The Relative Contributions of Transovarial and Transstadial Transmission to the Maintenance of Tick-Borne Diseases
It is a common misconception that, because of the frequently observed low coefficient of transovarial transmission of many tick-borne diseases, this transmission route contributes very little to the maintenance of the diseases (inter alia Porco, 1991). A simple model, that includes the important epidemiological parameters of tick reproduction and mortality rates, shows that the potential contribution of transovarial transmission is greater than that of transstadial transmission, even when. the transmission coefficient of the former is less than 10% of that of the latter. The actual contribution will depend on the specific vector/host relationships for each tick-borne disease, and the susceptibility to the disease of the host species for each tick stage. The example presented here concerns the maintenance of Lyme disease in wild vertebrate populations.
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