Abstract
Vector-borne diseases represent a major public health concern in most tropical and subtropical areas, and an emerging threat for more developed countries. Our understanding of the ecology, evolution and control of these diseases relies predominantly on theory and data on pathogen transmission in large self-sustaining ‘source’ populations of vectors representative of highly endemic areas. However, there are numerous places where environmental conditions are less favourable to vector populations, but where immigration allows them to persist. We built an epidemiological model to investigate the dynamics of six major human vector borne-diseases in such non self-sustaining ‘sink’ vector populations. The model was parameterized through a review of the literature, and we performed extensive sensitivity analysis to look at the emergence and prevalence of the pathogen that could be encountered in these populations. Despite the low vector abundance in typical sink populations, all six human diseases were able to spread in 15–55% of cases after accidental introduction. The rate of spread was much more strongly influenced by vector longevity, immigration and feeding rates, than by transmission and virulence of the pathogen. Prevalence in humans remained lower than 5% for dengue, leishmaniasis and Japanese encephalitis, but substantially higher for diseases with longer duration of infection; malaria and the American and African trypanosomiasis. Vector-related parameters were again the key factors, although their influence was lower than on pathogen emergence. Our results emphasize the need for ecology and evolution to be thought in the context of metapopulations made of a mosaic of sink and source habitats, and to design vector control program not only targeting areas of high vector density, but working at a larger spatial scale.
Highlights
Vector-borne diseases represent one of the biggest challenges to the current and future human wellbeing [1,2]
Human Vector-borne Diseases We considered three diseases with only human hosts; malaria (MAL), dengue (DEN), and the Gambian form of human African trypanosomiasis (HAT), which all together affect over 250 millions people and kill around 900,000 humans every year [4,5,7]
Sink Vector Populations The stability analysis of our model confirmed that the two epidemiological situations presented in introduction, whereby pathogens are introduced by immigrating vectors, or independently of vector immigration, are very different from a dynamical system point of view
Summary
Vector-borne diseases represent one of the biggest challenges to the current and future human wellbeing [1,2]. The percentage distribution of IH individuals remains virtually the same as when no immigrant is infectious (figure 3), but the transmission of the pathogen has increased since the proportion of cases where more than 5% of individuals are ‘recovered’ raises from 34% to 74%. ‘infectious’ individuals, is not significantly higher when some immigrants are infectious, the circulation of the pathogens in human hosts has been increased. This suggests that the within-host dynamics of the pathogen plays a critical role in determining the prevalence of infection for these diseases. The prevalence of individuals affected by HAT or CD, i.e. both ‘infectious’ and ‘recovered’ individuals, increased significantly when some immigrants are infectious. Compensating for this low probability, by introducing already infectious vectors, strongly facilitates the spread of the disease
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