MELISSA BLOCK, host:

This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.

ROBERT SIEGEL, host:

And I'm Robert Siegel.

Our series Climate Connections returns to Peru today to explore how global warming may be changing patterns of infectious disease. The disease in question is cholera. An acute intestinal infection, it's caused by a bacteria and it's a persistent problem in some developing countries. Without treatment, between 25 and 50 percent of those who are infected will die.

Cholera hit Peru in the 1990s, a century after the last epidemic. Some scientists say the next outbreak could come sooner than that because of rising ocean temperatures.

NPR's Joanne Silberner visited two scientists in Peru who want to be ready.

JOANNE SILBERNER: Lima, Peru, is two cities. A city of upscale restaurants overlooking the ocean. A city of barefoot children begging in the streets.

The microbiology lab where scientist Ana Gil works is rich and poor. It has rudimentary equipment, a table and a basic microscope. But it does have Gil, an intent and enthusiastic cholera expert. She's holding a petri dish high up to the fluorescent lights. She stares at it closely and confers with her lab assistant.

(Soundbite of people talking)

SILBERNER: Gil is looking for the bacteria that cause cholera. Before 1991, no one in Peru could remember a cholera outbreak. Then, in a single day, it hit hard up and down the coast and took off from there.

Gil's husband, Claudio Lanata, is a doctor and her co-researcher. Lanata says people panicked.

Dr. CALUDIO LANATA (Senior Researcher, Nutritional Research Institute): When cholera hit us, nobody knew what to do, and they were thinking that people were going to die like flies.

SILBERNER: Cholera causes diarrhea so bad that people can die within a few hours. Lanata estimates about 14 million people in Peru were infected, and 350,000 ended up in the hospital.

Dr. LANATA: It was a very nasty disease, you just dehydrate very quickly. It's like you have opened a faucet in your system and just water comes out of you in large amounts ? liters and liters.

SILBERNER: Doctors quickly turned to an effective and inexpensive therapy - giving patients a water and salt solution. So the death rate was relatively low: 3,500 people. A smaller epidemic occurred in 1998. Both were linked to El Nino; that's a periodic and unpredictable weather disruption that leads to warmer ocean currents. Warm ocean currents can encourage the growth and spread of cholera bacteria.

Lanata and his wife, Ana Gil, are worried that global warming will bring cholera back. So Gil has scrounged up money left over from other projects to set up a rough surveillance system to find cholera before an epidemic takes hold.

(Soundbite of people selling fish)

SILBERNER: Ana Gil is starting her search at the same place that a cholera epidemic would start.

(Soundbite of people selling fish)

SILBERNER: Fishmongers sell the morning catch on the dock here on the outskirts of Lima. The silver gray fish glisten on the wooden tables in the morning sun, their dead eyes still bright and shiny.

Unidentified Fishmonger: Lisa, carilla, pintaria, (unintelligible)...

SILBERNER: What type of fish are these?

Dr. ANA GIL (Microbiologist): These are lisa, pintaria, pesepapa, a mixture of fish and frog...

SILBERNER: Fish are blamed for the cholera epidemics in Peru in the 1990s. The cholera bacteria were in the ocean and attached to plankton ? microscopic plants and animals that drift in the ocean. Fish and shellfish ate the infected plankton. People ate raw, infected seafood, and they got sick. Poor hygiene spread the disease to others.

In places like Lima, many people don't have access to clean drinking water or soap to wash their hands.

Unidentified Man: (Speaking in foreign language)

SILBERNER: Gil hires a creaky wooden fishing boat called Senior Dela (unintelligible). The boat is maybe 20 feet long with a bulky inboard motor. A little rowboat, its blue paint pealing, tags behind. Gil, in her beige Crocs, jumps in easily. She puts on a bright yellow lifejacket and settles down under a faded blue umbrella with scalloped edges.

(Soundbite of motor revving up)

SILBERNER: As the boat pulls away from the coast, Lima's bright green parks are quickly dwarfed by the desert dry hills behind it.

(Soundbite of motor stopping)

SILBERNER: A few hundred meters offshore, Gil's assistant, William Lopez, gets into the little rowboat. He throws a long, conical net overboard and circles the big fishing boat again and again.

Dr. GIL: (Speaking in foreign language)

SILBERNER: All around.

Dr. GIL: (Speaking in foreign language)

SILBERNER: He's dragging the net to catch as much plankton as possible so Gil can test it for bacteria.

Dr. GIL: And he will transfer that water into that flask. The water is very clear; it looks like there is not much plankton.

SILBERNER: Gil is also monitoring seawater temperature.

Dr. GIL: (Speaking in foreign language)

SILBERNER: Uh-huh.

Dr. GIL: 17.8 centigrade, yes.

SILBERNER: It's her first time checking water and plankton since the 1998 El Nino. She's in a hurry to get back to the lab. She walks quickly across the dock.

Dr. GIL: We get the plates; we get samples. And let's see what we can find in the lab.

SILBERNER: So it's back across town, past the gated campus of an agriculture university, past a potato research institute and at last, to the Nutrition Research Institute, the nonprofit where Gil works.

Gil's assistant carefully pours the precious sample into a beaker. It takes a few hours to filter out the plankton.

Dr. GIL: (Speaking in foreign language)

SILBERNER: Mid-afternoon, Gil takes a petri dish filled with jade green growth medium and dabs on some plankton. And now, she's holding that petri dish up to the light.

Dr. GIL: The reaction has to happen in the first 2 or 3 seconds. It's very fast.

SILBERNER: She looks anxiously at the dish.

Dr. GIL: It's clean. No cholera in our seawater yet.

SILBERNER: A quiet but momentous discovery. Good. Cholera isn't here, at least not yet. If Gil finds cholera, it won't be the first disease that climate change has brought to Peru. Her husband, Claudio Lanata, says dengue is back ? a mosquito-borne infection that causes high fever and great pain.

Dr. LANATA: You're now having diseases you didn't expect to have them at all. Dengue last summer hit us in Lima, and the mosquito is moving south because of the weather allows this to move.

SILBERNER: Gil suspects for cholera, it's just a matter of time.

Dr. GIL: Because of the sea temperature increasing, it will be the chance for the bacteria to grow faster, and it will be the beginning again of a new epidemic.

SILBERNER: The beginnings of a new epidemic?

Dr. GIL: Yeah.

SILBERNER: That's pretty scary.

Dr. GIL: Yeah, it is. That's why we have to be alert.

SILBERNER: If and when Gil and Lanata find cholera bacteria before an epidemic takes hold, they can at least warn people to cook fish thoroughly, boil the drinking water, and keep their hands clean ? or even try a new vaccine.

Joanne Silberner, NPR News.

SIEGEL: You can hear more stories on climate change at npr.org/climateconnections. We also have videos from around the world on climate science in action from Public Television's "Wild Chronicles."

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