Background: Humans are the primary hosts of dengue viruses (DENV). However, sylvatic cycles of transmission can occur among non-human primates and human encroachment into forested regions can be a source of emergence of new strains such as the highly divergent and sylvatic strain of DENV2, QML22, recovered from a dengue fever patient returning to Australia from Borneo. The objective of the present study was to evaluate the vector competence of Australian Aedes aegypti (A. aegypti) mosquitoes for this virus.
Methods: Four day old mosquitoes from two strains of A. aegypti from Queensland, Australia, were feed a meal of sheep blood containing 10 8 50% cell culture infectious dose per ml (CCID 50 /ml) of either QML22 or an epidemic strain of DENV serotype 2 (QML16) isolated from a dengue fever patient in Australia in 2015. Mosquitoes were maintained at 28°C, 75% relative humidity and sampled at 7, 10 and 14 days post-infection (DPI). Live virions in mosquito bodies (abdomen/thorax), legs and wings and saliva expectorates from individual mosquitoes were quantified using a Cell Culture Enzyme-linked Immunosorbant Assay (CCELISA) to determine infection, dissemination and transmission rates.
Findings: The infection and dissemination rates of the sylvatic DENV2 strain, QML22, were significantly lower than that for QML16. While the titres of virus in the bodies of mosquitoes infected with either of these viruses were similar, titres in legs and wings were significantly lower in mosquitoes infected with QML22 at most time points although they reached similar levels by 14 DPI. QML16 was detected in 16% (n = 25) and 28% (n = 25) of saliva expectorates at 10 and 14 DPI, respectively. In contrast, no virus was detected in the saliva expectorates of QML22 infected mosquitoes.
Conclusions: Australia urban/peri-urban A. aegypti species are susceptible to infection by the sylvatic and highly divergent DENV2 virus QML22. Our results indicate that replication of QML22 is attenuated relative to the contemporary strain QML16. Alternatively a salivary gland infection or escape barrier acts to prevent infection of saliva, potentially preventing onward transmission of this highly divergent virus in Australia.

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On 09 Apr, 2020
On 31 Mar, 2020
On 30 Mar, 2020
On 30 Mar, 2020
On 27 Mar, 2020
On 20 Mar, 2020
On 20 Mar, 2020
On 19 Mar, 2020
Posted 28 Feb, 2020
On 14 Mar, 2020
Received 11 Mar, 2020
On 02 Mar, 2020
Invitations sent on 02 Mar, 2020
On 02 Mar, 2020
Received 02 Mar, 2020
On 28 Feb, 2020
On 27 Feb, 2020
On 27 Feb, 2020
On 06 Feb, 2020
Received 26 Jan, 2020
Received 26 Jan, 2020
On 08 Jan, 2020
Received 23 Dec, 2019
On 15 Dec, 2019
On 09 Dec, 2019
Invitations sent on 06 Dec, 2019
On 03 Dec, 2019
On 02 Dec, 2019
On 02 Dec, 2019
On 02 Dec, 2019
Background: Humans are the primary hosts of dengue viruses (DENV). However, sylvatic cycles of transmission can occur among non-human primates and human encroachment into forested regions can be a source of emergence of new strains such as the highly divergent and sylvatic strain of DENV2, QML22, recovered from a dengue fever patient returning to Australia from Borneo. The objective of the present study was to evaluate the vector competence of Australian Aedes aegypti (A. aegypti) mosquitoes for this virus.
Methods: Four day old mosquitoes from two strains of A. aegypti from Queensland, Australia, were feed a meal of sheep blood containing 10 8 50% cell culture infectious dose per ml (CCID 50 /ml) of either QML22 or an epidemic strain of DENV serotype 2 (QML16) isolated from a dengue fever patient in Australia in 2015. Mosquitoes were maintained at 28°C, 75% relative humidity and sampled at 7, 10 and 14 days post-infection (DPI). Live virions in mosquito bodies (abdomen/thorax), legs and wings and saliva expectorates from individual mosquitoes were quantified using a Cell Culture Enzyme-linked Immunosorbant Assay (CCELISA) to determine infection, dissemination and transmission rates.
Findings: The infection and dissemination rates of the sylvatic DENV2 strain, QML22, were significantly lower than that for QML16. While the titres of virus in the bodies of mosquitoes infected with either of these viruses were similar, titres in legs and wings were significantly lower in mosquitoes infected with QML22 at most time points although they reached similar levels by 14 DPI. QML16 was detected in 16% (n = 25) and 28% (n = 25) of saliva expectorates at 10 and 14 DPI, respectively. In contrast, no virus was detected in the saliva expectorates of QML22 infected mosquitoes.
Conclusions: Australia urban/peri-urban A. aegypti species are susceptible to infection by the sylvatic and highly divergent DENV2 virus QML22. Our results indicate that replication of QML22 is attenuated relative to the contemporary strain QML16. Alternatively a salivary gland infection or escape barrier acts to prevent infection of saliva, potentially preventing onward transmission of this highly divergent virus in Australia.

Figure 1

Figure 2
This is a list of supplementary files associated with this preprint. Click to download.
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