49 - What makes a particular vertebrate an important amplifying host?

In nature, mosquito-borne arboviruses cycle from viremic vertebrate hosts to appropriate mosquito vectors and back again to immunologically naïve vertebrate hosts.  But there is a certain amount of specificity to these cycles.  Just as not every mosquito species can transmit every arbovirus (thankfully), not every vertebrate species can serve as good amplifying hosts for every arbovirus.  There are several behavioral and population-based attributes of vertebrate species that can contribute to their status as amplifying hosts. These include such things as; host attractiveness to mosquitoes, defensive behavior against mosquito attack, the relative abundance of hosts, and the reproductive turnover of hosts (i.e., recruitment of new, non-immune individuals).  But underlying all of this is the innate susceptibility of the vertebrate to an arbovirus.  This has traditionally been measured as the intensity and duration of viremia (i.e., virus concentration in the blood) that a host species experiences upon infection.  For arbovirus transmission cycles involving multiple host species (e.g., West Nile virus), the relative contribution of a host species traditionally has been inferred from its viremia  – that is, species developing high viremias are more important amplifying hosts than species developing low viremia.  Intuitively, this makes sense and the idea that higher viremia invariably results in higher infectiousness to mosquitoes has led to a concept known as “host competency”.  But recent studies have suggested that host infectiousness to mosquitoes may not always be linked just to host viremia.  This presentation will examine our current understanding of “host competency” and will discusses recent findings that may improve that understanding.