The elephant in the room; evaluating parasite infection with applications for management in an endangered host.

Abstract

In natural populations parasites are aggregated, with the majority of parasites found in few, specific hosts, whereas the majority of hosts harbour low or no parasite burdens. Previous research has outlined certain demographic groups, for example juveniles and males, as being carriers of higher parasite burdens compared to their conspecific counterparts. However many such studies are based on cross-sectional observations, or focus on findings from laboratory, captive or short-lived systems. While valuable, this skew in the literature leaves a gap in our understanding, namely that of how host-parasite dynamics operate in exotic or endangered host species, or host populations which exist in natural conditions. Consequently, there is comparatively little information concerning how infection dynamics operate in endangered or declining hosts, to aid management and welfare practices. The Asian elephant (Elephas maximus) is an endangered, declining species, which now exists in a fragmented populations in an area spanning approximately 5% of their former total range (IUCN 2018). Myanmar houses the largest captive population of Asian elephants in the world, with over half of this number comprising of semi-captive timber elephants, who are utilised in logging camps throughout the country. Parasites, such as gastro-intestinal nematodes, have been a recognised health threat to the working elephants of Myanmar for over a century (Evans1910). However, few studies have assessed infection dynamics in this endangered host system. By utilizing both a multigenerational database and current measures of infection for ~300 elephant hosts, we determined host-specific variation in re-infection dynamics in response to anthelmintic treatment. First, we tested the effectiveness of treatment in decreasing nematode burden within 35 days of administration. Second, we investigated longitudinal changes in nematode burdens for different elephant demographics, following de-worming by anthelmintics, to establish variation in re-infection rates. Finally, we determine associations of treatment on host condition, using body weight as a proxy. Our results provide insights to nematode burden re-establishment for specific host demographics, in a little studied host system. As such, our findings have broader applications to the management and welfare of not only other Asian elephant populations, but also other captive, managed and endangered host taxa.

The IUCN Red List of Threatened Species. Version 2017-3. . Downloaded on 30 January 2018.

Evans, G.H. (1910) Elephants and Their Diseases: A Treatise on Elephants. Superintendent, Government Printing, Burma, Rangoon, Burma.