Rat relief? NSF-funded molecular ecologist Michael Blum shares some surprising results from his team's tracking of pathogen-carrying rodents after disasters

NSF's Weather or Not!

Rat relief? NSF-funded molecular ecologist Michael Blum shares some surprising results from his team's tracking of pathogen-carrying rodents after disasters

National Science Foundation


Rat relief? NSF-funded molecular ecologist Michael Blum shares some surprising results from his team's tracking of pathogen-carrying rodents after disasters. His data may pave the way for a mathematical model that could simulate how environmental changes, natural or man-made, affect populations of rodents that carry pathogens hazardous to humans.
Interviewer: Charlie Heck

Interviewee: Michael Blum

CHARLIE: Rat pack, rodent revolution, vicious vermin -- let’s chat about rats.

CHARLIE: Did you know…a rat can fall as far as 50 feet and land perfectly fine…or… that rat’s front teeth grow 4½ to 5½ inches each year because they chew on everything! What about this one: A rat can tread water for three days, that’s right, three days.

CHARLIE: What about their behavior after a natural disaster? Think that’s not important, well you might think again…because new rat research aims to provide urban communities better data on disease carrying dangers and where to look for them after the storm 5, 10, even 20 years in the future.

MICHAEL: Cities and state and federal agencies in a disaster scenario, they go into an area, an affected area, and their aim is to reduce as much risk to public health and human well-being as possible. And so actions are taken, for example, clearing debris, clearing vegetation, putting what we refer to as mosquito fish in standing waters to reduce mosquito larval loads. All these things are intended to reduce risk to humans in areas that have been devastated. And what we're interested in knowing is do some of these decisions, do some of these actions that are taken during disaster recovery have ripple effects five, ten, 20 years later that actually counterintuitively increase risk over time rather than reduce risk over time.

CHARLIE: That’s Michael Blum, he’s a molecular ecologist at Tulane University. Blum and his team have been studying rats and where they set up their humble abode post natural disasters. His data may pave the way for a mathematical model that could simulate how environmental changes, natural or man-made, affect populations of rodents that carry pathogens hazardous to humans.

CHARLIE: So, I know exactly what you’re thinking and will tackle that first -- why rats? Blum says they’re sort of a symbol for how communities within an urban area respond to a catastrophe. His team is focusing on the outcomes of Hurricane Katrina. Not necessarily a before and after but more of a cause and effect model that can be applied to other natural disaster recoveries.

MICHAEL: We decided to focus on the interplay with respect to infectious disease because in many respects responses to catastrophes and disasters really trying to diminish risk exposure. And so if you think about what disasters bring about-- flooded landscapes or the built environment being broken-- the idea is that through recovery processes the decisions that are made to change the environment can change an exposure risk. And so that was certainly the case in New Orleans after Katrina.

CHARLIE: That brings us to risk exposure versus risk perception. Blum says there’s a big difference between where we -- humans -- perceive rats live and where they actually do in disaster-stricken areas. Spoiler alert, it’s not what you think…

MICHAEL: It's very simple, so there are physical risk dimensions. For example, where rats live across the city. And then there's our perceptions of where rats are across the city. And they may very well not be connected to one another. So if you go out into your street or you go out into your backyard and you see something move you may detect or you may think it's a rat, but it may be a raccoon. It may be a possum. It may be nothing at all. It may be a shadow. But there is that perception of risk.

CHARLIE: Blum illustrates the difference between post-disaster rats and urbanite rodents with a good ol’ fashioned rat battle – NYC verses the Big Easy.

MICHAEL: Much of what we are seeing about rats in general, what people are thinking, what people are talking about is coming from New York City as you might imagine. I wouldn't say that they pride themselves on being the rattiest city in the world, but there's a certain relationship that they have with rats. So, it tends to attract attention, and there's been some recent efforts to collate all the information that people have about risk perception, about these 311 complaint calls that are archived.

MICHAEL: And so what people have been doing is mapping out the distribution of those calls to get a sense of where rats are concentrated in cities, and it upholds a basic principle, which is rats follow humans. So the more humans there are, the more rats there are. But what we're finding in New Orleans and we think that this probably holds more generally is that if you map risk perception, so these 311 call data against very intensive quantitative estimates of population structure, population demography, we don't see that relationship. So, we in fact see an inverse relationship. So where there are fewer people, there are more rats. And it may be that this is general across cities. It may be that this is only particular to post-disaster landscapes.

MICHAEL: But what we're finding in New Orleans is that the distribution abundance of rats in the city maps onto abandonment. So areas where populations have been reduced because they haven't recovered since Hurricane Katrina, those areas typically have higher levels of vacant lots, areas that are more abandoned. And those are the areas where we're seeing high concentrations of rodents in cities. So this one to one relationship that's been viewed as being sort of principal in other cities, particularly in New York, doesn't hold in New Orleans.

MICHAEL: And what I'd say is that it's hard to say who's right and who's wrong. But our study is the first and only study that has very clearly and carefully mapped these 311 call data to quantitative estimates, those population demography.

CHARLIE: Now that we’ve dispelled a tale tell amongst our rodent residents inhabiting post-natural disaster urban areas, let’s tackle a fact -- they can carry human diseases.

