Quaranjavirus

Quaranjavirus is a genus of enveloped RNA viruses, one of seven genera in the virus family Orthomyxoviridae. The genome is single-stranded, negative-sense segmented RNA, generally with six segments. The genus contains six species. Quaranjaviruses predominantly infect arthropods and birds; Quaranfil quaranjavirus is the only member of the genus to have been shown to infect humans. The Quaranfil and Johnston Atoll viruses are transmitted between vertebrates by ticks, resembling members of Thogotovirus, another genus of Orthomyxoviridae.

Quaranfil virus was first isolated from humans in Egypt in 1953. Johnston Atoll virus and Lake Chad virus were first isolated from birds in 1964 and 1969, respectively. In 1989, based on the appearance of the virus particles under the electron microscope, H.G. Zeller and colleagues suggested that they should be classified as arenaviruses, but this was not accepted by the International Committee on Taxonomy of Viruses (ICTV). In 2009, based on sequence data and the structure of the virus particles, Rachel Presti and colleagues suggested that the three viruses should be classified as a new genus of orthomyxoviruses, originally named "Quarjavirus". Multiple other viruses have subsequently been suggested as genus members. The genus was formally proposed to the ICTV in 2012, under the name '"Quaranjavirus", and formally approved by that body in 2013.

Quaranfil virus is named for Quaranfil, one of the villages near Cairo from which the virus was isolated. The Johnston Atoll virus is named for Johnston Atoll in the Pacific, also where the virus was first isolated. The genus name combines "Quaran", with "ja" for Johnston Atoll.

The virus particle is enveloped and spherical, ovoid or variable in shape, with a diameter generally in the range 80–120 nm. The virus particle contains around ten ribosome-like granules, a feature of arenaviruses. It bears surface projections variously described as 4–5 nm long and 10–14 nm in length and 4–6 nm in diameter.

The single-stranded, –RNA genome is linear and segmented, generally with six segments of 0.9–2.4 kb and a total size of around 11.5 kb. Wellfleet Bay virus has a seventh segment of 519 nucleotides. The genome encodes six or (in Wellfleet Bay virus) seven proteins. The PA, PB1 and PB2 subunits of the trimeric RNA polymerase enzyme are encoded by the three largest segments (1–3), as in other orthomyxoviruses. Segment 5 encodes the envelope glycoprotein (GP). Proteins of unknown function are encoded by segments 4 and 6, which have recently been tentatively assigned to the viral nucleoprotein and matrix protein, respectively. Segment 7 of Wellfleet Bay virus encodes an additional protein of unknown function. The quaranjavirus glycoprotein shows no similarity with the influenza virus glycoproteins (haemagglutinin and neuraminidase), and instead shows some similarities with the gp64 glycoprotein of baculoviruses, which infect insects, as well as the glycoprotein of thogotoviruses, a genus of tick-transmitted orthomyxoviruses.

The replication cycle of Quaranfil virus takes around 24–36 hours, which is comparable with thogotoviruses and slower than influenza viruses.

Quaranjaviruses infect both arthropod and vertebrate hosts. The most common arthropod hosts are species of soft-bodied (Argasidae family) ticks. Most members cannot infect mosquito cell lines in the laboratory. In 2015, multiple new members of the genus were proposed based on RNA sequences obtained from mosquitos, flies, other insects, and the Neoscona spider.

Aquatic birds that nest in colonies are the most common vertebrate hosts, including gannets, terns and herons. Cygnet River and Wellfleet Bay viruses have been associated with an often-fatal disease in farmed and wild duck species, with symptoms including diarrhoea and lethargy. Most genus members tested can infect mice under laboratory conditions; they cause severe pathology and are frequently lethal. Quaranfil virus is the only member of the genus to have been shown to infect humans; infection generally appears to be asymptomatic and has occasionally been reported to be associated with mild fever.