The Mysterious Life Of The Cholera Bacterium

Scientists have long known that cholera is caused by a bacterium transmitted through food or water. But where does the bacterium live between epidemics, and what dictates the timing of new outbreaks? CDC cholera expert Eric Mintz discusses the bacterium behind the Haiti outbreak.

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JOE PALCA, host:

From NPR, this is SCIENCE FRIDAY. I'm Joe Palca. Over 600 people died of cholera in London during the outbreak of 1854. And it was a pretty mysterious disease back then. The prevailing medical theory of the day blamed it on contaminated vapors. But the English physician John Snow had his own theory. To prove it, he mapped out the cholera deaths during the outbreak, and he noticed that many of the deaths were concentrated around one particular water pump on Broad Street. Snow recommended disabling the pump. And sure enough, the outbreak was contained. So they knew it had something to do with water.

Thirty years after that, a German physician discovered the real culprit behind cholera outbreaks, a bacterium. Now, youd think that 150 years later we'd have pretty much solved all the problems and mysteries surrounding cholera. Well, not. There are still a lot of things that scientists are mystified by, like where cholera lives when it's not in infecting humans and why it flares up sometimes and not at others. Not to mention the latest outbreak - how did it get to Haiti and why now?

My next guest has been helping patients down in Haiti trying to keep the outbreak under control. Let me introduce him now. Eric Mintz is a medical epidemiologist in the Division of Foodborne, Waterborne and Environmental Diseases at the Centers for Disease Control and Prevention in Atlanta. He joins us by phone from Haiti today. Welcome to SCIENCE FRIDAY, Dr. Mintz.

Dr. ERIC MINTZ (Centers for Disease Control and Prevention): Thank you, Joe. It's a pleasure to be on the show.

PALCA: And if you'd like to join us and ask questions, the number is 800-989-8255. That's 1-800-989-TALK. And I'm very interested to of course this is a very pressing problem. Can you just give us a sense of how things are going there now?

Dr. MINTZ: Yes, I can. So the outbreak is still ongoing. The last figures I have are from October 27th, and a total of 4,722 cholera cases have been reported to the ministry of health here in Haiti at that time. And 303 deaths due to cholera had been reported.

PALCA: Mm-hmm. So any...

Dr. MINTZ: So we're working go ahead.

PALCA: No, no. I was just going to ask you. So why how did it happen? Why is it happening now?

Dr. MINTZ: Well, that is a great question. And it's one of the questions that, as you said, we scientists don't have any answer for. The vibrio cholerae bacteria that causes cholera is a free-living organism, it can survive in the natural environment. Its preferred home is brackish water, but it can survive in seawater or in freshwater, in rivers. And it infects humans from time to time in explosive outbreaks or epidemics and then lies relatively quiescent at other times. And we don't fully understand the ecology and the environmental factors that determine what the triggers are for those outbreaks or epidemics.

PALCA: Well, if you're not sure where it's coming from, do you have any idea why it gets transmitted so rapidly through a group?

Dr. MINTZ: Well, that much we do understand, thanks to the efforts of Dr. John Snow in the 1800s that you mentioned. Because cholera is a water-loving organism, most epidemics, most outbreaks are predominantly transmitted through water. And that water can be contaminated originally from in the environmental source of cholera, in the surface water, a body of water like a river. But as humans, as people become infected, become ill - and cholera causes a very profuse, watery diarrheal illness in some people - if the drinking water is not well protected, as was the case in London in 1854, then that water really becomes super contaminated, if you will, with loads of vibrios. And people who consume it are at high risk for getting ill themselves.

PALCA: So if you get one of the if you drink some water that has a few of this bacterium in it, are you going to get sick or might you get sick or are some people never going to get sick?

Dr. MINTZ: Well, I guess you could say all of the above. Many people will be exposed to the vibrio cholerae bacteria and won't develop any symptoms of illness, no diarrhea at all - in fact, about three quarters of people under an epidemic circumstance. And the other fourth, about 25 percent, will have diarrheal illness. Most of them, about two-thirds, will have a mild diarrheal illness. And a portion, oh, maybe a fifth or so will have a moderate diarrheal illness. They may go to a doctor. They can feel pretty bad. And then a small percentage, about two percent of the total of all those who were exposed, will develop cholera gravis, the most severe form of cholera. And that is a extremely profuse watery diarrhea, up to a liter or more an hour, accompanied by vomiting, and very rapidly can progress to dehydration and shock - and without proper treatment, will lead to death.

