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Investigating the ecology of a deadly virus

February 22, 2020

Micah Hahn:
The way the virus gets from bats into people in Bangladesh revolves around this process
of collecting sap from date palm trees. And it’s a very common practice in Bangladesh
very similar to the way we tap maple syrup in Wisconsin. The way that it works is a sap
collector will climb up a date palm tree, shave off part of the bark, and then he hangs
up a clay pot to collect the sap overnight. But at nighttime these bats are foraging and
looking for sap and nectar to eat. And when they see this sweet sticky stuff coming out
of a date palm tree, they lick the bark or stick their head into the pot. If one of these
bats is infected with the virus, they transmit the virus into the date palm sap. And the
sap collector will then take this to the market and sell it by the glass. And if you drink
some sap that has been contaminated with the virus, you can become infected yourself. I went to Bangladesh to study the roosting habitats of these fruit bats to see if we could understand how that relates to where we have seen human Nipah virus cases. All of the human Nipah
virus cases in Bangladesh have occurred in the Northwest or central part of the country in this area
that we now call the Nipah belt. Given that we think these bats live throughout the country
and that this practice of sap collection happens throughout Bangladesh, why are we seeing this
cluster of human Nipah virus cases? We were interested in the broad ecological aspects
of Nipah virus. So rather than looking at individual Nipah case patients, we were looking
at the villages and the environment around villages in areas where we have seen outbreaks
and in areas where we haven’t. So the focus of my research was to look at the roosting
habitats of these fruit bats. I found that inside the Nipah belt, the landscape is very
different than the rest of the country. For example, inside the Nipah belt there is less
forest cover, and the forest that is there is much patchier. You would likely see clumps
of forest broken up by agricultural land or homesteads. Whereas in other parts of the
country you would be likely to find contiguous jungle areas. I also found that the human
population density is much higher in the Nipah belt. Interestingly we found that there are
more bat roosts inside the Nipah belt compared to the rest of the country. So in these areas
there is going to be more interaction between bats and people. Likely they are going to
be eating out of the same fruit trees, or bats are going to be running into date palm
sap containers, for example. Which then increases Nipah transmission from bats to people. One
aspect of this study was to hang up infrared cameras to watch the date palm containers
at night to try to understand how the bats are feeding. When we were hanging the cameras
we always had a lot of spectators and they were really curious to see what we were doing
in the village and what all this equipment was. It was really an unexpected education
campaign because it’s one thing to say to someone, ‘This is what Nipah virus is and
this is how it occurs once the bats are drinking out of your date palm sap containers.’ But
it’s another thing to hang a camera with everyone watching. Then take it down the next morning
and say this is what happened in your backyard last night. And for them to actually see photographs
of these bats drinking out of their sap containers. They were astounded and immediately wanted
to know how they could protect their sap containers to keep the bats out. One outcome of this
research is that hopefully we’ll be able to target high-risk areas where we are likely
to see spillover from bats to people, causing more human Nipah virus cases. If we know where
these high-risk areas are, we can target our surveillance and our education campaigns.
The Nelson Institute was a great place to do my research. The Environment and Resources
program was presented as this really flexible program where you could sort of build your
own major, and that’s exactly what I did. I probably took classes at seven different
departments on campus. Applying for fellowships and postdocs for after graduate school, I
talk about how I did this interdisciplinary research, and about how I’m both an epidemiologist
and an ecologist. And I think that makes me unique in the field of public health and environmental
public health. And I don’t think I could have received that training, at least as easily,
at any other university.

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