CRIMEAN CONGO HEMORRHAGIC FEVER

VIRUS CAUSING CRIMEAN CONGO HEMORRHAGIC FEVER

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NAIROVIRUS

NAIROVIRUS

        Nairovirus is a genus in the family Bunyaviridae that include viruses with circular, negative-sense single stranded RNA. It got its name from the Nairobi sheep disease that affects the gastrointestinal tracts of sheep and goats. Viruses in this genus are tick-borne viruses that can have human or animal hosts. There are seven species in this genus which include: Crimean-Congo hemorrhagic fever virus (CCHFV); Dugbe virus (DUGV); Qalyub virus (QYBV); Sakhalin virus (SAKV); Dera Ghazi Khan virus (DGKV); Thiafora virus (TFAV); and Hughes virus (HUGV)

Genome

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        Nairovirus genomes are monomeric, segmented, circular, negative sense, single-stranded RNA. The complete genome is about 17,100-22,800 nucleotides long and is segmented into three segments: large, medium, and small. The large segment is about 11000-14400 nucleotides long (6.8–12 kb) and it encodes for the nucleocapsid protein. The medium segment is about 4,400-6,300 nucleotides long (3.2-4.9kb) and it encodes for glycoproteins G¬n and Gc. The small segment is about 1,700-2,100 nucleotides long (1-3kb) and it encodes the viral polymerase.

        The genome has terminally redundant sequences with the sequences being repeated at both ends. The terminal nucleotides are base-paired forming non-covalently closed, circular RNA. Both the 5’ and 3’ end have conserved regions of 9 nucleotides in length. The sequences are 5’end UCUCAAAGA and 3’end AGAGUUUCU


Virion

        The virions for viruses in this genus have a spherical shape. They range in size from about 80-120 nm in diameter with 50% of their weight attributed to proteins and 20-30% of their weight attributed to lipids. The virions have 3 non-segmented, circular, symmetric nucleocapsids. The ribonucleocapsid is filamentous and has a length of about 200-300 nm and a width of about 2-2.5 nm.

        These nucleocapsids are surrounded by a single envelope that has projections made of glycoproteins protruding from its surface. These projections evenly cover the surface of the virion and are about 5-10 nm long. They aid in attachment to the host receptor in replication
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REPLICATION OF NAIROVIRUS

        These viruses are not dependent on a helper virus. They attach to the host receptors by their Gn-Gc glycoprotein dimer. The virus is then endocytosed into the host cell via a vesicle. The ribonucleocapsid segments are released into the cytoplasm commencing transcription. Transcription and replication occur in the cell and the newly synthesized virions are released by budding.
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