PALCA: And is there any indication why some go to the fulminating side and some just have the mild side?

Dr. MINTZ: Mm-hmm. There are several, several indications. One indication, one determinant is the dose of bacteria that you ingest. So the more you're exposed to those bacteria, the greater the risk that you'll develop more severe symptoms.

But other factors influence that. For example, the stomach is an acid barrier to bacteria. Vibrio cholerae, in particular, are very sensitive to acidity. People who have low gastric acidity, perhaps because they're taking antacids or young children, are therefore going to have more of the Vibrio get through their stomach and into the intestinal track. And that's were the cholera toxin does its damage and causes the diarrheal illness.

We've also noted in several studies that this can be influenced by blood group, and that people with blood group O, all other things being equal, are more likely to develop the severe form of cholera than people with other blood groups, A, B or AB. And the reasons for that are not well understood.

PALCA: No. So what's the treatment? Is there a treatment?

Dr. MINTZ: Thankfully, there is. There's a very simple treatment and that consists of replacing the fluid and the electrolytes, the sodium, potassium, the chloride and the bicarbonate that are lost through the diarrheal stool and/or through vomiting. If you can keep those - keep up with the losses by replacing that fluid volume in those electrolytes, the body can maintain its homeostasis and the patient, in all likelihood, will survive.

What happens is when people are - do not have that fluid and those electrolytes replaced, they quickly become dehydrated, they'll become shocky and die. And a mean - and the way to replace them is through a magic powder, oral rehydration salts, that's a mixture of the electrolytes I mentioned, plus glucose, sugar. And when that's mixed one packet with one liter of water, it contains exactly the right constituents to replace what's lost in this - in the diarrheal stool and in the vomitous. And so most people can be treated with, simply, oral rehydration. For those that come in severely dehydrated or are not able to drink sufficient amounts of oral rehydration solution, intravenous rehydration is used.

PALCA: Okay. Oh, let's take a call now and go to Don(ph) in Cincinnati, Ohio. Don, welcome to SCIENCE FRIDAY. You're on the air.

DON (Caller): Thank you. Has cholera been eradicated in the U.S.? And if so, when?

PALCA: Interesting question. What about...

DON: Thanks.

Dr. MINTZ: Mm-hmm, yeah. I guess we can say that epidemic cholera has been eradicated in the United States, long ago. The last time we've had epidemic cholera was in the 19th century. And at around the turn of the century, as we were coming in to the early 1900s, a lot was invested in water treatment plants and in water distribution systems, in our city's waste collection systems and waste systems, and a lot of attention was paid to hand washing and hygiene at that time. That was the sanitary revolution, occurred in Europe and the United States. And since then, we have never seen anything like the outbreak occurring here in Haiti, with thousands of cases.

We do have, in the United States, occasional sporadic cases, several a year. Many of those are in people who have traveled abroad to countries where cholera is endemic and have, you know, drunk the water or eaten some food that was contaminated, and developed illness on return to the United States. But we don't see secondary transmission within the United States. They don't infect others. And there's also some Vibrio cholerae off our own shores in the Gulf Coast. And we occasionally get a case of cholera in somebody who has eaten an oyster or a - some crustaceans, shellfish from the Gulf of Mexico, and they fail to properly cook it.

PALCA: Hmm.

Dr. MINTZ: And of course, cooking will cholera or other bacteria.

PALCA: Okay. Let's next go to Beth(ph) in Southfield, Michigan. Beth, welcome to SCIENCE FRIDAY. You're on the air.

BETH (Caller): Thank you. Hi. I have a - I had a grandmother who grew up in Poland and told the story of the cholera outbreak in her small village. And she believed that after going to the funerals of the first several victims or numerous victims, the rest of the village, nearly all of her village, was wiped out. And she believed that they contracted it from being at the cemetery and breathing the air over the other bodies that had been buried. And I'm wondering if that's a possible way of contracting cholera.

PALCA: Hmm, interesting. Dr. Mintz, what about that?

Dr. MINTZ: Well, that's a fascinating story. And that is indeed, that was the theory before John Snow's work in London. But every investigation done since has indicated that cholera is not transmitted by air. There's no risk to...

BETH: Oh.

Dr. MINTZ: ...acquiring cholera by breathing the air. However, your point is very well taken. There have been outbreaks, well-described outbreaks, that follow the funerals of cholera victims. And when investigated, those turn out to be, you know, either everybody was exposed before the funeral through the...

BETH: Mm-hmm.

