By now, the stark projections are well-known. Climate change will cause at least 4.7 meters of sea level rise over the next few decades, inundating the coastal cities in which a large percentage of the global population lives. Meanwhile, climate change is inducing heavier precipitation in shorter periods of time — exacerbating problems at the coasts, and imperiling places from the American Midwest to the Amazon.
The implications are difficult to stomach, but easy enough to understand: loss of property, mass migration and even death. Harder to imagine and less often stated, however, is that flooding can change the urban ecosystem — and lead to epidemics of disabling and deadly disease. This is an emerging problem in the Caribbean, Central America and South America, where shifts in climate have opened the door to vast epidemics of two infections that cause debilitating arthritis and neurological impairments in babies.
The same urban-dwelling insect spreads both diseases: the mosquito. While cities consider how to grapple with rising water, can urban planners and health officials also tackle what some call “the deadliest animal in the world”?
Though the insect is not itself infectious, there’s a reason for the lethal reputation. Mosquitos consume the blood of other animals, including humans, and carry that infected blood from one body to another. A mosquito genus called Anopheles transmits malaria, which currently kills about 500,000 to 600,000 people per year, for instance. Thus far, experts attempting to prevent outbreaks have tried everything from policing control-thwarting pharmaceutical scams to genetically modifying Anopheles’ DNA, with mixed success.
To fight mosquito-borne disease on this level, however, involves a certain amount of information on the nature of a given infection. And the Americas’ latest mosquito-borne epidemics, chikungunya virus and zika virus, are not yet fully understood.
Chikungunya is not new, strictly speaking. The disease is thought to have emerged in the 1700s in Tanzania. There, sufferers named it a word in the Makonde language meaning “that which bends up,” evoking the acute fever and extreme joint pain that characterize the disease. The virus caused occasional outbreaks in Africa, Asia and Europe for centuries. Modern scientists isolated the virus by 1953. But in the six decades since, it has remained a “neglected tropical disease” — in part because it spread little and infected few.
That changed in 2013, when a chikungunya epidemic swept across the Caribbean. After emerging in French Martinique, the disease steadily spread to almost every Caribbean island nation. It moved as far south as Venezuela and Colombia (where a total of nearly 30,000 people were infected) and as far north as the U.S. and Canada (although only through a few cases imported by travelers). By November 2014, the Pan-American Health Organization counted 878,745 suspected cases.
The outbreak didn’t garner the frequent international headlines that Ebola did in the same timeframe — even though the number of people infected with chikungunya was an incredible 30 times larger than the 28,601 people afflicted with Ebola. Public awareness likely comes down to fear of lethality. While 11,300 people died of Ebola (or almost four of every 10), just 154 — or less than two of every 10,000 people infected — died of chikungunya.
That said, the disease isn’t harmless. There is no effective immunization, treatment or cure. Studies following up on patients after acute infection have established that the majority suffer a months- or years-long bout of arthritis. The disease that bends up tends to leave people bent for a long time.
Worse yet is zika virus, which has been rapidly spreading in Brazil since May 2015, has infected people in Colombia, El Salvador, Guatemala, Mexico, Paraguay, Panama, Suriname and Venezuela, and has just reached Puerto Rico this week. The disease, which was first identified in Uganda in 1947, was formerly rare and confined to a few Pacific Islands. There, it caused an illness of fever, joint pain and skin rash similar to chikungunya.
But zika has jumped to South America — and there it’s also causing microcephaly in the infants of women infected with the virus early in their pregnancies. Microcephaly is a developmental condition in which a fetus’s head does not grow to normal size, causing a smaller brain and lasting neurological impairment. Thus far, 1,250 infants have been affected in Brazil. Health officials aren’t yet sure why.
To cope with the latest diseases, therefore, the best efforts might be focused on the urban ecosystem. Luckily, we know the mosquito species that causes chikungunya and zika is Aedes aegypti, the same one that carries dengue fever. William Pan, a Duke professor working to quell infectious disease in Peru, points out that a key trait of the species is their urban habitat: “Aedes aegypti lives in an urban area. You will never find an Aedes aegypti mosquito in the forest.”
Fighting the city-loving mosquito is straightforward, if challenging. Mosquitos spread with flood- and rainfall-driven increases in standing water, the environment in which the insects breed. (As Pan notes, “If there are floods or there’s more water availability in general, it increases the burden to deal with all sorts of diseases.”) Getting rid of egg-contaminated water, then, is a good first step. Luckily, infectious disease control efforts tend to carry over from one disease to another — and because dengue fever has long been present in Latin America, programs exist to address it. In Cuba and elsewhere, these efforts have succeeded at engaging the public in keeping water tanks covered and treated with insecticide, often holding disease and death to a minimum.
In a time of flooding induced by climate change and El Niño, however, that effort will be more necessary — and tougher — than ever before. Paraguay, which had its first large outbreak of chikungunya last year, has implemented a comprehensive virus control plan, for instance. But amid flooding, which last week displaced some 200,000 people, its implementation remains uncertain.
The “Health Horizons: Innovation and the Informal Economy” column is made possible with the support of the Rockefeller Foundation.