Genus Thogotovirus

Type Species	Thogoto virus	(THOV)

Distinguishing Features

Morphology and morphogenesis of these viruses show similarities with the influenzaviruses. Virions are reported to contain 6 (THOV) or 7 (DHOV) segments of linear, negative sense ssRNA. Total genomic size is about 10  kb. Sequences of the ends of vRNA are partially complementary and resemble those of influenzaviruses. The conserved end sequences of THOV viral RNAs are 5-AGAGA(U/A)AUCAAAGC . . . and 3-UCGUUUUUGUUC . . . ; for DHOV they are 5-AGUAGACAUCAA . . . and 3-UCGUU(A/U)UUGUUCG . . . The gene encoded by segment 1 is not known. The 2nd [DHOV] or 3rd [THOV] largest RNAs encode proteins (Mr 81 10³, 69 10³, respectively) that exhibit homology to influenzavirus P proteins. The single glycoprotein (GP, DHOV: Mr 65 10³; THOV: Mr 75 10³), is encoded by the 4th segment. It is unrelated to any influenzavirus protein but shows amino acid sequence similarity with the glycoprotein (gp64) of baculoviruses. The DHOV 5th segment encodes a protein (NP, Mr 54 10³) related to influenzavirus NP. The 6th segment (DHOV) encodes the 30 10³ M₁ protein, and may encode another M₂ (15 10³, protein not detected) of unknown function. The coding of the DHOV putative 7th segment is not known.

Antigenic Properties

Antigenic relationships between THOV and DHOV viruses are not apparent and none of the virus proteins are related antigenically to those of influenzaviruses; however, serological cross reactivity between DHOV and Batken virus has been demonstrated. For THOV and DHOV, several isolates have been made; however, the relationships of these isolates to the prototype viruses are not known.

Biological Properties

THOV and DHOV are transmitted between vertebrates by ticks. Comparatively low levels of hemagglutination occur at acidic pH and not at physiological pH. No receptor-destroying enzyme has been observed. Fusion of infected cells occurs at acidic pH and is inhibited by neutralizing monoclonal antibodies directed against GP, indicating that cell entry is via the endocytic pathway as for the influenzaviruses. Replication is inhibited by actinomycin-D. Nucleoprotein accumulates early in replication within the nucleus. GP is synthesized in the cytoplasm and accumulated at the cell surface. Reassortment between THOV temperature sensitive mutants has been demonstrated experimentally in dually infected ticks and in vertebrates.

List of Species Demarcation Criteria in the Genus

Thogotoviruses have been isolated from Boophilis sp. and Rhipicephalus sp. ticks in Kenya and Sicily as well as from Amblyomma variegatum ticks in Nigeria and Hyalomma sp. ticks in Nigeria and Egypt. Thogotoviruses have also been isolated in the central African Republic, Cameroon, Uganda, and Ethiopia as well as in southern Europe. Dhori viruses have a somewhat different, but overlapping geographic distribution that includes India, eastern Russia, as well as Egypt and southern Portugal. Dhori viruses have been isolated from Hyalomma sp. ticks. There is no detectable serological reactivity between THOV and DHOV and the structural differences (THOV has 6 RNA segments and DHOV have 7) and sequence diversity of 37% and 31% in the nucleoprotein and the envelope protein, respectively, argues for separate species status. Batken virus isolated from mosquitoes and ticks from Russia, cross reacts serologically with DHOV and shares 98% identity in a portion of the nucleoprotein and 90% identity an a portion of the envelope protein. These data suggest that Batken virus, although isolated from mosquitoes and ticks, is closely related to Dhori viruses.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:

Species in the Genus

Thogoto virus	[D00540, M77280]	(THOV)
Dhori virus	[M65866, M34002, M17435, M95567]	(DHOV)
Batken virus	[X97338, X97339]

Tentative Species in the Genus

None reported.

List of Unassigned Viruses in the Family

None reported.

Phylogenetic Relationships within the Family

See Fig. 3.

Similarity with Other Taxa

None reported.

Derivation of Names

Influenza: Italian form of Latin influentia, “epidemic”, originally used because epidemics were thought to be due to astrological or other occult “influences”.

Myxo: from Greek myxa, “mucus”.

Ortho: from Greek orthos, “straight”.