Dr. MINTZ: ...drinking water. And the unlucky first victim, you know, is just the index case, if you will, the first case. But in some instances, people prepare food and handle the corpse, and there can be contamination of that food, the meal served at the funeral, if people are not very careful with the burial.

BETH: Ahh. Yes.

Dr. MINTZ: Those are precautions to be aware of.

PALCA: Okay, Beth. Thank you for that.

BETH: Thank you very much.

PALCA: Okay. We're talking with Dr. Eric Mintz from the CDC, who's in Haiti at the moment, dealing with, or helping to deal with the outbreak of cholera there. And we're taking your calls. I'm Joe Palca. And this is SCIENCE FRIDAY from NPR.

And let's take another call now and go to Aaron(ph) in - did I say that right? Aaron in Jacksonville, Florida. Welcome to SCIENCE FRIDAY.

AARON (Caller): That's right. I just wanted to know, the boiling water, will it prevent spread of cholera that would be the first key (unintelligible)?

PALCA: Boiling water. Okay. What about that, Dr. Mintz?

Dr. MINTZ: Well, boiling water is a very effective way to disinfect the water. And it will not only kill Vibrio cholerae, the bacteria that causes cholera, but it's a right way to make sure your water is free of any pathogen, any living organism that could cause infection or illness. It's not always possible to boil water here in Haiti. Unfortunately, there's a lot of deforestation and fuel is hard to come by, expensive, and it's just impractical to boil all the drinking water for a poor family here.

Another way to ensure that the water is safer to drink and free from Vibrio cholerae bacteria is to treat it with chlorine the way our water systems in the U.S. and in other countries are chlorinated. But if you're getting your water from a lake or a river, there's no chlorine in that surface water source. And there is a way, though, to chlorinate it in the home, to add a few drops of bleach or a tablet form of chlorine and to eliminate the Vibrio cholerae bacteria from water by chemical disinfection.

PALCA: And is that the key to controlling this epidemic to making sure that the water supply is cleared of this - of the bacterium?

Dr. MINTZ: I think that's a critical part of the key to controlling this epidemic, both in the cities where chlorine levels in municipal water systems can be brought up higher to make sure that they stay safe and free of cholera bacteria. But in rural areas, where people don't - aren't served by water systems, then this household water treatment is going to be a key component to protecting themselves and protecting their families from becoming infected.

PALCA: Okay. Let's go for one more caller and go to Dominick(ph) in St. Louis, Missouri. Dominic, welcome to SCIENCE FRIDAY.

DOMINICK (Caller): Hello, how are you?

PALCA: I'm very well.

DOMINICK: I'm Haitian. And there's a rumor in the Haitian community that the source of the cholera was from U.N. soldiers, Nepalese U.N. soldiers that were emptying their latrines upriver from where it happened. Is that true?

Dr. MINTZ: Well, I've heard that rumor. It is circulating here in Haiti, and we have no evidence at all to support it. It is certainly possible that cholera could have been introduced by a traveler from anywhere in the world, who may have had illness or may have been an asymptomatically infected person, someone with cholera but who had no symptoms, no diarrheal illness.

It's also through - possible that it could have come here through the environment, through water in the Caribbean Sea or perhaps through river water that, you know, may have had a small reservoir of Vibrios. And for environmental reasons we don't understand, that bloomed, someone became ill and started the cycle of increasing water contamination.

We really don't know the origin. And it's something we're interested in, but it's not going to be an easy question for us to find the answer to.

PALCA: So are things getting under control or is this still a situation that's out of control?

Dr. MINTZ: Well, they are stabilizing. And by that, I'm referring to the fact that the case fatality rate, the proportion of all the people who are ill that is dying, that's decreasing. In the beginning of a cholera epidemic, particularly in a country like Haiti where they have no recent experience with cholera before, people may not realize how serious it is, how severe it can be. And they may delay going to seek help for diarrhea.

PALCA: Yeah.

Dr. MINTZ: And the health care providers may not realize the severity and they may not treat it as aggressively as is needed to save a life of somebody with cholera.

PALCA: Okay. Dr. Mintz, I'm afraid I'm going to have to cut you off there...

Dr. MINTZ: That's all.

PALCA: ...because that's all the time we have. Dr. Eric Mintz is a medical epidemiologist in the Division of Food Borne, Waterborne and Environmental Diseases at the Centers for Disease Control and Prevention, Atlanta. Thanks for joining me today.

Dr. MINTZ: Thank you very much, Joe. Bye.

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