Vector-Borne Pathogen Spread Through Ticks on Migratory Birds: A Probabilistic Spatial Risk Model for South-Western Europe

Tick-borne pathogens can spread easily through the movements of infested birds. An important example is viruses that pose a threat to humans and that are carried in Hyalomma ticks that move from Africa into south-western Europe. This study evaluates the probability of arrival of migrating birds from Africa into Spain and the environmental suitability of different regions of Spain for the survival of tick stages introduced by these birds. This evaluation produced a spatial risk index measuring the probability that foreign tick populations will survive in the target area. Periods of highest risk were observed for large areas of Spain, from the second fortnight of April to the second fortnight of May. Although birds may arrive as early as January and massive migrations may take place in March, the environmental suitability for Hyalomma marginatum ticks is low in these periods and high mortality of the spread stages (nymphs) is expected. This study introduces new methods of objective analysis based on spatial and process-driven models for both ticks and hosts and critically evaluates the usefulness of spatial spreading methods for assessing the risk of tick-borne pathogens.