Why do bats carry so many diseases?
Bats have a unique immune response which enables them to remain healthy despite carrying viruses that would cause serious disease in people and other mammals. This is likely a side effect of the evolution of flight, which caused bats to develop high metabolic rates and body temperatures up to 41 degrees Celsius. High temperature and metabolic rates can cause DNA damage, and in response bats evolved to have strong DNA repair pathways together with the adaption of flight. This now means bats virus immune response is particularly strong in detecting viruses.
Diseases carried by bats
Bats are reservoirs (long-term hosts) for diseases like Ebola, Marburg virus, rabies and potentially even coronavirus. We are working to better understand the spill over of these diseases to people and other wildlife.
Bats and bugs – understanding viruses in bats
The rate of zoonotic disease emergence from wildlife is increasing, and bats have been identified as the source of many incurable viral diseases of people, often with high case fatality rates. Together with our partners, we are researching the spill over of zoonotic bat viruses in Africa, to better protect bats and people. We are studying the ecology of viral pathogens of known or potential zoonotic risk in fruit bats in West Africa, and human interactions with these bats.
Our collaborative Bats and Bugs project focuses on Lagos bat virus (a type of rabies virus), filoviruses (e.g., Ebola and Marburg viruses) and paramyxoviruses, including henipaviruses. We are exploring the impact of these pathogens on the bats themselves, possible factors influencing their spill-over into people and how these might be enhanced or decreased by human influences on the environment.
Our work with bat viruses
Studying pathogens, such as viruses, in wild bats can be difficult, particularly for bats with large population sizes and for those which fly over large areas. We are in a unique position having maintained a captive breeding colony of the straw-coloured fruit bat (Eidolon helvum) in Ghana since 2010. This is enabling research on the virus infection status of a defined colony along with the infection history of individual bats.
Research over the past year has identified a high incidence of multiple paramyxoviruses, including henipaviruses, in our captive colony. This was unexpected as research on paramyxoviruses in other species suggests that they need very large numbers of animals to infect to persist within a population. Our results indicate that within-host paramyxoviral persistence underlies the role of bats as reservoirs of these viruses.
By collecting under-roost urine every week for an entire year, we investigated possible seasonal patterns of shedding of virus or viral RNA. This research has shown that virus secretion peaked twice in the year, with the greatest peak in July and another in January. Different paramyxoviruses appeared to have different shedding patterns. No association between peaks of virus secretion and birthing season, environmental temperature or humidity was detected. There were no signs of illness in the bats during the year of sample collection, indicating that the viruses they harbour do not cause disease in their natural host.
Having now identified a suite of paramyxoviruses in the captive colony of E. helvum, we are able to modify our laboratory tests to increase their sensitivity of detection for future sample analyses.
Also, we have recently been funded to expand our research to include the investigation of coronaviruses in bats in Ghana and the role of agricultural encroachment and intensification in the zoonotic spill-over of a range of zoonotic viruses carried by bats.
Why do we need to understand bat disease?
Bats are keystone species for ecological function. Fruit bats are important for fruit tree pollination (for example mangos) and aid seed dispersal. Although they have studied in parts of Asia and Australia, the impact fruit bat diseases can have in Africa is less understood.
In some counties in Africa, bats are widely hunted for food, increasing the potential for zoonotic disease transmission. Through understanding the ecology of pathogens in their natural hosts and the drivers of zoonotic spill-over, we’re working to prevent disease emergence in people whilst also conserving bats.
Preventing zoonotic disease
As we encroach further into natural habitats, the interactions between bats and human populations increase; this is especially the case as large populations of fruit bats now live in towns and cities following our encroachment on their natural habitat. This poses new challenges as how best to manage these populations in a sustainable and humane way.
Bat disease research
Our bat disease research is advancing understanding of the ecology of pathogens, such as viruses, in fruit bat populations. This includes understanding how different pathogens persist in their natural hosts, what affect they have on their hosts and how and when they are transmitted.
How connected are different bat populations?
To do this, we use techniques such as radio-telemetry and population genetics. These tell us if bats move between different colonies and, if so, how frequently this occurs. For the species of fruit bat that undergo annual migration, we can detect if the same bats come back to the same place every year.
What do we test African fruit bats for disease?
We capture bats and take small blood samples to look for antibodies that could indicate whether they have been previously exposed to certain pathogens. We also test urine and tissues using molecular (genetic) techniques to identify the types of pathogens present.
How do bats and people interact?
By finding out the risk factors for the spill-over of infection from bats to people, preventative measures can be taken to protect public health while also protecting the bats from persecution.
Recommended further reading to understand bat disease
• The straw-coloured fruit bat (Eidolon helvum) is widespread in sub-Saharan Africa and is widely hunted for bushmeat. It is known to harbour a range of paramyxoviruses, including rubuloviruses and henipaviruses, but the zoonotic potential of these is unknown. In this study, we used under-roost urine collection to further investigate the paramyxovirus diversity and ecology in this colony, which had been closed to contact with wild bats for 10 years at the time of sampling.
Jolma ER, Gibson L, Suu-Ire RD, Fleischer G, Asumah S, Languon S, Restif O, Wood JLN, Cunningham AA. Longitudinal Secretion of Paramyxovirus RNA in the Urine of Straw-Coloured Fruit Bats (Eidolon helvum). Viruses. 2021 Aug 20;13(8):1654. doi: 10.3390/v13081654.
• Recently, African fruit bats with populations that roost in or near urban areas have been shown to harbour a great diversity of paramyxoviruses, posing potential spillover risks to public health. Understanding the circulation of these viruses in their reservoir populations is essential to predict and prevent future emerging diseases. We identified a high incidence of multiple paramyxoviruses in urine samples collected from a closed captive colony of circa 115 straw-coloured fruit bats (Eidolon helvum).
Gibson L, Ribas MP, Kemp J, Restif O, Suu-Ire RD, Wood JLN, Cunningham AA. Persistence of Multiple Paramyxoviruses in a Closed Captive Colony of Fruit Bats (Eidolon helvum). Viruses. 2021 Aug 20;13(8):1659. doi: 10.3390/v13081659.
• We aimed to document the extent of henipa- and filovirus exposure among Malagasy fruit bats, explore seasonality in seroprevalence and serostatus in these bat populations and compare mechanistic hypotheses for possible transmission dynamics underlying these data. We amassed and analysed a unique dataset documenting longitudinal serological henipa- and filovirus dynamics in three Madagascar fruit bat species.
Brook CE, Ranaivoson HC, Broder CC, Cunningham AA, Héraud JM, Peel AJ, Gibson L, Wood JLN, Metcalf CJ, Dobson AP. Disentangling serology to elucidate henipa- and filovirus transmission in Madagascar fruit bats. J Anim Ecol. 2019
• Pathogen circulation among reservoir hosts is a precondition for zoonotic spillover. Unlike the acute, high morbidity infections typical in spillover hosts, infected reservoir hosts often exhibit low morbidity and mortality. Although it has been proposed that reservoir host infections may be persistent with recurrent episodes of shedding, direct evidence is often lacking.
We find that reinfection is necessary to explain observed dynamics; that acute infectious periods may be very short (hours to days); that immunity, if present, lasts about 1–2 years; and that recurring latent infection is likely.
Glennon, E. E., D. J. Becker, A. J. Peel, R. Garnier, R. D. Suu-Ire, L. Gibson, D. T. S. Hayman, J. L. N. Wood, A. A. Cunningham, R. K. Plowright, and O. Restif. 2019. What Is Stirring in the Reservoir? Modelling Mechanisms of Henipavirus Circulation in Fruit Bat Hosts. Phil Trans B. 2019