A framework for the study of zoonotic disease emergence and its drivers: spillover of bat pathogens as a case study

Wood, James L. N.; Leach, Melissa; Waldman, Linda; MacGregor, Hayley; Fooks, Anthony R.; Jones, Kate E.; Restif, Olivier; Dechmann, Dina; Hayman, David T. S.; Baker, Kate S.; Peel, Alison J.; Kamins, Alexandra O.; Fahr, Jakob; Ntiamoa-Baidu, Yaa; Suu-Ire, Richard; Breiman, Robert F.; Epstein, Jonathan H.; Field, Hume E.; Cunningham, Andrew A.

In Bangladesh, where Nipah virus spillover occurs annually [62, 63] , and in Asia, there is a temporal association between bat reproduction and potential zoonotic spillover events [47, 64] . In West Africa, E. helvum bats probably birth and mate during migration [65 -67] , which might be linked to, or even driven by, the nutritional needs of the females and their offspring, but the timing and place of these remain largely unknown [65, 68] . It is possible, therefore, that spillover events occur on the migratory route of this species. Knowledge about migration, time and place of the reproductive cycle in conjunction with the number of animals at any given time and place, and resource availability will provide crucial information about these ecological keystone species, and point to where and when potential spillover to humans should be researched. Alternatively, bats may use migration to escape from areas with high disease load, or lower pathogen prevalence during migration [69] . The ecology and distributions of fruit bats in many countries in which spillover may occur are not very well characterized, particularly quantitatively. This is the case even in Australia, although huge advances have been made there in recent years [47] . The study of zoonotic pathogens has stimulated the study of a number of species, including Pteropus giganteus [70] and Pteropus vampyrus [71] in India, Malaysia and Bangladesh and E. helvum in Ghana [72, 73] . In Australia, however, where Hendra virus spillover could come from any of four fruit bat species, the role of sympatry and cross-species virus transmission in driving spillover has not been elucidated at all [46] . A first necessary focus in many regions is the development of national schemes to locate, count and monitor bat colonies of focal bat species, to determine migratory patterns and to assess the reproductive cycle and efficiency. Quantification of social interactions between bats (e.g. mother-offspring, mating, fighting, allogrooming, etc.) would provide information on possible virus transmission routes. A second essential focus should be to understand feeding behaviour and ecology, as undertaken already in Bangladesh [74] . The use of novel high-resolution GPS data loggers allows detailed and quantitative studies of ranging behaviours of bats and their environmental determinants. Such methods would also underpin the identification of food plants and allow resource use to be quantified through faecal analyses [75] . The importance of fruit bats to the structures and functions of local ecosystems is often very poorly characterized; improving our understanding of this will inform how bats influence ecosystems and how land use change might influence bat populationand consequently infection-dynamics (see below).