CHARLIE: Blum’s team has a part two to their research – pathogen assays. They are testing for diseases that can affect humans and his team has found something – an uptick in a certain tropical disease carrier – leptospira – a bacteria which causes Leptospirosis. He says upwards of 30 percent of the rodents they’re screening are carriers and that’s something our public health agencies aren’t registering.

MICHAEL: So we have a whole suite of pathogens that we're looking at, ranging from viruses to bacteria. And what we're finding is that the pathogen loads in our estimates are much higher than what we would have expected. So if you go back into history and look at what people have looked at in rats in particular, one thing stands out, which is leptospira, which is the basis of Leptospirosis.

MICHAEL: It's a pretty widespread disease, particularly in tropical and subtropical cities. In areas like Salvador and Brazil, it's considered a preeminent health concern. In areas like New York and New Orleans, our public health agencies don't register it anymore, largely because it's thought to have declined since the early 1900s. And what we're finding is that leptospira loads across the city are much, much higher than what everybody would have expected them to be.

MICHAEL: if it goes untreated-- so it's readily treatable. It's a bacterial infection, and it can be treated by a broad spectrum antibiotic. But if it goes untreated, it goes unrecognized it can kill you.

MICHAEL: What's unfortunate is that we don't have the public health infrastructure right now to really get at how much of a concern this is. So in areas of the United States where leptospirosis is recognizably prevalent, in particular in Hawaii, public health agencies take preventative measures. For examples, they have signs all across the archipelago that say you could potentially be at risk for contracting Leptospirosis in these areas of concern. So in places like Louisiana where Leptospirosis certainly is present, there is no infrastructure like that.

MICHAEL: There are no precautionary measures that are being taken. It's also something that isn't registered as being a disease of concern. So if somebody were to walk into a hospital who has a leptospira infection it wouldn't necessarily be diagnosed as such. So it's something that's not necessarily prevalent-- of primary concern in health care, particularly in New Orleans. And a lot of that is just again by culture, by virtue. The concern has declined over the years.

MICHAEL: And so from a healthcare perspective it would certainly benefit folks to again recognize that there is this concern and potentially take precautionary measures.

CHARLIE: So, let’s recap…Blum’s 311 data suggests New Orleans rats are more at home…away from humans and his pathogen assays show they are carrying a higher than normal rate of leptospira. How can this data and rat facts help us prepare for future disaster relief tools?

MICHAEL: So from a very fundamental science perspective, what we want to know is how do physioecological systems merge over time. How do they operate? How do they behave? But in real practical terms our intent is to aggregate all the information that we have about rats, develop, put it into a fairly sophisticated mathematical model that is spatially explicit, that maps out effectively onto the New Orleans landscape and have it serve as a decision-making tool.

MICHAEL: So, if the city for example wants to understand how to manage its landscape more effectively either to reduce risk or to increase ecosystem services, they can use this tool to decide whether they want to focus their efforts on one block or another block to redistribute risk or to minimize risk most effectively across the landscape.

CHARLIE: While Blum’s team is down south studying their rodents, what about us East Coast or West Coast dwellers or other urban cities around the world?

MICHAEL: Yeah, so I think the general themes of the study, whether we're talking about rodents or mosquitoes or we're talking about floods or earthquakes, those are generalizable across the United States and certainly across the world. So, the areas where we're finding sort of points of comparison range from New York to Baltimore to Salvador and Brazil to Nepal. In fact, much of what we've done over the last few years has effectively leveraged our work in New Orleans to draw generalizable principles that are broadly applicable.

MICHAEL: So we've worked with folks again in South America, in Southeast Asia, North America. We feel that New Orleans though has its emblematic themes, particularly with respect to post-Katrina recovery. What we feature in many respects is a prelude or a forefront to what people are experiencing worldwide.

CHARLIE: Blum’s research is illustrating how human behaviors affect where rats actually live and the diseases they carry in a post-Katrina New Orleans -- which could provide factual basis for risk perception. His findings may also pave the way for smarter public policies based on data that show where rats are actually living – not on assumptions about where they might be found after a natural disaster has disrupted an urban city.

MICHAEL: So, thankfully, the steps that are taken after disasters happen during the recovery and response phase are pretty effective at reducing outbreak conditions and the likelihood or the possibility of outbreak. So this is something that we're still exploring through meta-analysis, doing some comparisons in the literature and reported cases of outbreaks following disasters. But what it looks like is that, again, we're pretty effective at responding to these concerns.

MICHAEL: But then as that process unfolds or unwinds, there's a concern that some of those initial decisions that are made to reduce the immediate concerns may propagate or delay risk that's only detectable a year or five years, ten years later.

CHARLIE: That was Michael Blum, he’s a molecular ecologist at Tulane University. He is studying rats…where they move in and…what they bring with them after a disaster…His team is laying the groundwork for a potentially powerful mathematical model that will aid in disaster relief.

I’m Charlie Heck, co-editor of Science360’s News Service and co-host of the Super Science Show, at the National Science Foundation.

If you have any questions about this story or suggestions for interviews about super cool NSF-funded science, drop me a line…I promise not to…RAT… you out on air. Email me at editor@science360.gov.