Nairoviridae

Nairoviridae is a family of enveloped, negative-sense, segmented RNA viruses in the order Bunyavirales. It comprises the genus Orthonairovirus, which includes several species associated with ticks and vertebrate hosts. The virion is typically about 90–120 nm in diameter and contains three single-stranded RNA segments, designated L, M, and S. The L segment encodes the RNA-dependent RNA polymerase; the M segment encodes the viral glycoproteins Gn and Gc and a nonstructural protein; the S segment encodes the nucleocapsid protein and often a nonstructural product. The genome is negative-sense, and replication occurs in the cytoplasm. The segmented genome allows reassortment, contributing to genetic diversity.

Transmission is primarily via ticks, especially hard ticks of the genus Hyalomma for Crimean-Congo hemorrhagic fever virus. Vertebrate hosts include domestic and wild animals, which can serve as amplifying hosts. Humans may become infected through tick bites or contact with infected animal blood or tissues.

Notable members include Crimean-Congo hemorrhagic fever orthonairovirus, which causes Crimean-Congo hemorrhagic fever in humans, a severe hemorrhagic fever with substantial mortality in some outbreaks. Nairobi sheep disease orthonairovirus causes Nairobi sheep disease in small ruminants, characterized by hemorrhagic gastroenteritis and high mortality in affected flocks.

Diagnosis typically relies on molecular detection (RT-PCR), antigen detection, and serology. There are limited vaccines, primarily for veterinary use in some regions; human vaccines are not widely available. Prevention focuses on tick control, avoidance of tick bites, and biosafety when handling infected animals. Antiviral treatment is mainly supportive; ribavirin is used in some CCHF cases.