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Parasite evolution on islands: Socotra reptiles and their parasites as a model study

Final Report Summary - PARIS (Parasite evolution on islands: Socotra reptiles and their parasites as a model study)


Island faunas offer ideal models to explore the evolutionary ecology and epizootiology of parasite assemblages. Island reptiles have been long considered model organisms for evolutionary studies, yet little work has been done on their parasites, despite important conservation and epidemiological implications. The Balearic archipelago (NE Mediterranean) is a popular tourist hotspot and herein the impact of human activities and biological invasions are of important concern for wildlife conservation and the emergence of infectious diseases. However, we know very little about the circulation of zoonoses in the endemic fauna of these islands. The general aim of the project was to investigate spatiotemporal dynamics of infection of pathogens circulating in reptile populations, to evaluate the effects on hosts, as well as to investigate their transmission routes in order to evaluate the risk of spill over to other wildlife species, domestic animals, and potentially humans. To answer this question we focused in a pair of endemic lizards, Podarcis lilfordii and P. pytiutensis, which are closely related, very abundant and widely distributed species in the Balearics, and so ideal systems where to investigate the disease ecology of parasitic infections. We first characterized the parasites circulating in these hosts in multiple islands across the Balearics. We found various species of haemoparasites including Hepatozoon and Eimeria, but no record of Plasmodium malaria parasites. Of importance, we detected enterobacteria of the genus Salmonella circulating in these two lizards. We are also now screening for the presence of malaria parasites of the genus Plasmodium in the mosquitoes as well as mosquito-borne flaviruses. We then went on to investigate spatiotemporal patterns of infection. For Hepatozoon we found that while prevalence was high and persistent, intensity of infection varied temporally across years and spatially among geographic locations. In the case of Salmonella, we found clear differences in prevalence between islands and localities. Second, we investigated the effects of parasite infection on host immunity and body condition. For Hepatozoon some host detrimental effects were apparent at the level of humoral immune responses. Finally, this project aimed to add insights into bridges between the various compartments for the circulation of these pathogens.

For the food-borne bacterial pathogens isolated from reptiles, Salmonella spp., on-going analyses based on multilocus sequence typing, serotyping and antibiotic susceptibility testing; investigate the pathogenicity and assign the source for transmission by comparison with global public databases. Related to the vector-borne transmitted pathogens, we found high diversity of mosquitoes and identified potential bridges for transmission between reptiles and other wildlife based on blood-meal analyses of vectors. Overall, our results have important conservation implications given the high prevalence and abundance of the various parasites examined on the lizards, but also because of the bridge vectors and so the potential risk of spill over to other host species. More importantly, this study reveals for the first time the circulation of Salmonella enterobacteria in reptiles in the Balearic archipelago. Given the high abundance and distribution of the host species and the frequent contact with humans, our findings have potential implications for public health.

Keywords: Islands, reptile parasites, Hepatozoon, Plasmodium, Salmonella, mosquito, detection, infection, epizootiology, transmission networks.