Abstract
Infections with emerging and re-emerging arboviruses are of increasing concern for global health. Tick-transmitted RNA viruses of the genus Thogotovirus in the Orthomyxoviridae family have considerable zoonotic potential, as indicated by the recent emergence of Bourbon virus in the USA. To successfully infect humans, arboviruses have to escape the restrictive power of the interferon defense system. This is exemplified by the high sensitivity of thogotoviruses to the antiviral action of the interferon-induced myxovirus resistance protein A (MxA) that inhibits the polymerase activity of incoming viral ribonucleoprotein complexes. Acquiring resistance to human MxA would be expected to enhance the zoonotic potential of these pathogens. Therefore, we screened a panel of 10 different thogotovirus isolates obtained from various parts of the world for their sensitivity to MxA. A single isolate from Nigeria, Jos virus, showed resistance to the antiviral action of MxA in cell culture and in MxA-transgenic mice, whereas the prototypic Sicilian isolate SiAr126 was fully MxA-sensitive. Further analysis identified two amino acid substitutions (G327R and R328V) in the viral nucleoprotein as determinants for MxA resistance. Importantly, when introduced into SiAr126, the R328V mutation resulted in complete MxA escape of the recombinant virus, without causing any viral fitness loss. The escape mutation abolished viral nucleoprotein recognition by MxA and allowed unhindered viral growth in MxA-expressing cells and in MxA-transgenic mice. These findings demonstrate that thogotoviruses can overcome the species barrier by escaping MxA restriction and reveal that these tick-transmitted viruses may have a greater zoonotic potential than previously suspected.
Highlights
The family of Orthomyxoviridae consists of seven genera: Influenzavirus A-D, Isavirus, Quaranfil virus and Thogotovirus [1,2]
Thogotovirus infections are known to cause isolated human fatalities, yet the zoonotic potential of these tick-transmitted pathogens is still largely unexplored. We examined if these viruses are able to escape the interferon-induced human myxovirus resistance protein A (MxA), thereby overcoming the human innate antiviral defense
The THOV-like viruses were potently inhibited by MxA with the striking exception of JOSV (Fig 1A)
Summary
The family of Orthomyxoviridae consists of seven genera: Influenzavirus A-D, Isavirus, Quaranfil virus and Thogotovirus [1,2]. Thogotoviruses are unique within this family because they are transmitted by ticks and circulate in diverse mammalian species including rodents, wild big game, sheep, cattle, and camels [4,5,6,7,8], causing a febrile illness and occasional abortions [9]. They phylogenetically cluster into Thogoto (THOV)-like and Dhori (DHOV)-like representatives of the genus Thogotovirus [1] and possess an envelope and a segmented single-stranded RNA genome of negative polarity [10]. The newly formed virions are released by budding from the cell membrane and can be transmitted by tick bites to new hosts [13,14]
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