Challenging the dogma of the ‘Island Syndrome’: a study of helminth parasites of feral cats and black rats on Christmas Island

ABSTRACT

Many island ecosystems are exposed to ecological threats through invasive species and the parasites they harbour. Parasites can impact endemic island populations whether they are stable populations or ones already in decline. The ‘Island Syndrome’ hypothesis proposes that richness and diversity of introduced parasites differ from mainland populations with lower parasite species diversity on islands due to the founder effect. To examine the role of ‘Island Syndrome’ and impacts for faunal and human communities on a tropical island, helminth parasites were identified from feral cats (Felis catus) (n = 66) and black rats (Rattus rattus) (n = 101) on Christmas Island. Sixty-one (92 per cent) of cats and 85 (84 per cent) of rats harboured one or more helminth species with total infra-community richness (TICR) ranging over zero to six species in cats and zero to seven species in rats, including species of zoonotic significance (Angiostrongylus cantonensis, Toxocara cati, Ancylostoma braziliense, Taenia taeniaeformis, Moniliformis moniliformis and Hymenolepis nana). High parasite prevalence and TICR were expected in island populations; however, high parasite richness in cats and rats on Christmas Island was counter to the ‘Island Syndrome’. These results suggest that introduced cats and rats may be responsible for maintaining an increased parasitological threat to fauna and human communities in certain ecosystems.

KEYWORDS:

• One Health
• Island Syndrome
• parasites
• feral cats
• black rats
• Christmas Island

Acknowledgements

We would like to acknowledge sample collection by Neil Hamilton from DPAW, Genevieve Hayes and Bing Low for their help on Christmas Island, the staff of Christmas Island National Parks for their assistance, and the Department of Immigration and Citizenship which kindly provided accommodation. The authors would like to thank for their financial support of this project the Shire of Christmas Island (SOCI) as the auspice for this funding and CINP as the project manager. We would also like to thank SERCO for their in-kind support during the project. We acknowledge the support received from Christmas Island Phosphates as well as the support and encouragement from the community of Christmas Island. The authors would also like to thank Aileen Elliott and Russ Hobbs for their assistance in parasite identification.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Murdoch University, the Department of Infrastructure and Regional Development (formerly, Department of Regional Australia, Local Government, Arts and Sport).