Mosquito-borne Inkoo virus in northern Sweden - isolation and whole genome sequencing

Abstract

BackgroundInkoo virus (INKV) is a less known mosquito-borne virus belonging to Bunyaviridae, genus Orthobunyavirus, California serogroup. Studies indicate that INKV infection is mainly asymptomatic, but can cause mild encephalitis in humans. In northern Europe, the sero-prevalence against INKV is high, 41% in Sweden and 51% in Finland. Previously, INKV RNA has been detected in adult Aedes (Ae.) communis, Ae. hexodontus and Ae. punctor mosquitoes and Ae. communis larvae, but there are still gaps of knowledge regarding mosquito vectors and genetic diversity. Therefore, we aimed to determine the occurrence of INKV in its mosquito vector and characterize the isolates.MethodsAbout 125,000 mosquitoes were collected during a mosquito-borne virus surveillance in northern Sweden during the summer period of 2015. Of these, 10,000 mosquitoes were processed for virus isolation and detection using cell culture and RT-PCR. Virus isolates were further characterized by whole genome sequencing. Genetic typing of mosquito species was conducted by cytochrome oxidase subunit I (COI) gene amplification and sequencing (genetic barcoding).ResultsSeveral Ae. communis mosquitoes were found positive for INKV RNA and two isolates were obtained. The first complete sequences of the small (S), medium (M), and large (L) segments of INKV in Sweden were obtained. Phylogenetic analysis showed that the INKV genome was most closely related to other INKV isolates from Sweden and Finland. Of the three INKV genome segments, the INKV M segment had the highest frequency of non-synonymous mutations. The overall G/C-content of INKV genes was low for the N/NSs genes (43.8–45.5%), polyprotein (Gn/Gc/NSm) gene (35.6%) and the RNA polymerase gene (33.8%) This may be due to the fact that INKV in most instances utilized A or T in the third codon position.ConclusionsINKV is frequently circulating in northern Sweden and Ae. communis is the key vector. The high mutation rate of the INKV M segment may have consequences on virulenceElectronic supplementary materialThe online version of this article (doi:10.1186/s12985-017-0725-5) contains supplementary material, which is available to authorized users.

Inkoo and Sindbis viruses in blood sucking insects, and a serological study for Inkoo virus in semi-domesticated Eurasian tundra reindeer in Norway

“…punctor mosquitoes and in Ae. communis larvae [ 7 , 15 – 17 ]. The prevalence of INKV in the BSI population can possibly be affected by transovarial transmission of the virus, from infected mothers to the BSI progeny [ 1 ].…”

“…punctor mosquitoes, and in Ae. communis larvae, although there is a necessity for identification of mosquito vectors capable of transmitting INKV [ 7 , 15 – 17 ]. INKV has been found to be circulating in Northern Europe, including Norway [ 2 , 16 ].…”

Throw out the Map: Neuropathogenesis of the Globally Expanding California Serogroup of Orthobunyaviruses

“…ACHOV was isolated from mosquitoes in Panama [14], MELV in Trinidad and Brazil [13,51], and SDNV in Brazil [52]. INKV and CHATV are primarily found in Scandinavia and Russia [53,54,55,56], while TAHV is found throughout Europe, Russia, Asia, and Africa [53,57,58,59,60,61,62]. LUMV is the only CSG member found, thus far, exclusively in Africa [12,61].…”

Viromics Reveal a Number of Novel RNA Viruses in Swedish Mosquitoes

“…The majority of the metagenomic surveys of mosquitoes have been conducted in countries where arboviruses of human and animal health concern circulate, such as China, Australia, Mozambique, and the US [5,6,19,20]. In Sweden, two mosquito-borne viruses circulate: the arthralgia-associated Sindbis virus (SINV) [21] and Inkoo virus (INKV), which in rare cases, may cause mild encephalitis [22,23]. Further, it has been discussed whether WNV can be introduced to Sweden as it circulates in Southern and Central Europe, and the mosquito vector species, such as Culex (Cx.)…”