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. 2006 Aug;12(8):1190-6.
doi: 10.3201/eid1708.050841.

Venezuelan equine encephalitis virus transmission and effect on pathogenesis

Darci R Smith  1 , Patricia V Aguilar, Lark L Coffey, Gregory D Gromowski, Eryu Wang, Scott C Weaver
Affiliations

Venezuelan equine encephalitis virus transmission and effect on pathogenesis

Darci R Smith et al. Emerg Infect Dis. 2006 Aug.

Abstract

Quantifying the dose of an arbovirus transmitted by mosquitoes is essential for designing pathogenesis studies simulating natural infection of vertebrates. Titration of saliva collected in vitro from infected mosquitoes may not accurately estimate titers transmitted during blood feeding, and infection by needle injection may affect vertebrate pathogenesis. We compared the amount of Venezuelan equine encephalitis virus collected from the saliva of Aedes taeniorhynchus to the amount injected into a mouse during blood feeding. Less virus was transmitted by mosquitoes in vivo (geometric mean 11 PFU) than was found for comparable times of salivation in vitro (mean saliva titer 74 PFU). We also observed slightly lower early and late viremia titers in mice that were needle injected with 8 PFU, which represents the low end of the in vivo transmission range. No differences in survival were detected, regardless of the dose or infection route.

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Figures

Figure 1
Figure 1
Titers of Venezuelan equine encephalitis virus (VEEV) transmitted in vitro or in vivo by Aedes taeniorhynchus. A, C, and E) Mosquitoes that engorged to completion (depicted by closed symbols). B, D, and F) Mosquitoes who probed but did not engorge (depicted by open symbols). The assay used to determine the virus titer was either cell culture assay (A and B, depicted by squares) or real-time reverse transcription–PCR (C and F) of tail homogenate supernatant (C and D, depicted as triangles) or pellet (E and F, depicted as circles). The last 2 cohorts (G and H) represent VEEV titers in saliva of mosquitoes allowed to salivate for 45 min (G, depicted as +) or for the same range of times (<3 min) required for mosquitoes to engorge completely on mouse tails, repeated in triplicate (H, depicted as ×). Solid horizontal lines indicate means, and horizontal dashed lines indicate detection limits for the assays. Symbols below the dashed lines indicate samples from infected mosquitoes (bodies and legs or wings positive for cytopathic effects) that were below the limit of detection for the assay, and numbers indicate the percentages for these negative samples (column A=36%, B=47%, C=21%, D=33%, E=57%, F=73%, G=3%, and H=13%). *Denotes mice that were bitten by a given mosquito that died.
Figure 2
Figure 2
Amount of Venezuelan equine encephalitis virus transmitted into a mouse tail versus the time required for complete engorgement. Only samples from mosquitoes that completely engorged and transmitted detectable virus were included.
Figure 3
Figure 3
Viremia in mice infected by 1 mosquito bite or intradermally by needle injection with 2 different doses of Venezuelan equine encephalitis virus representing the range of doses delivered during blood feeding (Figure 1). Five animals per cohort were bled at each time point. Error bars indicate standard deviations.
Figure 4
Figure 4
Survival of cohorts of 10 mice infected with Venezuelan equine encephalitis virus either by 1 mosquito bite or by intradermal needle injection with 2 doses representing the range of virus titers delivered during mosquito blood feeding (Figure 1).
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