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Cambridge Infectious Diseases

An Interdisciplinary Research Centre at the University of Cambridge

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Bats, Date Palms and Emerging Diseases

PI Portraits: Professor James Wood

I spoke to Professor James Wood (Veterinary Medicine) to discuss the important relationship between bats and disease, and the research currently undertaken by his group.

How did you get into working with bats?

Pure serendipity. I had thought it was mad to work on wildlife disease epidemiology because it is very difficult to catch enough of the species you are interested in to make it numerically interesting, and then they try to bite you. However, through the Cambridge Infectious Disease Consortium (CIDC) we identified a Veterinary Fellow, David Hayman, who was insistent that he wanted to do work in this field, Andrew Cunningham (Institute of Zoology) came up with a suitable project, and we found some pilot funding to send David to Ghana.  I expected him to obtain samples from maybe 20 bats and not find anything of interest, but he came back with samples from 300-400 bats and we found lots.  Fortuitously, this happened at a time when there was increasing realisation of the importance of bats as carriers of zoonotic pathogens and so more funding was available to pursue this area of research.Bats

So what are the projects you’ve been working on recently?

I am interested in emerging diseases of humans and animals, for the simple reason that if we can understand why they are emerging we can do something to reduce rate/significance of emergence. At the moment we are examining the specific mechanisms of viral persistence in bat populations while also trying to get more general insight into the importance of bats in disease emergence – as well as studying spillover itself.

We are also examining anthropogenic drivers for disease emergence. Human behaviour such as hunting or butchery can make a huge difference to the likelihood of a pathogen spilling into humans. Alexandra Kamins, a PhD student in our lab, has discovered through field surveys that more than 100,000 bats are killed, shipped and sold as food just in Accra, Ghana every year. Simple behavioural changes can be the most effective means of avoiding pathogen spillovers, although often though most difficult to encourage (especially when driven by poverty). One particularly nice example (although not one we’ve been involved with ourselves) of how simple behavioural change can affect pathogen spillover is that of date palm tappers in Bangladesh. We all live closely with bats because they live in our roofs, but most people have no direct contact. Some, such as guano harvesters (bat guano is a rich source of nitrogen for fertiliser), bat hunters, and butchers have a huge amount of contact with bats and bat faeces. We also want to consider indirect transmission- the bats that we work on have potentially nasty paramyxoviruses in their urine, and urinate on probably thousands of people across the continent daily. Fruit bats said to eat roughly their body weight in fruit every day, which produces not only an effective splat, but a lot of urine. What the human factors associated with living or working around them?

We recently published a set of practical guidelines to facilitate the integration of mathematical models in infection ecology—what we call model guided field work. Too often field work is done, published and then models fitted as an afterthought, so studies are not joined up. Model guided field work is essentially an iterative process of modelling, whereby you review what you know, identify a question, develop models to describe the system you are looking at, use the models to identify which bits of data you really need, collect the data, refit the model, and then re-challenge it iteratively until you have something that holistically captures the system.

Datepalm sap and Nipah virusClimbing a date palm in Tozeur Oasis

Date palm sap is a very popular sugary drink in Bangladesh, particularly with children. It’s harvested in a similar fashion to rubber- a cut is made in the palm trunk, and over 1-3 days, the stream of sap is collected in a pot held below the cut. It is also very popular with the local fruit bats, which will come and drink from, salivate and urinate in the stream. Fruit bats are a known reservoir of Nipah virus, and several outbreaks have been directly associated with date palm sap.

However, Steve Luby and colleagues in Bangladesh devised a cheap means of stopping bats getting at the sap – a jute skirt. Jute grows everywhere and can be bound together into a screen with jute string. Thus, for next to nothing it is possible to stop bats contaminating the sap, making it easier to sell, and prevent Nipah virus spillover. There has been reasonable uptake of these screens where they have been promoted, but it remains to be seen how sustainable use will be. Those who sell date palm sap are among the poorest in Bangladesh (as are bat hunters), and so any intervention needs to be more or less free to ensure uptake.

What’s exciting at the moment?

So far we have been focusing onthe most common fruit bat in Sub Saharan Africa. They live in roosts of up to 10 million across the continent, and although it has been known that individual bats can fly several thousand kilometres, we expected some degree of genetic variation between bats found in e.g. Senegal and Malawi. However, Ali Peel’s genetic studies based on microsatellites and mitochondrial genes have found no isolation by distance whatsoever, which I find amazing: there is enough mixing across the whole continent to consider it a single population, and this has important implications for virus circulation. Hugely exciting is a paper that came out recently in PLoS ONE and reported henipavirus infection within an isolated subspecies of fruit bat living on a remote island off the African coast. It had previously been thought that henipaviruses could only persist in large bat populations. However, this particular subspecies has a population of no more than two thousand, and yet we have found antibodies against henipaviruses. This means we have to rewrite our understanding of likely mechanisms of viral persistence in bats. Fortunately we have received some support for Alison’s postdoctoral studies in this area from the Newton Trust.

Another area we are just beginning to get data on is the massive diversity of paramyxoviruses in bat urine—exciting results are coming from Kate Baker’s Wellcome fellowship project. There is increasing evidence, based on the amount of diversity for coronaviruses, paramyxoviruses, and astroviruses, that the vast majority of these viruses found in other species may well have originated in bats. More coronavirus diversity has been found in one bat cave in Hong Kong than across all previous coronaviruses, suggesting that it is likely that bats have been the major reservoirs for this whole family of viruses. Other studies, collaborating with Colleen Webb and others at Colorado State University, are examining macroecological factors associated with bats that appear to make them different from other species such as rodents. Rodents tend not to share niches - rats and mice do not generally live in the same holes - whereas bats live in vast numbers in close contact with other species. It may well be that some of these cave systems are very important, or a general overlap of bat distributions around the world. This is interesting at many different levels.

ANTIGONE logoWe are involved in the EU funded ANTIGONE (ANTIcipating the Global Onset of Novel Epidemics) programme, which contains a bat disease emergence programme. This will allow us to start addressing some specific questions about rabies and lyssavirus in African fruit bats. We are also part of a new £3.2m programme with the Institute of Development Studies which will look at population level infection dynamics of henipaviruses in Ghanaian fruit bats and at bat-human interactions in West Africa; and the RAPIDD programme (with Colleen Webb) to look at small mammals, including bat diseases.

One of the most important aspects of our research has been our fantastic collaborators in Ghana, forming part of the nascent ‘Cambridge in Africa’ programme. Some African scientific infrastructure is rather poorly supported, so this type of capacity building work is really important. We have recently been given $1m from Alborada trust to support African Fellowships and $1.2M from Carnegie Corporation. There are so many fantastic academics lacking resources there, so it’s a fantastic opportunity to support them while doing some really interesting research.

What do you foresee to be the greatest challenges in your area of research?

Some of the greatest challenges are going to be working out how we achieve sustainability of ecosystems that bats live in to prevent them from being wiped out. Bats are critically important in maintaining biodiversity and ecosystems.  Insectivorous bats eat tons of insects every night and fruit bats are vital for pollination of tropical hardwoods and seed dispersal. We need to sustain ecosystems whilst at the same time preventing spillover of infectious disease. We also need to balance addressing what might be a local risk against global challenges. Given the encroachment of people and bats into each other’s communities, the risks may be increasing. It is not just people encroaching into forests; it is also large colonies of bats living closer to people.

Advice to early career researchers?
When in doubt, jump (but don’t do as I have done and try to land feet first!).


---Anna Davies, 2012