Abstract
BackgroundCulex (Culex) tritaeniorhynchus is an important vector of Japanese encephalitis virus (JEV) affecting feral pigs, native mammals and humans. The mosquito species is widely distributed throughout Southeast Asia, Africa and Europe, and thought to be absent in Australia.MethodsIn February and May, 2020 the Medical Entomology unit of the Northern Territory (NT) Top End Health Service collected Cx. tritaeniorhynchus female specimens (n = 19) from the Darwin and Katherine regions. Specimens were preliminarily identified morphologically as the Vishnui subgroup in subgenus Culex. Molecular identification was performed using cytochrome c oxidase subunit 1 (COI) barcoding, including sequence percentage identity using BLAST and tree-based identification using maximum likelihood analysis in the IQ-TREE software package. Once identified using COI, specimens were reanalysed for diagnostic morphological characters to inform a new taxonomic key to related species from the NT.ResultsSequence percentage analysis of COI revealed that specimens from the NT shared 99.7% nucleotide identity to a haplotype of Cx. tritaeniorhynchus from Dili, Timor-Leste. The phylogenetic analysis showed that the NT specimens formed a monophyletic clade with other Cx. tritaeniorhynchus from Southeast Asia and the Middle East. We provide COI barcodes for most NT species from the Vishnui subgroup to aid future identifications, including the first genetic sequences for Culex (Culex) crinicauda and the undescribed species Culex (Culex) sp. No. 32 of Marks. Useful diagnostic morphological characters were identified and are presented in a taxonomic key to adult females to separate Cx. tritaeniorhynchus from other members of the Vishnui subgroup from the NT.ConclusionsWe report the detection of Cx. tritaeniorhynchus in Australia from the Darwin and Katherine regions of the NT. The vector is likely to be already established in northern Australia, given the wide geographical spread throughout the Top End of the NT. The establishment of Cx. tritaeniorhynchus in Australia is a concern to health officials as the species is an important vector of JEV and is now the sixth species from the subgenus Culex capable of vectoring JEV in Australia. We suggest that the species must now be continuously monitored during routine mosquito surveillance programmes to determine its current geographical spread and prevent the potential transmission of exotic JEV throughout Australia.Graphical abstract
Highlights
Culex (Culex) tritaeniorhynchus is an important vector of Japanese encephalitis virus (JEV) affecting feral pigs, native mammals and humans
Specimen collection Between February and May 2020, 33 adult female mosquitoes were collected from the Darwin and Katherine regions in the Northern Territory (NT), as part of the Medical Entomology (ME) Top End Health Service NT mosquito surveillance programme (Fig. 1; Additional file 1: Table S1); these were preliminarily identified as belonging to the Vishnui subgroup using the key to females of the subgenus Culex from the Australasian Region provided by Lee et al [2]
More than half (n = 19) of the Vishnui subgroup specimens sequenced from the NT were identified by c oxidase subunit 1 (COI) barcoding as Cx. tritaeniorhynchus, sharing 98.2– 98.8% nucleotide identity with records from Japan and/or Pakistan using Basic local alignment search tool (BLAST) in GenBank
Summary
Culex (Culex) tritaeniorhynchus is an important vector of Japanese encephalitis virus (JEV) affecting feral pigs, native mammals and humans. Culex (Culex) tritaeniorhynchus Giles, 1901 is a widespread mosquito species occurring throughout Southeast (SE) Asia and extending into the Middle East, Africa and Europe [1], but is considered absent from Australia [2, 3]. The vector is a concern to health officials as the species is an important vector of Japanese Encephalitis virus (JEV; Flaviviridae: Flavivirus). This arbovirus is the leading cause of viral encephalitis in humans, with 68,000 cases reported globally each year, resulting in 20,400 deaths (25% mortality rate) and 14,000–24,000 neurological impairments, many of which occur in children under the age of 12 years [4, 5]. The Australian species Culex (Culex) crinicauda Edwards, 1921, occurring in the NT, was once considered as belonging to the Vishnui subgroup by Marks [11] but was later excluded from the group by subsequent taxonomists [2]
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