A Virus Bottleneck

Bottleneck Every year I get excitied and rant at my virology students about how amazing it is that a virus can have more than more host, i.e. for viruses which undergo propagative transmission, replicating in both the “host” and the “vector”. For the most part, the students humour me, trying to pretend it’s not happening. When we reach that point in the course this year, I suspect arms will get waved wildly in the direction of this paper.

“In summary, there must be a complicated interplay between the various evolutionary processes to give rise to the viral populations observed in nature. Even within the mosquito, different arbovirus mutations may confer different advantages in critical organs such as the midgut and the salivary glands. In addition, the influence of vertebrate hosts on the maintenance of arbovirus diversity has yet to be determined.”

 

Vector-Borne Transmission Imposes a Severe Bottleneck on an RNA Virus Population. (2012) PLoS Pathog 8(9): e1002897. doi:10.1371/journal.ppat.1002897
The ability of arboviruses to perpetuate in nature given that they must infect two disparate hosts (the mosquito vector and the vertebrate host) remains a mystery. We studied how viral genetic diversity is impacted by the dual host transmission cycle. Our studies of an enzootic cycle using Venezuelan equine encephalitis virus (VEEV) and its natural mosquito, Culex taeniopus, revealed the stages of infection that result in a viral population bottleneck. Using a set of marked VEEV clones and repeated sampling at various time points following C. taeniopus infection, we determined the number of clones in various mosquito tissues culminating in transmission. Bottlenecks were identified but the stage of occurrence was dependent on the dose that initiated infection. Understanding the points at which mosquito-borne viruses are constrained will shed light on the ways in which virus diversity varies, leading to selection of mutants that may result in host range changes or alterations in virulence.

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