Abstract
BackgroundZika virus is an emerging pathogen of global importance. It has been responsible for recent outbreaks in the Americas and in the Pacific region. This study assessed five different mosquito species from the temperate climatic zone in Australia and included Aedes albopictus as a potentially invasive species.MethodsMosquitoes were orally challenged by membrane feeding with Zika virus strain of Cambodia 2010 origin, belonging to the Asian clade. Virus infection and dissemination were assessed by quantitative PCR on midgut and carcass after dissection. Transmission was assessed by determination of cytopathogenic effect of saliva (CPE) on Vero cells, followed by determination of 50% tissue culture infectious dose (TCID50) for CPE positive samples. Additionally, the presence of Wolbachia endosymbiont infection was assessed by qPCR and standard PCR.ResultsCulex mosquitoes were found unable to present Zika virus in saliva, as demonstrated by molecular as well as virological methods. Aedes aegypti, was used as a positive control for Zika infection and showed a high level of virus infection, dissemination and transmission. Local Aedes species, Ae. notoscriptus and, to a lesser degree, Ae. camptorhynchus were found to expel virus in their saliva and contained viral nucleic acid within the midgut. Molecular assessment identified low or no dissemination for these species, possibly due to low virus loads. Ae. albopictus from Torres Strait islands origin was shown as an efficient vector. Cx quinquefasciatus was shown to harbour Wolbachia endosymbionts at high prevalence, whilst no Wolbachia was found in Cx annulirostris. The Australian Ae. albopictus population was shown to harbour Wolbachia at high frequency.ConclusionsThe risk of local Aedes species triggering large Zika epidemics in the southern parts of Australia is low. The potentially invasive Ae. albopictus showed high prevalence of virus in the saliva and constitutes a potential threat if this mosquito species becomes established in mainland Australia. Complete risk analysis of Zika transmission in the temperate zone would require an assessment of the impact of temperature on Zika virus replication within local and invasive mosquito species.
Highlights
Zika virus is an emerging pathogen of global importance
The 6th, 7th and 11th generations were used for experimental viral challenge. - Aedes albopictus colony was established from egg batches collected in Hammond Island in the Torres Strait island group, at the top north of Australia, in Dec. 2015
The 50% tissue culture infectious dose (TCID50) of virus in the saliva of Ae. aegypti was found to be significantly higher than Ae. albopictus (p < 0.0001) and Ae. notoscriptus (p = 0.0002) (Fig. 2)
Summary
Zika virus is an emerging pathogen of global importance It has been responsible for recent outbreaks in the Americas and in the Pacific region. Primarily Aedes (Stegomyia) africanus, was suspected as the main sylvatic vector following direct isolation of Zika virus in 1956 [1]. Populations of Ae. aegypti [7] and Ae. albopictus [8] in Singapore have been shown efficacious vectors in the laboratory. (St.) hensilli, instead of Ae. aegypti was suspected of being responsible for the outbreak, and was shown experimentally capable of infection and dissemination [12]. In 2014, Zika virus reached the Americas and Ae. aegypti was shown to be a vector, both by molecular detection in field-collected mosquitoes [14] and experimental infection [14,15,16]. The role of other mosquito species is still under question, especially for Culex quinquefasciatus, with conflicting results which either showed it as an efficient experimental vector [14, 17] or not [16, 18, 19]
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