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Investigation of Biological Factors Contributing to Individual Variation in Viral Titer after Oral Infection of Aedes aegypti Mosquitoes by Sindbis Virus.

ABSTRACT: The mechanisms involved in determining arbovirus vector competence, or the ability of an arbovirus to infect and be transmitted by an arthropod vector, are still incompletely understood. It is well known that vector competence for a particular arbovirus can vary widely among different populations of a mosquito species, which is generally attributed to genetic differences between populations. What is less understood is the considerable variability (up to several logs) that is routinely observed in the virus titer between individual mosquitoes in a single experiment, even in mosquitoes from highly inbred lines. This extreme degree of variation in the virus titer between individual mosquitoes has been largely ignored in past studies. We investigated which biological factors can affect titer variation between individual mosquitoes of a laboratory strain of Aedes aegypti, the Orlando strain, after Sindbis virus infection. Greater titer variation was observed after oral versus intrathoracic infection, suggesting that the midgut barrier contributes to titer variability. Among the other factors tested, only the length of the incubation period affected the degree of titer variability, while virus strain, mosquito strain, mosquito age, mosquito weight, amount of blood ingested, and virus concentration in the blood meal had no discernible effect. We also observed differences in culture adaptability and in the ability to orally infect mosquitoes between virus populations obtained from low and high titer mosquitoes, suggesting that founder effects may affect the virus titer in individual mosquitoes, although other explanations also remain possible.

SUBMITTER: Hodoameda P

PROVIDER: S-EPMC8780610 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Arboviruses are transmitted by specific vectors, and the reasons for this specificity are not fully understood. One contributing factor is the existence of tissue barriers within the vector such as the midgut escape barrier. We used microRNA (miRNA) targeting of Sindbis virus (SINV) to study how replication in midgut cells contributes to overcoming this barrier in the mosquito Aedes aegypti. SINV constructs were designed to be attenuated specifically in midgut cells by inserting binding sites for midgut-specific miRNAs into either the 3' untranslated region (MRE3'miRT) or the structural open reading frame (MRE-ORFmiRT) of the SINV genome. Both miRNA-targeted viruses replicated less efficiently than control viruses in the presence of these miRNAs. When mosquitoes were given infectious blood meals containing miRNA-targeted viruses, only around 20% (MRE3'miRT) or 40% (MRE-ORFmiRT) of mosquitoes developed disseminated infection. In contrast, dissemination occurred in almost all mosquitoes fed control viruses. Deep sequencing of virus populations from individual mosquitoes ruled out selection for mutations in the inserted target sequences as the cause for dissemination in these mosquitoes. In mosquitoes that became infected with miRNA-targeted viruses, titers were equivalent to those of mosquitoes infected with control virus in both the midgut and the carcass, and there was no evidence of a threshold titer necessary for dissemination. Instead, it appeared that if infection was successfully established in the midgut, replication and dissemination were largely normal. Our results support the hypothesis that replication is an important factor in allowing SINV to overcome the midgut escape barrier but hint that other factors are also likely involved. IMPORTANCE When a mosquito ingests an arbovirus during a blood meal, the arbovirus must escape from the midgut of the vector and infect the salivary glands in order to be transmitted to a new host. We used tissue-specific miRNA targeting to examine the requirement for Sindbis virus (SINV) to replicate in midgut epithelium in order to cause disseminated infection in the mosquito Aedes aegypti. Our results indicate that specifically reducing the ability of SINV to replicate in the mosquito midgut reduces its overall ability to establish infection in the mosquito, but if infection is established, replication and dissemination occur normally. These results are consistent with an importance for replication in the midgut epithelium in aiding arboviruses in crossing the midgut barrier.

Dataset Information

Investigation of Biological Factors Contributing to Individual Variation in Viral Titer after Oral Infection of Aedes aegypti Mosquitoes by Sindbis Virus.

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