Abstract
Because of their relative simplicity and the barriers to gene flow, islands are ideal systems to study the distribution of biodiversity. However, the knowledge that can be extracted from this peculiar ecosystem regarding epidemiology of economically relevant diseases has not been widely addressed. We used information available in the scientific literature for 10 old world islands or archipelagos and original data on Sicily to gain new insights into the epidemiology of the Mycobacterium tuberculosis complex (MTC). We explored three nonexclusive working hypotheses on the processes modulating bovine tuberculosis (bTB) herd prevalence in cattle and MTC strain diversity: insularity, hosts and trade. Results suggest that bTB herd prevalence was positively correlated with island size, the presence of wild hosts, and the number of imported cattle, but neither with isolation nor with cattle density. MTC strain diversity was positively related with cattle bTB prevalence, presence of wild hosts and the number of imported cattle, but not with island size, isolation, and cattle density. The three most common spoligotype patterns coincided between Sicily and mainland Italy. However in Sicily, these common patterns showed a clearer dominance than on the Italian mainland, and seven of 19 patterns (37%) found in Sicily had not been reported from continental Italy. Strain patterns were not spatially clustered in Sicily. We were able to infer several aspects of MTC epidemiology and control in islands and thus in fragmented host and pathogen populations. Our results point out the relevance of the intensity of the cattle commercial networks in the epidemiology of MTC, and suggest that eradication will prove more difficult with increasing size of the island and its environmental complexity, mainly in terms of the diversity of suitable domestic and wild MTC hosts.
Highlights
Island ecology is different from that of mainland systems
By combining information available from the literature on old world islands with original information on Sicily, we were able to infer several aspects of Mycobacterium tuberculosis complex (MTC) epidemiology and control in fragmented pathogen populations. This manuscript should be understood as an attempt of shortening distances between epidemiology and biogeography under the general aim of contributing to the study of animal health from an interdisciplinary perspective [47,48]
The fact that several small islands are M. bovis free could represent an example of the decreasing species survival as island size decreases [49]
Summary
In the seminal work of MacArthur and Wilson [1] the main ecological peculiarities of islands were compiled and put in a biogeographical context. This was the starting point for the development of island biogeography [2]. Communities of parasites–in a broad sense [8]–were studied in the analytical framework of island biogeography Most of these studies were focused on the co-evolution in the parasitehost/s systems [9], parasite distribution patterns and assemblages [10,11,12], and on the parasite traits that prevail in island ecosystems [13]. To our best knowledge, the epidemiology of economically relevant diseases on geographic islands and the new insights that can be extracted from this peculiar ecosystem has not been addressed in detail
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