Bat Endoparasites: A UK Perspective

Abstract

Studies have shown that bats are infected with a rich community of endoparasites. However, detailed investigations are lacking; not least because of the challenges of working with hosts that are protected by legislation. Below, we review the status of bat endoparasite studies in the UK, giving due consideration to a significant body of classical parasitological investigations on haematozoa (trypanosomes, the piroplasm Babesia vesperuginis and the haemosporidian Polychromophilus murinus) carried out in the mid-1980s on almost 500 hosts and encompassing 12 of the 17 bat species known to breed in the UK. Of these parasites, only B. vesperuginis-infected bats showed any adverse health impacts, including elevated reticulocyte and white blood cell counts, reduced haemoglobin levels, haemoglobinuria and splenomegaly. More recently, molecular-based analyses of UK bat haematozoa have contributed not only to enriching survey data but also importantly to a wider understanding of evolutionary relationships amongst parasites, which in turn has provided insight into historic movements of the hosts. We also discuss gastrointestinal parasite infections and highlight the lack of published studies on UK bat coccidians and helminths. As such, morphological and molecular analyses carried out in our laboratory, on a population of pipistrelle bats in South Lancashire and Greater Manchester, are providing baseline data on these infections in UK bats. With regard to helminths, we find that pipistrelle bats are commonly infected with digenean trematodes (prevalence = 76 %; mean abundance = 48.2 ± 7), particularly lecithodendriids (e.g. Lecithodendrium linstowi). Moreover, helminth infections were significantly more aggregated and also less abundant in male bats compared to females, an interesting and perhaps surprising parasite response to the host sex hormones. DNA sequencing of the 28S rRNA gene of representative lecithodendriid specimens has offered new insight into evolutionary relationships amongst the Lecithodendriidae, specifically, separating a controversial clade between L. linstowi and Prosthodendrium hurkovaae. Finally, we highlight recent work that utilises PCR-based detection to implicate bats as potentially important reservoir hosts of the apicomplexan Toxoplasma gondii (prevalence = 10 %).

With respect to bat health and disease, although endoparasite infections have been linked to specific pathologies (e.g. splenomegaly), compelling recent evidence suggests that the overall rate of severe disease is low (10 %) and that the mortality rate, due primarily to endoparasite infection, is minimal (0.5 %). As such, the relationship between bats and their endoparasites is probably evolutionarily ancient and reflective of a healthy ecosystem.

Importantly, bat endoparasite research, both in the UK and elsewhere, is contributing to a greater understanding of parasite biodiversity and wildlife health and disease. Significant challenges remain; not least understanding the community ecology of bat parasites and how these infections impact upon other important infectious diseases of bats (viral, bacterial and fungal). Progress will be dependent upon multidisciplinary approaches that encompass the expertise of many individuals including parasitologists, bat biologists, veterinarians and volunteer members of bat conservation groups.