Orthopoxvirus

Orthopoxvirus is a genus of large, enveloped, brick-shaped double-stranded DNA viruses in the family Poxviridae. Members replicate in the cytoplasm of infected cells and possess relatively large genomes, typically about 170 to 230 kilobases, encoding roughly 200 genes. The genus includes several well-known species that infect humans and animals, such as variola virus (the agent of smallpox), vaccinia virus (the vaccine strain), cowpox virus, monkeypox virus, camelpox virus, and ectromelia virus (mousepox).

Host range varies among species, with some viruses adapting to a broad spectrum of mammals and others more restricted. Transmission occurs through close contact with infectious lesions, bodily fluids, respiratory droplets, or contaminated objects, and some orthopoxviruses can cross species barriers in zoonotic transmissions.

Clinical features differ by virus but often involve febrile illness followed by a vesicular or pustular rash. Variola virus caused a highly virulent human disease prior to its eradication in 1980 through global vaccination efforts. Vaccination with vaccinia-based vaccines provides cross-protection against other orthopoxviruses, contributing to the historic control of smallpox and ongoing protection against related viruses.

Diagnosis is commonly achieved by nucleic acid testing (PCR), supported by virus isolation, electron microscopy, and serology in some settings. Treatment and prevention focus on vaccination strategies and infection-control measures. Antiviral agents with activity against orthopoxviruses, such as tecovirimat and cidofovir, are used in certain contexts and outbreaks.

Taxonomically, Orthopoxvirus lies within the subfamily Chordopoxvirinae of Poxviridae. The genus remains of public health interest due to zoonotic potential and occurrences of human-to-human transmission in outbreaks involving species like monkeypox.