeps us lite, warm and informed.. I hope more people get to these law makers to get off their seats and some the insanity....

CORRECTION: And stop this insanity

My parents, 2 grandparents, a widowed aunt, 2 sisters and I tenanted a 2-acre frontage and a rental house that we made habitable. Dad drove a truck days, clerked 4 evenings; Aunt Mick went in to the news-stand at 0430, grandpa worked in a foundry. We grew & canned most of our food. We picked up coal in baskets all summer on railroad tracks across the field; we girls sewed and made over most of our clothes. All of us tended the garden and maintained the house and shed. There aren't enough policemen and sanitation workers to stop the global epidemics you describe. Every individual and culture needs to be responsible for their space. Educate people about the problem, require them to take care of their area, fine them or frog-march them into doing it, if they don't. Being poor doesn't entitle you to be a hazard to your community and a burden to others.

"protect all living things on earth"

uhh mosquitoes and pathogens are living things. this is a situation where hippy logic doesnt apply. disease agents are causing people to die, so we want to kill these things or prevent them from breeding.

The problems arising due to reckless use of natural wealtk lead us to many serious health problems.Dengue was seen as a disease of less priveledged and economically poor countries.But its surge in USA is seen as a very negative impact of global climatic change wich the USa needs totake special care due to her highly industrialised economy of the world.We in this art of the world need also to take extra careand re-orient our economic policies on the basis of eco friendly technology.

Seems to me that many illnesses are brought on by vectors like the dengue mosquito. We are working on developing an all natural repellent that repels (not kill but repel!) vectors like this and also ticks and flies. We think that using a soap or shampoo with this active ingredient as well as providing repellent lotion will go a long way toward mitigating these threats to our health.

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