Tracking the Global Spread of Cholera

Naked Scientist Kate Lamble spoke to PhD student Ankur Mutreja from the Sanger Institute to discuss his work; sequencing the genome of cholera bacteria in order to track the 7th pandemic of the disease.

Ankur - So, my PhD really is all about to study the evolution of the bacteria which causes cholera and based on that to actually track the spread of this bacteria globally.

Kate - How did you first get interested in cholera specifically as a disease?

Ankur - I come from India and although I come from North India, I've heard about cholera a lot since I was a child and I've in fact, seen a cholera outbreak in my region. So, when I got some opportunity to do some cholera work, it really excited me and most of the samples, as they were coming from India and Bangladesh, those places being endemic, they just really hooked me up and I thought have to do with this as my PhD.

Kate - So, why would we want to watch how the bacteria of cholera changes over time?

Ankur - After doing this, we can plot the family tree, if you like, of this bacteria and we can find out the ancestor of this bacteria and we can precisely actually tell when those ancestors existed and where those ancestors were based.  From that, you can basically track the spread of this bacteria backwards.

Kate - How do you find out how the bacteria is related to a family tree?

Ankur - Okay, so what you basically do is, you take the bacteria, you isolate the genome which is basically the DNA and then you sequence the DNA of that bacteria, and in those genomes, you then see the difference is among those DNAs.  And based on those differences, you can see which bacteria group together and which bacteria separate.  So, that's how you can draw the phylogenetic tree or a family tree for that bacteria and you can track the spread.

Kate - How does tracing this and seeing how it's spread help us in tackling the disease?

Ankur - So, once you have tracked the particular spread, you know what particular type of bacteria is around these days which is causing more severe disease if you like.  So, if then you see a disease anywhere, where it wasn't there or if someone has got it new, you can see if that bacteria matches that particular type of bacteria and then you'll be quicker in taking actions because you know much more about that bacteria already.

Kate - So, by following it, if it moves from India to Bangladesh, we can take those lessons that we learned from India and apply them in Bangladesh.

Ankur -  Absolutely. So, if a bacteria has spread with people, with travel, so our study showed that this bacteria can travel with people. They can be carriers where they can be export and import a food which could result in transfer of these bacteria. So, these are the lessons we've learned. We can control this in the future.

Kate - Who's able to use that data?

Ankur - Essentially, everyone can use this data including public health parties. It's up to them how they want to use this. So, if they want to use it, they'll see. Then in fact, the antibiotic resistance actually came in to these bacteria. So, based on that, they can do their decisions.

Kate - So, you can look at how bacteria becomes antibiotically resistant. How does that help tackling it from a public health point of view?

Ankur - So, if a bacteria has gained a particular type of antibiotic resistance, obviously, that antibiotic would not treat that disease and then when you have tracked that particular type of bacteria and you know this is the bacteria which had that type of resistance, you wouldn't be using that resistant - that antibiotic again against that bacteria, so you'll try a new antibiotic, you'll try a new therapy approach.

Kate - So, you can forewarn doctors about what to use and also, what to stockpile I suppose.

Ankur - That's right.

Kate - How different is the bacteria you find nowadays from one you'd find 100 years ago?

Ankur - It is very different, I would say. So, the bacteria which caused let's say an outbreak in London which was traced by John Snow, it was a classical biotype and we are into 7^th pandemic now which is from a bacteria which is called El Tor biotype. This is a particular type of bacteria which is causing this pandemic.

Kate - What do you mean by a pandemic?

Ankur - So, a pandemic means a global spread. So, all the strains of the 7^th pandemic come from the source and we identified a single source which is Bay of Bengal. Strains move from that particular source, entering to a known endemic country, let's say for example, a country in Africa. They would go there, cause an outbreak and then disappear, and that's where we call the end of the wave. So, 1961 was when the first case of this 7^th pandemic causing bacteria was reported. That is not really the beginning of the pandemic. We traced back this pandemic, actually started in 1910.

Kate - So, you were describing the waves there and every single one seems to have come from the Bay of Bengal. Why is that area such a cauldron for cholera bacteria?

Ankur - So, if you look at the world map, the Bay of Bengal has a very unique position and where it actually exists, it has the right temperature for the bacteria to grow and population there is going to the Bay of Bengal, collecting water to drink and all the sewage systems at times are actually draining into Bay of Bengal as well. So, it kind of gives a very good habitat, let's say for the bacteria to grow and to multiply.

Kate - So, it's a good habitat for the bacteria and then like the human conditions around it are good for transport to other areas.

Ankur - Absolutely, human conditions are helper conditions to actually help bacteria travel to different places.

Kate - If there's been 7 pandemics and each time it's receded and you mentioned it just goes in waves, does that imply that cholera is quite tackleable as a disease?

Ankur - So, it is. It can be tackled, but you have to have very precise idea about what exactly was happening in that wave, what sort of public health action was taken in a particular country to tackle that and from there, you learn lessons.

Kate - Is that shown in the waves within the 7^th pandemic? Have we got better reacting to each wave?

Ankur - We have got better, but at the same time, bacteria has become better as well at causing disease. So you know, bacteria keeps evolving, it keeps changing. So, each time it gets better, we need to get even better.